[v5] Set the retain attribute on _elf_set_element if CC supports [BZ #27492]

  So that text_set_element/data_set_element/bss_set_element defined
variables will be retained by the linker.

Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
will not be optimized out; 'retain' prevents section garbage collection
if the linker support SHF_GNU_RETAIN.

GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
identifier name sections to be GCed even if there are live
__start_/__stop_ references.

Without the change, there are some static linking problems, e.g.
_IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
stdout is not flushed on exit.

Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
---
Changes in v1 -> v2:
* Define attribute_used_retain_section
Changes in v2 -> v3:
* Use attribute_used_retain instead attribute_used_retain_section
Changes in v3 -> v4:
* Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
Changes in v4 -> v5:
* Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
* Rename *gcc_retain* to *gnu_retain*
---
 config.h.in            |  3 +++
 configure              | 59 ++++++++++++++++++++++++++++++++++++++++++
 configure.ac           | 21 +++++++++++++++
 include/libc-symbols.h | 14 +++++++---
 libio/Makefile         | 32 +++++++++++++++++++++++
 libio/tst-cleanup.c    | 33 +++++++++++++++++++++++
 libio/tst-cleanup.exp  |  1 +
 7 files changed, 159 insertions(+), 4 deletions(-)
 create mode 100644 libio/tst-cleanup.c
 create mode 100644 libio/tst-cleanup.exp
  

On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song <maskray@google.com> wrote:
>
> So that text_set_element/data_set_element/bss_set_element defined
> variables will be retained by the linker.
>
> Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
> will not be optimized out; 'retain' prevents section garbage collection
> if the linker support SHF_GNU_RETAIN.
>
> GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
> identifier name sections to be GCed even if there are live
> __start_/__stop_ references.
>
> Without the change, there are some static linking problems, e.g.
> _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
> stdout is not flushed on exit.
>
> Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
> ---
> Changes in v1 -> v2:
> * Define attribute_used_retain_section
> Changes in v2 -> v3:
> * Use attribute_used_retain instead attribute_used_retain_section
> Changes in v3 -> v4:
> * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
> Changes in v4 -> v5:
> * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
> * Rename *gcc_retain* to *gnu_retain*
> ---
>  config.h.in            |  3 +++
>  configure              | 59 ++++++++++++++++++++++++++++++++++++++++++
>  configure.ac           | 21 +++++++++++++++
>  include/libc-symbols.h | 14 +++++++---
>  libio/Makefile         | 32 +++++++++++++++++++++++
>  libio/tst-cleanup.c    | 33 +++++++++++++++++++++++
>  libio/tst-cleanup.exp  |  1 +
>  7 files changed, 159 insertions(+), 4 deletions(-)
>  create mode 100644 libio/tst-cleanup.c
>  create mode 100644 libio/tst-cleanup.exp
>
> diff --git a/config.h.in b/config.h.in
> index ca1547ae67..96a08c7757 100644
> --- a/config.h.in
> +++ b/config.h.in
> @@ -187,6 +187,9 @@
>  /* Define if gcc supports attribute ifunc.  */
>  #undef HAVE_GCC_IFUNC
>
> +/* Define if CC supports attribute retain.  */
> +#undef HAVE_GNU_RETAIN
> +
>  /* Define if the linker defines __ehdr_start.  */
>  #undef HAVE_EHDR_START
>
> diff --git a/configure b/configure
> index fcf43bf7de..e64b7f8efe 100755
> --- a/configure
> +++ b/configure
> @@ -4105,6 +4105,31 @@ fi
>  $as_echo "$libc_cv_textrel_ifunc" >&6; }
>
>
> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
> +if ${libc_cv_gnu_retain+:} false; then :
> +  $as_echo_n "(cached) " >&6
> +else
> +  cat > conftest.c <<EOF
> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> +EOF
> +libc_cv_gnu_retain=no
> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> +   2>&5 ; then
> +  libc_cv_gnu_retain=yes
> +fi
> +rm -f conftest*
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
> +$as_echo "$libc_cv_gnu_retain" >&6; }
> +if test $libc_cv_gnu_retain = yes; then
> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
> +
> +fi
> +config_vars="$config_vars
> +have-gnu-retain = $libc_cv_gnu_retain"
> +
>  # Check if gcc warns about alias for function with incompatible types.
>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
>  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
> @@ -5871,6 +5896,40 @@ fi
>  $as_echo "$libc_linker_feature" >&6; }
>
>
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
> +libc_linker_feature=no
> +if test x"$gnu_ld" = x"yes"; then
> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
> +  if test -n "$libc_linker_check"; then
> +    cat > conftest.c <<EOF
> +int _start (void) { return 42; }
> +EOF
> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
> +                               -fPIC -shared -o conftest.so conftest.c
> +                               1>&5'
> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> +  (eval $ac_try) 2>&5
> +  ac_status=$?
> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> +  test $ac_status = 0; }; }
> +    then
> +      libc_linker_feature=yes
> +    fi
> +    rm -f conftest*
> +  fi
> +fi
> +if test $libc_linker_feature = yes; then
> +  libc_cv_z_start_stop_gc=yes
> +else
> +  libc_cv_z_start_stop_gc=no
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> +$as_echo "$libc_linker_feature" >&6; }
> +config_vars="$config_vars
> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
> +
>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>  libc_linker_feature=no
> diff --git a/configure.ac b/configure.ac
> index fce967f2c2..cc47e56e82 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -707,6 +707,23 @@ fi
>  rm -f conftest*])
>  AC_SUBST(libc_cv_textrel_ifunc)
>
> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> +AC_CACHE_CHECK([for GNU attribute retain support],
> +              libc_cv_gnu_retain, [dnl
> +cat > conftest.c <<EOF
> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> +EOF
> +libc_cv_gnu_retain=no
> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
> +   2>&AS_MESSAGE_LOG_FD ; then
> +  libc_cv_gnu_retain=yes
> +fi
> +rm -f conftest*])
> +if test $libc_cv_gnu_retain = yes; then
> +  AC_DEFINE(HAVE_GNU_RETAIN)
> +fi
> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
> +
>  # Check if gcc warns about alias for function with incompatible types.
>  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>                libc_cv_gcc_incompatible_alias, [dnl
> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>  AC_SUBST(libc_cv_z_execstack)
>
> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
> +
>  LIBC_LINKER_FEATURE([--no-dynamic-linker],
>                     [-Wl,--no-dynamic-linker],
>                     [libc_cv_no_dynamic_linker=yes],
> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
> index 546fc26a7b..127ea656c2 100644
> --- a/include/libc-symbols.h
> +++ b/include/libc-symbols.h
> @@ -352,6 +352,12 @@ for linking")
>
>  */
>
> +#ifdef HAVE_GNU_RETAIN
> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
> +#else
> +# define attribute_used_retain __attribute__ ((__used__))
> +#endif
> +
>  /* Symbol set support macros.  */
>
>  /* Make SYMBOL, which is in the text segment, an element of SET.  */
> @@ -367,12 +373,12 @@ for linking")
>  /* When building a shared library, make the set section writable,
>     because it will need to be relocated at run time anyway.  */
>  # define _elf_set_element(set, symbol) \
> -  static const void *__elf_set_##set##_element_##symbol##__ \
> -    __attribute__ ((used, section (#set))) = &(symbol)
> +    static const void *__elf_set_##set##_element_##symbol##__ \
> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>  #else
>  # define _elf_set_element(set, symbol) \
> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> -    __attribute__ ((used, section (#set))) = &(symbol)
> +    static const void *const __elf_set_##set##_element_##symbol##__ \
> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>  #endif
>
>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
> diff --git a/libio/Makefile b/libio/Makefile
> index 12ce41038f..c9c232ebc2 100644
> --- a/libio/Makefile
> +++ b/libio/Makefile
> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared))
>  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>                  $(objpfx)tst-bz24228-mem.out
>  endif
> +
> +tests += tst-cleanup-default
> +tests-static += tst-cleanup-default
> +tests-special += $(objpfx)tst-cleanup-default-cmp.out

Please make 2 tests,  tst-cleanup-default and tst-cleanup-default-static.

> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> +
> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> +tests += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> +tests-static += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out

Same here.

> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
> +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc
> +endif
>  endif
>
>  include ../Rules
> @@ -224,6 +238,24 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>  $(objpfx)tst-wfile-sync.out: $(gen-locales)
>  endif
>
> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> +       cmp $^ > $@; \
> +       $(evaluate-test)
> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
> +       $(compile.c) -o $@
> +
> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> +       cmp $^ > $@; \
> +       $(evaluate-test)
> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> +       $(compile.c) -o $@
> +
> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
> +       cmp $^ > $@; \
> +       $(evaluate-test)
> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
> +       $(compile.c) -o $@
>
>  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>         $(common-objpfx)libio/; \
> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
> new file mode 100644
> index 0000000000..7f0a34a91e
> --- /dev/null
> +++ b/libio/tst-cleanup.c
> @@ -0,0 +1,33 @@

Please add a comment saying that test --gc-sections.

> +/* Copyright (C) 2021 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +/* Test that stdout is flushed after atexit callbacks were run.  */
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +
> +void
> +hook (void)
> +{
> +  puts ("hello");
> +}
> +
> +int
> +main (void)
> +{
> +  atexit (hook);
> +}
> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
> new file mode 100644
> index 0000000000..ce01362503
> --- /dev/null
> +++ b/libio/tst-cleanup.exp
> @@ -0,0 +1 @@
> +hello
> --
> 2.31.0.291.g576ba9dcdaf-goog
>
  

On 2021-04-01, H.J. Lu wrote:
>On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song <maskray@google.com> wrote:
>>
>> So that text_set_element/data_set_element/bss_set_element defined
>> variables will be retained by the linker.
>>
>> Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
>> will not be optimized out; 'retain' prevents section garbage collection
>> if the linker support SHF_GNU_RETAIN.
>>
>> GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
>> identifier name sections to be GCed even if there are live
>> __start_/__stop_ references.
>>
>> Without the change, there are some static linking problems, e.g.
>> _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
>> stdout is not flushed on exit.
>>
>> Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
>> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
>> ---
>> Changes in v1 -> v2:
>> * Define attribute_used_retain_section
>> Changes in v2 -> v3:
>> * Use attribute_used_retain instead attribute_used_retain_section
>> Changes in v3 -> v4:
>> * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
>> Changes in v4 -> v5:
>> * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
>> * Rename *gcc_retain* to *gnu_retain*
>> ---
>>  config.h.in            |  3 +++
>>  configure              | 59 ++++++++++++++++++++++++++++++++++++++++++
>>  configure.ac           | 21 +++++++++++++++
>>  include/libc-symbols.h | 14 +++++++---
>>  libio/Makefile         | 32 +++++++++++++++++++++++
>>  libio/tst-cleanup.c    | 33 +++++++++++++++++++++++
>>  libio/tst-cleanup.exp  |  1 +
>>  7 files changed, 159 insertions(+), 4 deletions(-)
>>  create mode 100644 libio/tst-cleanup.c
>>  create mode 100644 libio/tst-cleanup.exp
>>
>> diff --git a/config.h.in b/config.h.in
>> index ca1547ae67..96a08c7757 100644
>> --- a/config.h.in
>> +++ b/config.h.in
>> @@ -187,6 +187,9 @@
>>  /* Define if gcc supports attribute ifunc.  */
>>  #undef HAVE_GCC_IFUNC
>>
>> +/* Define if CC supports attribute retain.  */
>> +#undef HAVE_GNU_RETAIN
>> +
>>  /* Define if the linker defines __ehdr_start.  */
>>  #undef HAVE_EHDR_START
>>
>> diff --git a/configure b/configure
>> index fcf43bf7de..e64b7f8efe 100755
>> --- a/configure
>> +++ b/configure
>> @@ -4105,6 +4105,31 @@ fi
>>  $as_echo "$libc_cv_textrel_ifunc" >&6; }
>>
>>
>> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
>> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
>> +if ${libc_cv_gnu_retain+:} false; then :
>> +  $as_echo_n "(cached) " >&6
>> +else
>> +  cat > conftest.c <<EOF
>> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> +EOF
>> +libc_cv_gnu_retain=no
>> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
>> +   2>&5 ; then
>> +  libc_cv_gnu_retain=yes
>> +fi
>> +rm -f conftest*
>> +fi
>> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
>> +$as_echo "$libc_cv_gnu_retain" >&6; }
>> +if test $libc_cv_gnu_retain = yes; then
>> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
>> +
>> +fi
>> +config_vars="$config_vars
>> +have-gnu-retain = $libc_cv_gnu_retain"
>> +
>>  # Check if gcc warns about alias for function with incompatible types.
>>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
>>  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
>> @@ -5871,6 +5896,40 @@ fi
>>  $as_echo "$libc_linker_feature" >&6; }
>>
>>
>> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
>> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
>> +libc_linker_feature=no
>> +if test x"$gnu_ld" = x"yes"; then
>> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
>> +  if test -n "$libc_linker_check"; then
>> +    cat > conftest.c <<EOF
>> +int _start (void) { return 42; }
>> +EOF
>> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
>> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
>> +                               -fPIC -shared -o conftest.so conftest.c
>> +                               1>&5'
>> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
>> +  (eval $ac_try) 2>&5
>> +  ac_status=$?
>> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
>> +  test $ac_status = 0; }; }
>> +    then
>> +      libc_linker_feature=yes
>> +    fi
>> +    rm -f conftest*
>> +  fi
>> +fi
>> +if test $libc_linker_feature = yes; then
>> +  libc_cv_z_start_stop_gc=yes
>> +else
>> +  libc_cv_z_start_stop_gc=no
>> +fi
>> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
>> +$as_echo "$libc_linker_feature" >&6; }
>> +config_vars="$config_vars
>> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
>> +
>>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>>  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>>  libc_linker_feature=no
>> diff --git a/configure.ac b/configure.ac
>> index fce967f2c2..cc47e56e82 100644
>> --- a/configure.ac
>> +++ b/configure.ac
>> @@ -707,6 +707,23 @@ fi
>>  rm -f conftest*])
>>  AC_SUBST(libc_cv_textrel_ifunc)
>>
>> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> +AC_CACHE_CHECK([for GNU attribute retain support],
>> +              libc_cv_gnu_retain, [dnl
>> +cat > conftest.c <<EOF
>> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> +EOF
>> +libc_cv_gnu_retain=no
>> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
>> +   2>&AS_MESSAGE_LOG_FD ; then
>> +  libc_cv_gnu_retain=yes
>> +fi
>> +rm -f conftest*])
>> +if test $libc_cv_gnu_retain = yes; then
>> +  AC_DEFINE(HAVE_GNU_RETAIN)
>> +fi
>> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
>> +
>>  # Check if gcc warns about alias for function with incompatible types.
>>  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>>                libc_cv_gcc_incompatible_alias, [dnl
>> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>>  AC_SUBST(libc_cv_z_execstack)
>>
>> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
>> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
>> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
>> +
>>  LIBC_LINKER_FEATURE([--no-dynamic-linker],
>>                     [-Wl,--no-dynamic-linker],
>>                     [libc_cv_no_dynamic_linker=yes],
>> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
>> index 546fc26a7b..127ea656c2 100644
>> --- a/include/libc-symbols.h
>> +++ b/include/libc-symbols.h
>> @@ -352,6 +352,12 @@ for linking")
>>
>>  */
>>
>> +#ifdef HAVE_GNU_RETAIN
>> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
>> +#else
>> +# define attribute_used_retain __attribute__ ((__used__))
>> +#endif
>> +
>>  /* Symbol set support macros.  */
>>
>>  /* Make SYMBOL, which is in the text segment, an element of SET.  */
>> @@ -367,12 +373,12 @@ for linking")
>>  /* When building a shared library, make the set section writable,
>>     because it will need to be relocated at run time anyway.  */
>>  # define _elf_set_element(set, symbol) \
>> -  static const void *__elf_set_##set##_element_##symbol##__ \
>> -    __attribute__ ((used, section (#set))) = &(symbol)
>> +    static const void *__elf_set_##set##_element_##symbol##__ \
>> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>>  #else
>>  # define _elf_set_element(set, symbol) \
>> -  static const void *const __elf_set_##set##_element_##symbol##__ \
>> -    __attribute__ ((used, section (#set))) = &(symbol)
>> +    static const void *const __elf_set_##set##_element_##symbol##__ \
>> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>>  #endif
>>
>>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
>> diff --git a/libio/Makefile b/libio/Makefile
>> index 12ce41038f..c9c232ebc2 100644
>> --- a/libio/Makefile
>> +++ b/libio/Makefile
>> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared))
>>  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>>                  $(objpfx)tst-bz24228-mem.out
>>  endif
>> +
>> +tests += tst-cleanup-default
>> +tests-static += tst-cleanup-default
>> +tests-special += $(objpfx)tst-cleanup-default-cmp.out
>
>Please make 2 tests,  tst-cleanup-default and tst-cleanup-default-static.

Added.

>> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> +
>> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> +tests += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
>> +tests-static += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
>> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
>
>Same here.

Added.

>> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
>> +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc
>> +endif
>>  endif
>>
>>  include ../Rules
>> @@ -224,6 +238,24 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>>  $(objpfx)tst-wfile-sync.out: $(gen-locales)
>>  endif
>>
>> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>> +
>> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>> +
>> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>>
>>  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>>         $(common-objpfx)libio/; \
>> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
>> new file mode 100644
>> index 0000000000..7f0a34a91e
>> --- /dev/null
>> +++ b/libio/tst-cleanup.c
>> @@ -0,0 +1,33 @@
>
>Please add a comment saying that test --gc-sections.

OK, added.

>> +/* Copyright (C) 2021 Free Software Foundation, Inc.
>> +   This file is part of the GNU C Library.
>> +
>> +   The GNU C Library is free software; you can redistribute it and/or
>> +   modify it under the terms of the GNU Lesser General Public
>> +   License as published by the Free Software Foundation; either
>> +   version 2.1 of the License, or (at your option) any later version.
>> +
>> +   The GNU C Library is distributed in the hope that it will be useful,
>> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> +   Lesser General Public License for more details.
>> +
>> +   You should have received a copy of the GNU Lesser General Public
>> +   License along with the GNU C Library; if not, see
>> +   <https://www.gnu.org/licenses/>.  */
>> +
>> +/* Test that stdout is flushed after atexit callbacks were run.  */
>> +
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +
>> +void
>> +hook (void)
>> +{
>> +  puts ("hello");
>> +}
>> +
>> +int
>> +main (void)
>> +{
>> +  atexit (hook);
>> +}
>> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
>> new file mode 100644
>> index 0000000000..ce01362503
>> --- /dev/null
>> +++ b/libio/tst-cleanup.exp
>> @@ -0,0 +1 @@
>> +hello
>> --
>> 2.31.0.291.g576ba9dcdaf-goog
>>
>

diff --git a/config.h.in b/config.h.in
index ca1547ae67..96a08c7757 100644
--- a/config.h.in
+++ b/config.h.in
@@ -187,6 +187,9 @@
  /* Define if gcc supports attribute ifunc.  */
  #undef HAVE_GCC_IFUNC
  
+/* Define if CC supports attribute retain.  */
+#undef HAVE_GNU_RETAIN
+
  /* Define if the linker defines __ehdr_start.  */
  #undef HAVE_EHDR_START
  
diff --git a/configure b/configure
index fcf43bf7de..e64b7f8efe 100755
--- a/configure
+++ b/configure
@@ -4105,6 +4105,31 @@ fi
  $as_echo "$libc_cv_textrel_ifunc" >&6; }
  
  
+# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
+$as_echo_n "checking for GNU attribute retain support... " >&6; }
+if ${libc_cv_gnu_retain+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat > conftest.c <<EOF
+static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
+EOF
+libc_cv_gnu_retain=no
+if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
+   2>&5 ; then
+  libc_cv_gnu_retain=yes
+fi
+rm -f conftest*
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
+$as_echo "$libc_cv_gnu_retain" >&6; }
+if test $libc_cv_gnu_retain = yes; then
+  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
+
+fi
+config_vars="$config_vars
+have-gnu-retain = $libc_cv_gnu_retain"
+
  # Check if gcc warns about alias for function with incompatible types.
  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
@@ -5871,6 +5896,40 @@ fi
  $as_echo "$libc_linker_feature" >&6; }
  
  
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
+$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
+  if test -n "$libc_linker_check"; then
+    cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+				-Wl,-z,start-stop-gc -nostdlib -nostartfiles
+				-fPIC -shared -o conftest.so conftest.c
+				1>&5'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; }
+    then
+      libc_linker_feature=yes
+    fi
+    rm -f conftest*
+  fi
+fi
+if test $libc_linker_feature = yes; then
+  libc_cv_z_start_stop_gc=yes
+else
+  libc_cv_z_start_stop_gc=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
+
  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
  libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index fce967f2c2..cc47e56e82 100644
--- a/configure.ac
+++ b/configure.ac
@@ -707,6 +707,23 @@ fi
  rm -f conftest*])
  AC_SUBST(libc_cv_textrel_ifunc)
  
+# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
+AC_CACHE_CHECK([for GNU attribute retain support],
+	       libc_cv_gnu_retain, [dnl
+cat > conftest.c <<EOF
+static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
+EOF
+libc_cv_gnu_retain=no
+if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
+   2>&AS_MESSAGE_LOG_FD ; then
+  libc_cv_gnu_retain=yes
+fi
+rm -f conftest*])
+if test $libc_cv_gnu_retain = yes; then
+  AC_DEFINE(HAVE_GNU_RETAIN)
+fi
+LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
+
  # Check if gcc warns about alias for function with incompatible types.
  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
  	       libc_cv_gcc_incompatible_alias, [dnl
@@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
  		    [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
  AC_SUBST(libc_cv_z_execstack)
  
+LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
+		    [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
+LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
+
  LIBC_LINKER_FEATURE([--no-dynamic-linker],
  		    [-Wl,--no-dynamic-linker],
  		    [libc_cv_no_dynamic_linker=yes],
diff --git a/include/libc-symbols.h b/include/libc-symbols.h
index 546fc26a7b..127ea656c2 100644
--- a/include/libc-symbols.h
+++ b/include/libc-symbols.h
@@ -352,6 +352,12 @@ for linking")
  
  */
  
+#ifdef HAVE_GNU_RETAIN
+# define attribute_used_retain __attribute__ ((__used__, __retain__))
+#else
+# define attribute_used_retain __attribute__ ((__used__))
+#endif
+
  /* Symbol set support macros.  */
  
  /* Make SYMBOL, which is in the text segment, an element of SET.  */
@@ -367,12 +373,12 @@ for linking")
  /* When building a shared library, make the set section writable,
     because it will need to be relocated at run time anyway.  */
  # define _elf_set_element(set, symbol) \
-  static const void *__elf_set_##set##_element_##symbol##__ \
-    __attribute__ ((used, section (#set))) = &(symbol)
+    static const void *__elf_set_##set##_element_##symbol##__ \
+      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
  #else
  # define _elf_set_element(set, symbol) \
-  static const void *const __elf_set_##set##_element_##symbol##__ \
-    __attribute__ ((used, section (#set))) = &(symbol)
+    static const void *const __elf_set_##set##_element_##symbol##__ \
+      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
  #endif
  
  /* Define SET as a symbol set.  This may be required (it is in a.out) to
diff --git a/libio/Makefile b/libio/Makefile
index 12ce41038f..ad0d53bb49 100644
--- a/libio/Makefile
+++ b/libio/Makefile
@@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
  		 $(objpfx)tst-bz24228-mem.out
  endif
+
+tests += tst-cleanup-default tst-cleanup-default-static
+tests-static += tst-cleanup-default-static
+tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
+LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
+LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
+
+ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
+tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
+		tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
+tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
+tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
+		$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
+		$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
+		$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
+LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
+LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
+LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
+LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
+endif
  endif
  
  include ../Rules
@@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
  $(objpfx)tst-wfile-sync.out: $(gen-locales)
  endif
  
+$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
+	cmp $^ > $@; \
+	$(evaluate-test)
+$(objpfx)tst-cleanup-default.o: tst-cleanup.c
+	$(compile.c) -o $@
+$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
+	cmp $^ > $@; \
+	$(evaluate-test)
+$(objpfx)tst-cleanup-default-static.o: tst-cleanup.c
+	$(compile.c) -o $@
+
+$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
+	cmp $^ > $@; \
+	$(evaluate-test)
+$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
+	$(compile.c) -o $@
+$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
+	cmp $^ > $@; \
+	$(evaluate-test)
+$(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c
+	$(compile.c) -o $@
+
+$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
+	cmp $^ > $@; \
+	$(evaluate-test)
+$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
+	$(compile.c) -o $@
+$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc-static.out
+	cmp $^ > $@; \
+	$(evaluate-test)
+$(objpfx)tst-cleanup-nostart-stop-gc-static.o: tst-cleanup.c
+	$(compile.c) -o $@
+
  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
  	$(SHELL) $< $(common-objpfx) '$(test-program-prefix)'	\
  	$(common-objpfx)libio/; \
diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
new file mode 100644
index 0000000000..837feac164
--- /dev/null
+++ b/libio/tst-cleanup.c
@@ -0,0 +1,34 @@
+/* Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* Test that stdout is flushed after atexit callbacks were run, even if the
+ * executable is linked with --gc-sections.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+void
+hook (void)
+{
+  puts ("hello");
+}
+
+int
+main (void)
+{
+  atexit (hook);
+}
diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
new file mode 100644
index 0000000000..ce01362503
--- /dev/null
+++ b/libio/tst-cleanup.exp
@@ -0,0 +1 @@
+hello
  

On Thu, Apr 1, 2021 at 8:23 PM Fangrui Song <maskray@google.com> wrote:
>
> On 2021-04-01, H.J. Lu wrote:
> >On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song <maskray@google.com> wrote:
> >>
> >> So that text_set_element/data_set_element/bss_set_element defined
> >> variables will be retained by the linker.
> >>
> >> Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
> >> will not be optimized out; 'retain' prevents section garbage collection
> >> if the linker support SHF_GNU_RETAIN.
> >>
> >> GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
> >> identifier name sections to be GCed even if there are live
> >> __start_/__stop_ references.
> >>
> >> Without the change, there are some static linking problems, e.g.
> >> _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
> >> stdout is not flushed on exit.
> >>
> >> Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
> >> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
> >> ---
> >> Changes in v1 -> v2:
> >> * Define attribute_used_retain_section
> >> Changes in v2 -> v3:
> >> * Use attribute_used_retain instead attribute_used_retain_section
> >> Changes in v3 -> v4:
> >> * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
> >> Changes in v4 -> v5:
> >> * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
> >> * Rename *gcc_retain* to *gnu_retain*
> >> ---
> >>  config.h.in            |  3 +++
> >>  configure              | 59 ++++++++++++++++++++++++++++++++++++++++++
> >>  configure.ac           | 21 +++++++++++++++
> >>  include/libc-symbols.h | 14 +++++++---
> >>  libio/Makefile         | 32 +++++++++++++++++++++++
> >>  libio/tst-cleanup.c    | 33 +++++++++++++++++++++++
> >>  libio/tst-cleanup.exp  |  1 +
> >>  7 files changed, 159 insertions(+), 4 deletions(-)
> >>  create mode 100644 libio/tst-cleanup.c
> >>  create mode 100644 libio/tst-cleanup.exp
> >>
> >> diff --git a/config.h.in b/config.h.in
> >> index ca1547ae67..96a08c7757 100644
> >> --- a/config.h.in
> >> +++ b/config.h.in
> >> @@ -187,6 +187,9 @@
> >>  /* Define if gcc supports attribute ifunc.  */
> >>  #undef HAVE_GCC_IFUNC
> >>
> >> +/* Define if CC supports attribute retain.  */
> >> +#undef HAVE_GNU_RETAIN
> >> +
> >>  /* Define if the linker defines __ehdr_start.  */
> >>  #undef HAVE_EHDR_START
> >>
> >> diff --git a/configure b/configure
> >> index fcf43bf7de..e64b7f8efe 100755
> >> --- a/configure
> >> +++ b/configure
> >> @@ -4105,6 +4105,31 @@ fi
> >>  $as_echo "$libc_cv_textrel_ifunc" >&6; }
> >>
> >>
> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
> >> +if ${libc_cv_gnu_retain+:} false; then :
> >> +  $as_echo_n "(cached) " >&6
> >> +else
> >> +  cat > conftest.c <<EOF
> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> +EOF
> >> +libc_cv_gnu_retain=no
> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> >> +   2>&5 ; then
> >> +  libc_cv_gnu_retain=yes
> >> +fi
> >> +rm -f conftest*
> >> +fi
> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
> >> +if test $libc_cv_gnu_retain = yes; then
> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
> >> +
> >> +fi
> >> +config_vars="$config_vars
> >> +have-gnu-retain = $libc_cv_gnu_retain"
> >> +
> >>  # Check if gcc warns about alias for function with incompatible types.
> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
> >>  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
> >> @@ -5871,6 +5896,40 @@ fi
> >>  $as_echo "$libc_linker_feature" >&6; }
> >>
> >>
> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
> >> +libc_linker_feature=no
> >> +if test x"$gnu_ld" = x"yes"; then
> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
> >> +  if test -n "$libc_linker_check"; then
> >> +    cat > conftest.c <<EOF
> >> +int _start (void) { return 42; }
> >> +EOF
> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
> >> +                               -fPIC -shared -o conftest.so conftest.c
> >> +                               1>&5'
> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> >> +  (eval $ac_try) 2>&5
> >> +  ac_status=$?
> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> >> +  test $ac_status = 0; }; }
> >> +    then
> >> +      libc_linker_feature=yes
> >> +    fi
> >> +    rm -f conftest*
> >> +  fi
> >> +fi
> >> +if test $libc_linker_feature = yes; then
> >> +  libc_cv_z_start_stop_gc=yes
> >> +else
> >> +  libc_cv_z_start_stop_gc=no
> >> +fi
> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> >> +$as_echo "$libc_linker_feature" >&6; }
> >> +config_vars="$config_vars
> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
> >> +
> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
> >>  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
> >>  libc_linker_feature=no
> >> diff --git a/configure.ac b/configure.ac
> >> index fce967f2c2..cc47e56e82 100644
> >> --- a/configure.ac
> >> +++ b/configure.ac
> >> @@ -707,6 +707,23 @@ fi
> >>  rm -f conftest*])
> >>  AC_SUBST(libc_cv_textrel_ifunc)
> >>
> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> +AC_CACHE_CHECK([for GNU attribute retain support],
> >> +              libc_cv_gnu_retain, [dnl
> >> +cat > conftest.c <<EOF
> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> +EOF
> >> +libc_cv_gnu_retain=no
> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
> >> +   2>&AS_MESSAGE_LOG_FD ; then
> >> +  libc_cv_gnu_retain=yes
> >> +fi
> >> +rm -f conftest*])
> >> +if test $libc_cv_gnu_retain = yes; then
> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
> >> +fi
> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
> >> +
> >>  # Check if gcc warns about alias for function with incompatible types.
> >>  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
> >>                libc_cv_gcc_incompatible_alias, [dnl
> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
> >>  AC_SUBST(libc_cv_z_execstack)
> >>
> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
> >> +
> >>  LIBC_LINKER_FEATURE([--no-dynamic-linker],
> >>                     [-Wl,--no-dynamic-linker],
> >>                     [libc_cv_no_dynamic_linker=yes],
> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
> >> index 546fc26a7b..127ea656c2 100644
> >> --- a/include/libc-symbols.h
> >> +++ b/include/libc-symbols.h
> >> @@ -352,6 +352,12 @@ for linking")
> >>
> >>  */
> >>
> >> +#ifdef HAVE_GNU_RETAIN
> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
> >> +#else
> >> +# define attribute_used_retain __attribute__ ((__used__))
> >> +#endif
> >> +
> >>  /* Symbol set support macros.  */
> >>
> >>  /* Make SYMBOL, which is in the text segment, an element of SET.  */
> >> @@ -367,12 +373,12 @@ for linking")
> >>  /* When building a shared library, make the set section writable,
> >>     because it will need to be relocated at run time anyway.  */
> >>  # define _elf_set_element(set, symbol) \
> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >>  #else
> >>  # define _elf_set_element(set, symbol) \
> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >>  #endif
> >>
> >>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
> >> diff --git a/libio/Makefile b/libio/Makefile
> >> index 12ce41038f..c9c232ebc2 100644
> >> --- a/libio/Makefile
> >> +++ b/libio/Makefile
> >> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared))
> >>  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
> >>                  $(objpfx)tst-bz24228-mem.out
> >>  endif
> >> +
> >> +tests += tst-cleanup-default
> >> +tests-static += tst-cleanup-default
> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out
> >
> >Please make 2 tests,  tst-cleanup-default and tst-cleanup-default-static.
>
> Added.
>
> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> >> +
> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> >> +tests-static += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
> >
> >Same here.
>
> Added.
>
> >> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
> >> +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc
> >> +endif
> >>  endif
> >>
> >>  include ../Rules
> >> @@ -224,6 +238,24 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >>  $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >>  endif
> >>
> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
> >> +       $(compile.c) -o $@
> >> +
> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> >> +       $(compile.c) -o $@
> >> +
> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
> >> +       $(compile.c) -o $@
> >>
> >>  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
> >>         $(common-objpfx)libio/; \
> >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
> >> new file mode 100644
> >> index 0000000000..7f0a34a91e
> >> --- /dev/null
> >> +++ b/libio/tst-cleanup.c
> >> @@ -0,0 +1,33 @@
> >
> >Please add a comment saying that test --gc-sections.
>
> OK, added.
>
> >> +/* Copyright (C) 2021 Free Software Foundation, Inc.
> >> +   This file is part of the GNU C Library.
> >> +
> >> +   The GNU C Library is free software; you can redistribute it and/or
> >> +   modify it under the terms of the GNU Lesser General Public
> >> +   License as published by the Free Software Foundation; either
> >> +   version 2.1 of the License, or (at your option) any later version.
> >> +
> >> +   The GNU C Library is distributed in the hope that it will be useful,
> >> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> >> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> >> +   Lesser General Public License for more details.
> >> +
> >> +   You should have received a copy of the GNU Lesser General Public
> >> +   License along with the GNU C Library; if not, see
> >> +   <https://www.gnu.org/licenses/>.  */
> >> +
> >> +/* Test that stdout is flushed after atexit callbacks were run.  */
> >> +
> >> +#include <stdio.h>
> >> +#include <stdlib.h>
> >> +
> >> +void
> >> +hook (void)
> >> +{
> >> +  puts ("hello");
> >> +}
> >> +
> >> +int
> >> +main (void)
> >> +{
> >> +  atexit (hook);
> >> +}
> >> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
> >> new file mode 100644
> >> index 0000000000..ce01362503
> >> --- /dev/null
> >> +++ b/libio/tst-cleanup.exp
> >> @@ -0,0 +1 @@
> >> +hello
> >> --
> >> 2.31.0.291.g576ba9dcdaf-goog
> >>
> >
>
> diff --git a/config.h.in b/config.h.in
> index ca1547ae67..96a08c7757 100644
> --- a/config.h.in
> +++ b/config.h.in
> @@ -187,6 +187,9 @@
>   /* Define if gcc supports attribute ifunc.  */
>   #undef HAVE_GCC_IFUNC
>
> +/* Define if CC supports attribute retain.  */
> +#undef HAVE_GNU_RETAIN
> +
>   /* Define if the linker defines __ehdr_start.  */
>   #undef HAVE_EHDR_START
>
> diff --git a/configure b/configure
> index fcf43bf7de..e64b7f8efe 100755
> --- a/configure
> +++ b/configure
> @@ -4105,6 +4105,31 @@ fi
>   $as_echo "$libc_cv_textrel_ifunc" >&6; }
>
>
> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
> +if ${libc_cv_gnu_retain+:} false; then :
> +  $as_echo_n "(cached) " >&6
> +else
> +  cat > conftest.c <<EOF
> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> +EOF
> +libc_cv_gnu_retain=no
> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> +   2>&5 ; then
> +  libc_cv_gnu_retain=yes
> +fi
> +rm -f conftest*
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
> +$as_echo "$libc_cv_gnu_retain" >&6; }
> +if test $libc_cv_gnu_retain = yes; then
> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
> +
> +fi
> +config_vars="$config_vars
> +have-gnu-retain = $libc_cv_gnu_retain"
> +
>   # Check if gcc warns about alias for function with incompatible types.
>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
>   $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
> @@ -5871,6 +5896,40 @@ fi
>   $as_echo "$libc_linker_feature" >&6; }
>
>
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
> +libc_linker_feature=no
> +if test x"$gnu_ld" = x"yes"; then
> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
> +  if test -n "$libc_linker_check"; then
> +    cat > conftest.c <<EOF
> +int _start (void) { return 42; }
> +EOF
> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
> +                               -fPIC -shared -o conftest.so conftest.c
> +                               1>&5'
> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> +  (eval $ac_try) 2>&5
> +  ac_status=$?
> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> +  test $ac_status = 0; }; }
> +    then
> +      libc_linker_feature=yes
> +    fi
> +    rm -f conftest*
> +  fi
> +fi
> +if test $libc_linker_feature = yes; then
> +  libc_cv_z_start_stop_gc=yes
> +else
> +  libc_cv_z_start_stop_gc=no
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> +$as_echo "$libc_linker_feature" >&6; }
> +config_vars="$config_vars
> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
> +
>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>   $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>   libc_linker_feature=no
> diff --git a/configure.ac b/configure.ac
> index fce967f2c2..cc47e56e82 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -707,6 +707,23 @@ fi
>   rm -f conftest*])
>   AC_SUBST(libc_cv_textrel_ifunc)
>
> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> +AC_CACHE_CHECK([for GNU attribute retain support],
> +              libc_cv_gnu_retain, [dnl
> +cat > conftest.c <<EOF
> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> +EOF
> +libc_cv_gnu_retain=no
> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
> +   2>&AS_MESSAGE_LOG_FD ; then
> +  libc_cv_gnu_retain=yes
> +fi
> +rm -f conftest*])
> +if test $libc_cv_gnu_retain = yes; then
> +  AC_DEFINE(HAVE_GNU_RETAIN)
> +fi
> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
> +
>   # Check if gcc warns about alias for function with incompatible types.
>   AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>                libc_cv_gcc_incompatible_alias, [dnl
> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>   AC_SUBST(libc_cv_z_execstack)
>
> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
> +
>   LIBC_LINKER_FEATURE([--no-dynamic-linker],
>                     [-Wl,--no-dynamic-linker],
>                     [libc_cv_no_dynamic_linker=yes],
> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
> index 546fc26a7b..127ea656c2 100644
> --- a/include/libc-symbols.h
> +++ b/include/libc-symbols.h
> @@ -352,6 +352,12 @@ for linking")
>
>   */
>
> +#ifdef HAVE_GNU_RETAIN
> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
> +#else
> +# define attribute_used_retain __attribute__ ((__used__))
> +#endif
> +
>   /* Symbol set support macros.  */
>
>   /* Make SYMBOL, which is in the text segment, an element of SET.  */
> @@ -367,12 +373,12 @@ for linking")
>   /* When building a shared library, make the set section writable,
>      because it will need to be relocated at run time anyway.  */
>   # define _elf_set_element(set, symbol) \
> -  static const void *__elf_set_##set##_element_##symbol##__ \
> -    __attribute__ ((used, section (#set))) = &(symbol)
> +    static const void *__elf_set_##set##_element_##symbol##__ \
> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>   #else
>   # define _elf_set_element(set, symbol) \
> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> -    __attribute__ ((used, section (#set))) = &(symbol)
> +    static const void *const __elf_set_##set##_element_##symbol##__ \
> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>   #endif
>
>   /* Define SET as a symbol set.  This may be required (it is in a.out) to
> diff --git a/libio/Makefile b/libio/Makefile
> index 12ce41038f..ad0d53bb49 100644
> --- a/libio/Makefile
> +++ b/libio/Makefile
> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>                  $(objpfx)tst-bz24228-mem.out
>   endif
> +
> +tests += tst-cleanup-default tst-cleanup-default-static
> +tests-static += tst-cleanup-default-static
> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
> +
> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
> +endif
>   endif
>
>   include ../Rules
> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>   endif
>
> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> +       cmp $^ > $@; \
> +       $(evaluate-test)
> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
> +       $(compile.c) -o $@
> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
> +       cmp $^ > $@; \
> +       $(evaluate-test)
> +$(objpfx)tst-cleanup-default-static.o: tst-cleanup.c
> +       $(compile.c) -o $@
> +
> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> +       cmp $^ > $@; \
> +       $(evaluate-test)
> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> +       $(compile.c) -o $@
> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
> +       cmp $^ > $@; \
> +       $(evaluate-test)
> +$(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c
> +       $(compile.c) -o $@

Please add a separate .c file for each test to get the correct dependency.

> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
> +       cmp $^ > $@; \
> +       $(evaluate-test)
> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
> +       $(compile.c) -o $@
> +$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc-static.out
> +       cmp $^ > $@; \
> +       $(evaluate-test)
> +$(objpfx)tst-cleanup-nostart-stop-gc-static.o: tst-cleanup.c
> +       $(compile.c) -o $@
> +
>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>         $(common-objpfx)libio/; \
> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
> new file mode 100644
> index 0000000000..837feac164
> --- /dev/null
> +++ b/libio/tst-cleanup.c
> @@ -0,0 +1,34 @@
> +/* Copyright (C) 2021 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +/* Test that stdout is flushed after atexit callbacks were run, even if the
> + * executable is linked with --gc-sections.  */
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +
> +void
> +hook (void)
> +{
> +  puts ("hello");
> +}
> +
> +int
> +main (void)
> +{
> +  atexit (hook);
> +}
> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
> new file mode 100644
> index 0000000000..ce01362503
> --- /dev/null
> +++ b/libio/tst-cleanup.exp
> @@ -0,0 +1 @@
> +hello
> --
> 2.31.0.208.g409f899ff0-goog
>
  

On 2021-04-02, H.J. Lu wrote:
>On Thu, Apr 1, 2021 at 8:23 PM Fangrui Song <maskray@google.com> wrote:
>>
>> On 2021-04-01, H.J. Lu wrote:
>> >On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song <maskray@google.com> wrote:
>> >>
>> >> So that text_set_element/data_set_element/bss_set_element defined
>> >> variables will be retained by the linker.
>> >>
>> >> Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
>> >> will not be optimized out; 'retain' prevents section garbage collection
>> >> if the linker support SHF_GNU_RETAIN.
>> >>
>> >> GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
>> >> identifier name sections to be GCed even if there are live
>> >> __start_/__stop_ references.
>> >>
>> >> Without the change, there are some static linking problems, e.g.
>> >> _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
>> >> stdout is not flushed on exit.
>> >>
>> >> Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
>> >> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
>> >> ---
>> >> Changes in v1 -> v2:
>> >> * Define attribute_used_retain_section
>> >> Changes in v2 -> v3:
>> >> * Use attribute_used_retain instead attribute_used_retain_section
>> >> Changes in v3 -> v4:
>> >> * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
>> >> Changes in v4 -> v5:
>> >> * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
>> >> * Rename *gcc_retain* to *gnu_retain*
>> >> ---
>> >>  config.h.in            |  3 +++
>> >>  configure              | 59 ++++++++++++++++++++++++++++++++++++++++++
>> >>  configure.ac           | 21 +++++++++++++++
>> >>  include/libc-symbols.h | 14 +++++++---
>> >>  libio/Makefile         | 32 +++++++++++++++++++++++
>> >>  libio/tst-cleanup.c    | 33 +++++++++++++++++++++++
>> >>  libio/tst-cleanup.exp  |  1 +
>> >>  7 files changed, 159 insertions(+), 4 deletions(-)
>> >>  create mode 100644 libio/tst-cleanup.c
>> >>  create mode 100644 libio/tst-cleanup.exp
>> >>
>> >> diff --git a/config.h.in b/config.h.in
>> >> index ca1547ae67..96a08c7757 100644
>> >> --- a/config.h.in
>> >> +++ b/config.h.in
>> >> @@ -187,6 +187,9 @@
>> >>  /* Define if gcc supports attribute ifunc.  */
>> >>  #undef HAVE_GCC_IFUNC
>> >>
>> >> +/* Define if CC supports attribute retain.  */
>> >> +#undef HAVE_GNU_RETAIN
>> >> +
>> >>  /* Define if the linker defines __ehdr_start.  */
>> >>  #undef HAVE_EHDR_START
>> >>
>> >> diff --git a/configure b/configure
>> >> index fcf43bf7de..e64b7f8efe 100755
>> >> --- a/configure
>> >> +++ b/configure
>> >> @@ -4105,6 +4105,31 @@ fi
>> >>  $as_echo "$libc_cv_textrel_ifunc" >&6; }
>> >>
>> >>
>> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
>> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
>> >> +if ${libc_cv_gnu_retain+:} false; then :
>> >> +  $as_echo_n "(cached) " >&6
>> >> +else
>> >> +  cat > conftest.c <<EOF
>> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> +EOF
>> >> +libc_cv_gnu_retain=no
>> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
>> >> +   2>&5 ; then
>> >> +  libc_cv_gnu_retain=yes
>> >> +fi
>> >> +rm -f conftest*
>> >> +fi
>> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
>> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
>> >> +if test $libc_cv_gnu_retain = yes; then
>> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
>> >> +
>> >> +fi
>> >> +config_vars="$config_vars
>> >> +have-gnu-retain = $libc_cv_gnu_retain"
>> >> +
>> >>  # Check if gcc warns about alias for function with incompatible types.
>> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
>> >>  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
>> >> @@ -5871,6 +5896,40 @@ fi
>> >>  $as_echo "$libc_linker_feature" >&6; }
>> >>
>> >>
>> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
>> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
>> >> +libc_linker_feature=no
>> >> +if test x"$gnu_ld" = x"yes"; then
>> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
>> >> +  if test -n "$libc_linker_check"; then
>> >> +    cat > conftest.c <<EOF
>> >> +int _start (void) { return 42; }
>> >> +EOF
>> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
>> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
>> >> +                               -fPIC -shared -o conftest.so conftest.c
>> >> +                               1>&5'
>> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
>> >> +  (eval $ac_try) 2>&5
>> >> +  ac_status=$?
>> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
>> >> +  test $ac_status = 0; }; }
>> >> +    then
>> >> +      libc_linker_feature=yes
>> >> +    fi
>> >> +    rm -f conftest*
>> >> +  fi
>> >> +fi
>> >> +if test $libc_linker_feature = yes; then
>> >> +  libc_cv_z_start_stop_gc=yes
>> >> +else
>> >> +  libc_cv_z_start_stop_gc=no
>> >> +fi
>> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
>> >> +$as_echo "$libc_linker_feature" >&6; }
>> >> +config_vars="$config_vars
>> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
>> >> +
>> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>> >>  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>> >>  libc_linker_feature=no
>> >> diff --git a/configure.ac b/configure.ac
>> >> index fce967f2c2..cc47e56e82 100644
>> >> --- a/configure.ac
>> >> +++ b/configure.ac
>> >> @@ -707,6 +707,23 @@ fi
>> >>  rm -f conftest*])
>> >>  AC_SUBST(libc_cv_textrel_ifunc)
>> >>
>> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> +AC_CACHE_CHECK([for GNU attribute retain support],
>> >> +              libc_cv_gnu_retain, [dnl
>> >> +cat > conftest.c <<EOF
>> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> +EOF
>> >> +libc_cv_gnu_retain=no
>> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
>> >> +   2>&AS_MESSAGE_LOG_FD ; then
>> >> +  libc_cv_gnu_retain=yes
>> >> +fi
>> >> +rm -f conftest*])
>> >> +if test $libc_cv_gnu_retain = yes; then
>> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
>> >> +fi
>> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
>> >> +
>> >>  # Check if gcc warns about alias for function with incompatible types.
>> >>  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>> >>                libc_cv_gcc_incompatible_alias, [dnl
>> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>> >>  AC_SUBST(libc_cv_z_execstack)
>> >>
>> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
>> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
>> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
>> >> +
>> >>  LIBC_LINKER_FEATURE([--no-dynamic-linker],
>> >>                     [-Wl,--no-dynamic-linker],
>> >>                     [libc_cv_no_dynamic_linker=yes],
>> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
>> >> index 546fc26a7b..127ea656c2 100644
>> >> --- a/include/libc-symbols.h
>> >> +++ b/include/libc-symbols.h
>> >> @@ -352,6 +352,12 @@ for linking")
>> >>
>> >>  */
>> >>
>> >> +#ifdef HAVE_GNU_RETAIN
>> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
>> >> +#else
>> >> +# define attribute_used_retain __attribute__ ((__used__))
>> >> +#endif
>> >> +
>> >>  /* Symbol set support macros.  */
>> >>
>> >>  /* Make SYMBOL, which is in the text segment, an element of SET.  */
>> >> @@ -367,12 +373,12 @@ for linking")
>> >>  /* When building a shared library, make the set section writable,
>> >>     because it will need to be relocated at run time anyway.  */
>> >>  # define _elf_set_element(set, symbol) \
>> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
>> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
>> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >>  #else
>> >>  # define _elf_set_element(set, symbol) \
>> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >>  #endif
>> >>
>> >>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
>> >> diff --git a/libio/Makefile b/libio/Makefile
>> >> index 12ce41038f..c9c232ebc2 100644
>> >> --- a/libio/Makefile
>> >> +++ b/libio/Makefile
>> >> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared))
>> >>  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>> >>                  $(objpfx)tst-bz24228-mem.out
>> >>  endif
>> >> +
>> >> +tests += tst-cleanup-default
>> >> +tests-static += tst-cleanup-default
>> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out
>> >
>> >Please make 2 tests,  tst-cleanup-default and tst-cleanup-default-static.
>>
>> Added.
>>
>> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> >> +
>> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
>> >> +tests-static += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
>> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
>> >
>> >Same here.
>>
>> Added.
>>
>> >> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
>> >> +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc
>> >> +endif
>> >>  endif
>> >>
>> >>  include ../Rules
>> >> @@ -224,6 +238,24 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>> >>  $(objpfx)tst-wfile-sync.out: $(gen-locales)
>> >>  endif
>> >>
>> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
>> >> +       $(compile.c) -o $@
>> >> +
>> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> >> +       $(compile.c) -o $@
>> >> +
>> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
>> >> +       $(compile.c) -o $@
>> >>
>> >>  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>> >>         $(common-objpfx)libio/; \
>> >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
>> >> new file mode 100644
>> >> index 0000000000..7f0a34a91e
>> >> --- /dev/null
>> >> +++ b/libio/tst-cleanup.c
>> >> @@ -0,0 +1,33 @@
>> >
>> >Please add a comment saying that test --gc-sections.
>>
>> OK, added.
>>
>> >> +/* Copyright (C) 2021 Free Software Foundation, Inc.
>> >> +   This file is part of the GNU C Library.
>> >> +
>> >> +   The GNU C Library is free software; you can redistribute it and/or
>> >> +   modify it under the terms of the GNU Lesser General Public
>> >> +   License as published by the Free Software Foundation; either
>> >> +   version 2.1 of the License, or (at your option) any later version.
>> >> +
>> >> +   The GNU C Library is distributed in the hope that it will be useful,
>> >> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>> >> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> >> +   Lesser General Public License for more details.
>> >> +
>> >> +   You should have received a copy of the GNU Lesser General Public
>> >> +   License along with the GNU C Library; if not, see
>> >> +   <https://www.gnu.org/licenses/>.  */
>> >> +
>> >> +/* Test that stdout is flushed after atexit callbacks were run.  */
>> >> +
>> >> +#include <stdio.h>
>> >> +#include <stdlib.h>
>> >> +
>> >> +void
>> >> +hook (void)
>> >> +{
>> >> +  puts ("hello");
>> >> +}
>> >> +
>> >> +int
>> >> +main (void)
>> >> +{
>> >> +  atexit (hook);
>> >> +}
>> >> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
>> >> new file mode 100644
>> >> index 0000000000..ce01362503
>> >> --- /dev/null
>> >> +++ b/libio/tst-cleanup.exp
>> >> @@ -0,0 +1 @@
>> >> +hello
>> >> --
>> >> 2.31.0.291.g576ba9dcdaf-goog
>> >>
>> >
>>
>> diff --git a/config.h.in b/config.h.in
>> index ca1547ae67..96a08c7757 100644
>> --- a/config.h.in
>> +++ b/config.h.in
>> @@ -187,6 +187,9 @@
>>   /* Define if gcc supports attribute ifunc.  */
>>   #undef HAVE_GCC_IFUNC
>>
>> +/* Define if CC supports attribute retain.  */
>> +#undef HAVE_GNU_RETAIN
>> +
>>   /* Define if the linker defines __ehdr_start.  */
>>   #undef HAVE_EHDR_START
>>
>> diff --git a/configure b/configure
>> index fcf43bf7de..e64b7f8efe 100755
>> --- a/configure
>> +++ b/configure
>> @@ -4105,6 +4105,31 @@ fi
>>   $as_echo "$libc_cv_textrel_ifunc" >&6; }
>>
>>
>> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
>> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
>> +if ${libc_cv_gnu_retain+:} false; then :
>> +  $as_echo_n "(cached) " >&6
>> +else
>> +  cat > conftest.c <<EOF
>> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> +EOF
>> +libc_cv_gnu_retain=no
>> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
>> +   2>&5 ; then
>> +  libc_cv_gnu_retain=yes
>> +fi
>> +rm -f conftest*
>> +fi
>> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
>> +$as_echo "$libc_cv_gnu_retain" >&6; }
>> +if test $libc_cv_gnu_retain = yes; then
>> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
>> +
>> +fi
>> +config_vars="$config_vars
>> +have-gnu-retain = $libc_cv_gnu_retain"
>> +
>>   # Check if gcc warns about alias for function with incompatible types.
>>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
>>   $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
>> @@ -5871,6 +5896,40 @@ fi
>>   $as_echo "$libc_linker_feature" >&6; }
>>
>>
>> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
>> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
>> +libc_linker_feature=no
>> +if test x"$gnu_ld" = x"yes"; then
>> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
>> +  if test -n "$libc_linker_check"; then
>> +    cat > conftest.c <<EOF
>> +int _start (void) { return 42; }
>> +EOF
>> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
>> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
>> +                               -fPIC -shared -o conftest.so conftest.c
>> +                               1>&5'
>> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
>> +  (eval $ac_try) 2>&5
>> +  ac_status=$?
>> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
>> +  test $ac_status = 0; }; }
>> +    then
>> +      libc_linker_feature=yes
>> +    fi
>> +    rm -f conftest*
>> +  fi
>> +fi
>> +if test $libc_linker_feature = yes; then
>> +  libc_cv_z_start_stop_gc=yes
>> +else
>> +  libc_cv_z_start_stop_gc=no
>> +fi
>> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
>> +$as_echo "$libc_linker_feature" >&6; }
>> +config_vars="$config_vars
>> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
>> +
>>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>>   $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>>   libc_linker_feature=no
>> diff --git a/configure.ac b/configure.ac
>> index fce967f2c2..cc47e56e82 100644
>> --- a/configure.ac
>> +++ b/configure.ac
>> @@ -707,6 +707,23 @@ fi
>>   rm -f conftest*])
>>   AC_SUBST(libc_cv_textrel_ifunc)
>>
>> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> +AC_CACHE_CHECK([for GNU attribute retain support],
>> +              libc_cv_gnu_retain, [dnl
>> +cat > conftest.c <<EOF
>> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> +EOF
>> +libc_cv_gnu_retain=no
>> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
>> +   2>&AS_MESSAGE_LOG_FD ; then
>> +  libc_cv_gnu_retain=yes
>> +fi
>> +rm -f conftest*])
>> +if test $libc_cv_gnu_retain = yes; then
>> +  AC_DEFINE(HAVE_GNU_RETAIN)
>> +fi
>> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
>> +
>>   # Check if gcc warns about alias for function with incompatible types.
>>   AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>>                libc_cv_gcc_incompatible_alias, [dnl
>> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>>   AC_SUBST(libc_cv_z_execstack)
>>
>> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
>> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
>> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
>> +
>>   LIBC_LINKER_FEATURE([--no-dynamic-linker],
>>                     [-Wl,--no-dynamic-linker],
>>                     [libc_cv_no_dynamic_linker=yes],
>> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
>> index 546fc26a7b..127ea656c2 100644
>> --- a/include/libc-symbols.h
>> +++ b/include/libc-symbols.h
>> @@ -352,6 +352,12 @@ for linking")
>>
>>   */
>>
>> +#ifdef HAVE_GNU_RETAIN
>> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
>> +#else
>> +# define attribute_used_retain __attribute__ ((__used__))
>> +#endif
>> +
>>   /* Symbol set support macros.  */
>>
>>   /* Make SYMBOL, which is in the text segment, an element of SET.  */
>> @@ -367,12 +373,12 @@ for linking")
>>   /* When building a shared library, make the set section writable,
>>      because it will need to be relocated at run time anyway.  */
>>   # define _elf_set_element(set, symbol) \
>> -  static const void *__elf_set_##set##_element_##symbol##__ \
>> -    __attribute__ ((used, section (#set))) = &(symbol)
>> +    static const void *__elf_set_##set##_element_##symbol##__ \
>> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>>   #else
>>   # define _elf_set_element(set, symbol) \
>> -  static const void *const __elf_set_##set##_element_##symbol##__ \
>> -    __attribute__ ((used, section (#set))) = &(symbol)
>> +    static const void *const __elf_set_##set##_element_##symbol##__ \
>> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>>   #endif
>>
>>   /* Define SET as a symbol set.  This may be required (it is in a.out) to
>> diff --git a/libio/Makefile b/libio/Makefile
>> index 12ce41038f..ad0d53bb49 100644
>> --- a/libio/Makefile
>> +++ b/libio/Makefile
>> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
>>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>>                  $(objpfx)tst-bz24228-mem.out
>>   endif
>> +
>> +tests += tst-cleanup-default tst-cleanup-default-static
>> +tests-static += tst-cleanup-default-static
>> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
>> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
>> +
>> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
>> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
>> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
>> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
>> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
>> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
>> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
>> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
>> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
>> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
>> +endif
>>   endif
>>
>>   include ../Rules
>> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>>   endif
>>
>> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-default-static.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>> +
>> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>
>Please add a separate .c file for each test to get the correct dependency.

This is unnecessary.

$(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c

does the work perfectly.

>> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>> +$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc-static.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-nostart-stop-gc-static.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>> +
>>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>>         $(common-objpfx)libio/; \
>> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
>> new file mode 100644
>> index 0000000000..837feac164
>> --- /dev/null
>> +++ b/libio/tst-cleanup.c
>> @@ -0,0 +1,34 @@
>> +/* Copyright (C) 2021 Free Software Foundation, Inc.
>> +   This file is part of the GNU C Library.
>> +
>> +   The GNU C Library is free software; you can redistribute it and/or
>> +   modify it under the terms of the GNU Lesser General Public
>> +   License as published by the Free Software Foundation; either
>> +   version 2.1 of the License, or (at your option) any later version.
>> +
>> +   The GNU C Library is distributed in the hope that it will be useful,
>> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> +   Lesser General Public License for more details.
>> +
>> +   You should have received a copy of the GNU Lesser General Public
>> +   License along with the GNU C Library; if not, see
>> +   <https://www.gnu.org/licenses/>.  */
>> +
>> +/* Test that stdout is flushed after atexit callbacks were run, even if the
>> + * executable is linked with --gc-sections.  */
>> +
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +
>> +void
>> +hook (void)
>> +{
>> +  puts ("hello");
>> +}
>> +
>> +int
>> +main (void)
>> +{
>> +  atexit (hook);
>> +}
>> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
>> new file mode 100644
>> index 0000000000..ce01362503
>> --- /dev/null
>> +++ b/libio/tst-cleanup.exp
>> @@ -0,0 +1 @@
>> +hello
>> --
>> 2.31.0.208.g409f899ff0-goog
>>
>
>
>-- 
>H.J.
  

On Fri, Apr 2, 2021 at 10:09 AM Fangrui Song <maskray@google.com> wrote:
>
> On 2021-04-02, H.J. Lu wrote:
> >On Thu, Apr 1, 2021 at 8:23 PM Fangrui Song <maskray@google.com> wrote:
> >>
> >> On 2021-04-01, H.J. Lu wrote:
> >> >On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song <maskray@google.com> wrote:
> >> >>
> >> >> So that text_set_element/data_set_element/bss_set_element defined
> >> >> variables will be retained by the linker.
> >> >>
> >> >> Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
> >> >> will not be optimized out; 'retain' prevents section garbage collection
> >> >> if the linker support SHF_GNU_RETAIN.
> >> >>
> >> >> GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
> >> >> identifier name sections to be GCed even if there are live
> >> >> __start_/__stop_ references.
> >> >>
> >> >> Without the change, there are some static linking problems, e.g.
> >> >> _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
> >> >> stdout is not flushed on exit.
> >> >>
> >> >> Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
> >> >> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
> >> >> ---
> >> >> Changes in v1 -> v2:
> >> >> * Define attribute_used_retain_section
> >> >> Changes in v2 -> v3:
> >> >> * Use attribute_used_retain instead attribute_used_retain_section
> >> >> Changes in v3 -> v4:
> >> >> * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
> >> >> Changes in v4 -> v5:
> >> >> * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
> >> >> * Rename *gcc_retain* to *gnu_retain*
> >> >> ---
> >> >>  config.h.in            |  3 +++
> >> >>  configure              | 59 ++++++++++++++++++++++++++++++++++++++++++
> >> >>  configure.ac           | 21 +++++++++++++++
> >> >>  include/libc-symbols.h | 14 +++++++---
> >> >>  libio/Makefile         | 32 +++++++++++++++++++++++
> >> >>  libio/tst-cleanup.c    | 33 +++++++++++++++++++++++
> >> >>  libio/tst-cleanup.exp  |  1 +
> >> >>  7 files changed, 159 insertions(+), 4 deletions(-)
> >> >>  create mode 100644 libio/tst-cleanup.c
> >> >>  create mode 100644 libio/tst-cleanup.exp
> >> >>
> >> >> diff --git a/config.h.in b/config.h.in
> >> >> index ca1547ae67..96a08c7757 100644
> >> >> --- a/config.h.in
> >> >> +++ b/config.h.in
> >> >> @@ -187,6 +187,9 @@
> >> >>  /* Define if gcc supports attribute ifunc.  */
> >> >>  #undef HAVE_GCC_IFUNC
> >> >>
> >> >> +/* Define if CC supports attribute retain.  */
> >> >> +#undef HAVE_GNU_RETAIN
> >> >> +
> >> >>  /* Define if the linker defines __ehdr_start.  */
> >> >>  #undef HAVE_EHDR_START
> >> >>
> >> >> diff --git a/configure b/configure
> >> >> index fcf43bf7de..e64b7f8efe 100755
> >> >> --- a/configure
> >> >> +++ b/configure
> >> >> @@ -4105,6 +4105,31 @@ fi
> >> >>  $as_echo "$libc_cv_textrel_ifunc" >&6; }
> >> >>
> >> >>
> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
> >> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
> >> >> +if ${libc_cv_gnu_retain+:} false; then :
> >> >> +  $as_echo_n "(cached) " >&6
> >> >> +else
> >> >> +  cat > conftest.c <<EOF
> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> +EOF
> >> >> +libc_cv_gnu_retain=no
> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> >> >> +   2>&5 ; then
> >> >> +  libc_cv_gnu_retain=yes
> >> >> +fi
> >> >> +rm -f conftest*
> >> >> +fi
> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
> >> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
> >> >> +
> >> >> +fi
> >> >> +config_vars="$config_vars
> >> >> +have-gnu-retain = $libc_cv_gnu_retain"
> >> >> +
> >> >>  # Check if gcc warns about alias for function with incompatible types.
> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
> >> >>  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
> >> >> @@ -5871,6 +5896,40 @@ fi
> >> >>  $as_echo "$libc_linker_feature" >&6; }
> >> >>
> >> >>
> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
> >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
> >> >> +libc_linker_feature=no
> >> >> +if test x"$gnu_ld" = x"yes"; then
> >> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
> >> >> +  if test -n "$libc_linker_check"; then
> >> >> +    cat > conftest.c <<EOF
> >> >> +int _start (void) { return 42; }
> >> >> +EOF
> >> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> >> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
> >> >> +                               -fPIC -shared -o conftest.so conftest.c
> >> >> +                               1>&5'
> >> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> >> >> +  (eval $ac_try) 2>&5
> >> >> +  ac_status=$?
> >> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> >> >> +  test $ac_status = 0; }; }
> >> >> +    then
> >> >> +      libc_linker_feature=yes
> >> >> +    fi
> >> >> +    rm -f conftest*
> >> >> +  fi
> >> >> +fi
> >> >> +if test $libc_linker_feature = yes; then
> >> >> +  libc_cv_z_start_stop_gc=yes
> >> >> +else
> >> >> +  libc_cv_z_start_stop_gc=no
> >> >> +fi
> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> >> >> +$as_echo "$libc_linker_feature" >&6; }
> >> >> +config_vars="$config_vars
> >> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
> >> >> +
> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
> >> >>  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
> >> >>  libc_linker_feature=no
> >> >> diff --git a/configure.ac b/configure.ac
> >> >> index fce967f2c2..cc47e56e82 100644
> >> >> --- a/configure.ac
> >> >> +++ b/configure.ac
> >> >> @@ -707,6 +707,23 @@ fi
> >> >>  rm -f conftest*])
> >> >>  AC_SUBST(libc_cv_textrel_ifunc)
> >> >>
> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> +AC_CACHE_CHECK([for GNU attribute retain support],
> >> >> +              libc_cv_gnu_retain, [dnl
> >> >> +cat > conftest.c <<EOF
> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> +EOF
> >> >> +libc_cv_gnu_retain=no
> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
> >> >> +   2>&AS_MESSAGE_LOG_FD ; then
> >> >> +  libc_cv_gnu_retain=yes
> >> >> +fi
> >> >> +rm -f conftest*])
> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
> >> >> +fi
> >> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
> >> >> +
> >> >>  # Check if gcc warns about alias for function with incompatible types.
> >> >>  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
> >> >>                libc_cv_gcc_incompatible_alias, [dnl
> >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
> >> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
> >> >>  AC_SUBST(libc_cv_z_execstack)
> >> >>
> >> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> >> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
> >> >> +
> >> >>  LIBC_LINKER_FEATURE([--no-dynamic-linker],
> >> >>                     [-Wl,--no-dynamic-linker],
> >> >>                     [libc_cv_no_dynamic_linker=yes],
> >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
> >> >> index 546fc26a7b..127ea656c2 100644
> >> >> --- a/include/libc-symbols.h
> >> >> +++ b/include/libc-symbols.h
> >> >> @@ -352,6 +352,12 @@ for linking")
> >> >>
> >> >>  */
> >> >>
> >> >> +#ifdef HAVE_GNU_RETAIN
> >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
> >> >> +#else
> >> >> +# define attribute_used_retain __attribute__ ((__used__))
> >> >> +#endif
> >> >> +
> >> >>  /* Symbol set support macros.  */
> >> >>
> >> >>  /* Make SYMBOL, which is in the text segment, an element of SET.  */
> >> >> @@ -367,12 +373,12 @@ for linking")
> >> >>  /* When building a shared library, make the set section writable,
> >> >>     because it will need to be relocated at run time anyway.  */
> >> >>  # define _elf_set_element(set, symbol) \
> >> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >>  #else
> >> >>  # define _elf_set_element(set, symbol) \
> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >>  #endif
> >> >>
> >> >>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
> >> >> diff --git a/libio/Makefile b/libio/Makefile
> >> >> index 12ce41038f..c9c232ebc2 100644
> >> >> --- a/libio/Makefile
> >> >> +++ b/libio/Makefile
> >> >> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared))
> >> >>  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
> >> >>                  $(objpfx)tst-bz24228-mem.out
> >> >>  endif
> >> >> +
> >> >> +tests += tst-cleanup-default
> >> >> +tests-static += tst-cleanup-default
> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out
> >> >
> >> >Please make 2 tests,  tst-cleanup-default and tst-cleanup-default-static.
> >>
> >> Added.
> >>
> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> >> >> +
> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> >> >> +tests-static += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
> >> >
> >> >Same here.
> >>
> >> Added.
> >>
> >> >> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc
> >> >> +endif
> >> >>  endif
> >> >>
> >> >>  include ../Rules
> >> >> @@ -224,6 +238,24 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >> >>  $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >> >>  endif
> >> >>
> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
> >> >> +       $(compile.c) -o $@
> >> >> +
> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> >> >> +       $(compile.c) -o $@
> >> >> +
> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
> >> >> +       $(compile.c) -o $@
> >> >>
> >> >>  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
> >> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
> >> >>         $(common-objpfx)libio/; \
> >> >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
> >> >> new file mode 100644
> >> >> index 0000000000..7f0a34a91e
> >> >> --- /dev/null
> >> >> +++ b/libio/tst-cleanup.c
> >> >> @@ -0,0 +1,33 @@
> >> >
> >> >Please add a comment saying that test --gc-sections.
> >>
> >> OK, added.
> >>
> >> >> +/* Copyright (C) 2021 Free Software Foundation, Inc.
> >> >> +   This file is part of the GNU C Library.
> >> >> +
> >> >> +   The GNU C Library is free software; you can redistribute it and/or
> >> >> +   modify it under the terms of the GNU Lesser General Public
> >> >> +   License as published by the Free Software Foundation; either
> >> >> +   version 2.1 of the License, or (at your option) any later version.
> >> >> +
> >> >> +   The GNU C Library is distributed in the hope that it will be useful,
> >> >> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> >> >> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> >> >> +   Lesser General Public License for more details.
> >> >> +
> >> >> +   You should have received a copy of the GNU Lesser General Public
> >> >> +   License along with the GNU C Library; if not, see
> >> >> +   <https://www.gnu.org/licenses/>.  */
> >> >> +
> >> >> +/* Test that stdout is flushed after atexit callbacks were run.  */
> >> >> +
> >> >> +#include <stdio.h>
> >> >> +#include <stdlib.h>
> >> >> +
> >> >> +void
> >> >> +hook (void)
> >> >> +{
> >> >> +  puts ("hello");
> >> >> +}
> >> >> +
> >> >> +int
> >> >> +main (void)
> >> >> +{
> >> >> +  atexit (hook);
> >> >> +}
> >> >> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
> >> >> new file mode 100644
> >> >> index 0000000000..ce01362503
> >> >> --- /dev/null
> >> >> +++ b/libio/tst-cleanup.exp
> >> >> @@ -0,0 +1 @@
> >> >> +hello
> >> >> --
> >> >> 2.31.0.291.g576ba9dcdaf-goog
> >> >>
> >> >
> >>
> >> diff --git a/config.h.in b/config.h.in
> >> index ca1547ae67..96a08c7757 100644
> >> --- a/config.h.in
> >> +++ b/config.h.in
> >> @@ -187,6 +187,9 @@
> >>   /* Define if gcc supports attribute ifunc.  */
> >>   #undef HAVE_GCC_IFUNC
> >>
> >> +/* Define if CC supports attribute retain.  */
> >> +#undef HAVE_GNU_RETAIN
> >> +
> >>   /* Define if the linker defines __ehdr_start.  */
> >>   #undef HAVE_EHDR_START
> >>
> >> diff --git a/configure b/configure
> >> index fcf43bf7de..e64b7f8efe 100755
> >> --- a/configure
> >> +++ b/configure
> >> @@ -4105,6 +4105,31 @@ fi
> >>   $as_echo "$libc_cv_textrel_ifunc" >&6; }
> >>
> >>
> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
> >> +if ${libc_cv_gnu_retain+:} false; then :
> >> +  $as_echo_n "(cached) " >&6
> >> +else
> >> +  cat > conftest.c <<EOF
> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> +EOF
> >> +libc_cv_gnu_retain=no
> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> >> +   2>&5 ; then
> >> +  libc_cv_gnu_retain=yes
> >> +fi
> >> +rm -f conftest*
> >> +fi
> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
> >> +if test $libc_cv_gnu_retain = yes; then
> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
> >> +
> >> +fi
> >> +config_vars="$config_vars
> >> +have-gnu-retain = $libc_cv_gnu_retain"
> >> +
> >>   # Check if gcc warns about alias for function with incompatible types.
> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
> >>   $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
> >> @@ -5871,6 +5896,40 @@ fi
> >>   $as_echo "$libc_linker_feature" >&6; }
> >>
> >>
> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
> >> +libc_linker_feature=no
> >> +if test x"$gnu_ld" = x"yes"; then
> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
> >> +  if test -n "$libc_linker_check"; then
> >> +    cat > conftest.c <<EOF
> >> +int _start (void) { return 42; }
> >> +EOF
> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
> >> +                               -fPIC -shared -o conftest.so conftest.c
> >> +                               1>&5'
> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> >> +  (eval $ac_try) 2>&5
> >> +  ac_status=$?
> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> >> +  test $ac_status = 0; }; }
> >> +    then
> >> +      libc_linker_feature=yes
> >> +    fi
> >> +    rm -f conftest*
> >> +  fi
> >> +fi
> >> +if test $libc_linker_feature = yes; then
> >> +  libc_cv_z_start_stop_gc=yes
> >> +else
> >> +  libc_cv_z_start_stop_gc=no
> >> +fi
> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> >> +$as_echo "$libc_linker_feature" >&6; }
> >> +config_vars="$config_vars
> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
> >> +
> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
> >>   $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
> >>   libc_linker_feature=no
> >> diff --git a/configure.ac b/configure.ac
> >> index fce967f2c2..cc47e56e82 100644
> >> --- a/configure.ac
> >> +++ b/configure.ac
> >> @@ -707,6 +707,23 @@ fi
> >>   rm -f conftest*])
> >>   AC_SUBST(libc_cv_textrel_ifunc)
> >>
> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> +AC_CACHE_CHECK([for GNU attribute retain support],
> >> +              libc_cv_gnu_retain, [dnl
> >> +cat > conftest.c <<EOF
> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> +EOF
> >> +libc_cv_gnu_retain=no
> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
> >> +   2>&AS_MESSAGE_LOG_FD ; then
> >> +  libc_cv_gnu_retain=yes
> >> +fi
> >> +rm -f conftest*])
> >> +if test $libc_cv_gnu_retain = yes; then
> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
> >> +fi
> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
> >> +
> >>   # Check if gcc warns about alias for function with incompatible types.
> >>   AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
> >>                libc_cv_gcc_incompatible_alias, [dnl
> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
> >>   AC_SUBST(libc_cv_z_execstack)
> >>
> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
> >> +
> >>   LIBC_LINKER_FEATURE([--no-dynamic-linker],
> >>                     [-Wl,--no-dynamic-linker],
> >>                     [libc_cv_no_dynamic_linker=yes],
> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
> >> index 546fc26a7b..127ea656c2 100644
> >> --- a/include/libc-symbols.h
> >> +++ b/include/libc-symbols.h
> >> @@ -352,6 +352,12 @@ for linking")
> >>
> >>   */
> >>
> >> +#ifdef HAVE_GNU_RETAIN
> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
> >> +#else
> >> +# define attribute_used_retain __attribute__ ((__used__))
> >> +#endif
> >> +
> >>   /* Symbol set support macros.  */
> >>
> >>   /* Make SYMBOL, which is in the text segment, an element of SET.  */
> >> @@ -367,12 +373,12 @@ for linking")
> >>   /* When building a shared library, make the set section writable,
> >>      because it will need to be relocated at run time anyway.  */
> >>   # define _elf_set_element(set, symbol) \
> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >>   #else
> >>   # define _elf_set_element(set, symbol) \
> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >>   #endif
> >>
> >>   /* Define SET as a symbol set.  This may be required (it is in a.out) to
> >> diff --git a/libio/Makefile b/libio/Makefile
> >> index 12ce41038f..ad0d53bb49 100644
> >> --- a/libio/Makefile
> >> +++ b/libio/Makefile
> >> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
> >>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
> >>                  $(objpfx)tst-bz24228-mem.out
> >>   endif
> >> +
> >> +tests += tst-cleanup-default tst-cleanup-default-static
> >> +tests-static += tst-cleanup-default-static
> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> >> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
> >> +
> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
> >> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
> >> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> >> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
> >> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
> >> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
> >> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
> >> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
> >> +endif
> >>   endif
> >>
> >>   include ../Rules
> >> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >>   endif
> >>
> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
> >> +       $(compile.c) -o $@
> >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-default-static.o: tst-cleanup.c
> >> +       $(compile.c) -o $@
> >> +
> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> >> +       $(compile.c) -o $@
> >> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c
> >> +       $(compile.c) -o $@
> >
> >Please add a separate .c file for each test to get the correct dependency.
>
> This is unnecessary.
>
> $(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c
>
> does the work perfectly.
>

What does tst-cleanup-start-stop-gc-static.o.d contain?
  

On 2021-04-02, H.J. Lu wrote:
>On Thu, Apr 1, 2021 at 8:23 PM Fangrui Song <maskray@google.com> wrote:
>>
>> On 2021-04-01, H.J. Lu wrote:
>> >On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song <maskray@google.com> wrote:
>> >>
>> >> So that text_set_element/data_set_element/bss_set_element defined
>> >> variables will be retained by the linker.
>> >>
>> >> Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
>> >> will not be optimized out; 'retain' prevents section garbage collection
>> >> if the linker support SHF_GNU_RETAIN.
>> >>
>> >> GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
>> >> identifier name sections to be GCed even if there are live
>> >> __start_/__stop_ references.
>> >>
>> >> Without the change, there are some static linking problems, e.g.
>> >> _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
>> >> stdout is not flushed on exit.
>> >>
>> >> Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
>> >> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
>> >> ---
>> >> Changes in v1 -> v2:
>> >> * Define attribute_used_retain_section
>> >> Changes in v2 -> v3:
>> >> * Use attribute_used_retain instead attribute_used_retain_section
>> >> Changes in v3 -> v4:
>> >> * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
>> >> Changes in v4 -> v5:
>> >> * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
>> >> * Rename *gcc_retain* to *gnu_retain*
>> >> ---
>> >>  config.h.in            |  3 +++
>> >>  configure              | 59 ++++++++++++++++++++++++++++++++++++++++++
>> >>  configure.ac           | 21 +++++++++++++++
>> >>  include/libc-symbols.h | 14 +++++++---
>> >>  libio/Makefile         | 32 +++++++++++++++++++++++
>> >>  libio/tst-cleanup.c    | 33 +++++++++++++++++++++++
>> >>  libio/tst-cleanup.exp  |  1 +
>> >>  7 files changed, 159 insertions(+), 4 deletions(-)
>> >>  create mode 100644 libio/tst-cleanup.c
>> >>  create mode 100644 libio/tst-cleanup.exp
>> >>
>> >> diff --git a/config.h.in b/config.h.in
>> >> index ca1547ae67..96a08c7757 100644
>> >> --- a/config.h.in
>> >> +++ b/config.h.in
>> >> @@ -187,6 +187,9 @@
>> >>  /* Define if gcc supports attribute ifunc.  */
>> >>  #undef HAVE_GCC_IFUNC
>> >>
>> >> +/* Define if CC supports attribute retain.  */
>> >> +#undef HAVE_GNU_RETAIN
>> >> +
>> >>  /* Define if the linker defines __ehdr_start.  */
>> >>  #undef HAVE_EHDR_START
>> >>
>> >> diff --git a/configure b/configure
>> >> index fcf43bf7de..e64b7f8efe 100755
>> >> --- a/configure
>> >> +++ b/configure
>> >> @@ -4105,6 +4105,31 @@ fi
>> >>  $as_echo "$libc_cv_textrel_ifunc" >&6; }
>> >>
>> >>
>> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
>> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
>> >> +if ${libc_cv_gnu_retain+:} false; then :
>> >> +  $as_echo_n "(cached) " >&6
>> >> +else
>> >> +  cat > conftest.c <<EOF
>> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> +EOF
>> >> +libc_cv_gnu_retain=no
>> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
>> >> +   2>&5 ; then
>> >> +  libc_cv_gnu_retain=yes
>> >> +fi
>> >> +rm -f conftest*
>> >> +fi
>> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
>> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
>> >> +if test $libc_cv_gnu_retain = yes; then
>> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
>> >> +
>> >> +fi
>> >> +config_vars="$config_vars
>> >> +have-gnu-retain = $libc_cv_gnu_retain"
>> >> +
>> >>  # Check if gcc warns about alias for function with incompatible types.
>> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
>> >>  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
>> >> @@ -5871,6 +5896,40 @@ fi
>> >>  $as_echo "$libc_linker_feature" >&6; }
>> >>
>> >>
>> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
>> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
>> >> +libc_linker_feature=no
>> >> +if test x"$gnu_ld" = x"yes"; then
>> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
>> >> +  if test -n "$libc_linker_check"; then
>> >> +    cat > conftest.c <<EOF
>> >> +int _start (void) { return 42; }
>> >> +EOF
>> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
>> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
>> >> +                               -fPIC -shared -o conftest.so conftest.c
>> >> +                               1>&5'
>> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
>> >> +  (eval $ac_try) 2>&5
>> >> +  ac_status=$?
>> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
>> >> +  test $ac_status = 0; }; }
>> >> +    then
>> >> +      libc_linker_feature=yes
>> >> +    fi
>> >> +    rm -f conftest*
>> >> +  fi
>> >> +fi
>> >> +if test $libc_linker_feature = yes; then
>> >> +  libc_cv_z_start_stop_gc=yes
>> >> +else
>> >> +  libc_cv_z_start_stop_gc=no
>> >> +fi
>> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
>> >> +$as_echo "$libc_linker_feature" >&6; }
>> >> +config_vars="$config_vars
>> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
>> >> +
>> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>> >>  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>> >>  libc_linker_feature=no
>> >> diff --git a/configure.ac b/configure.ac
>> >> index fce967f2c2..cc47e56e82 100644
>> >> --- a/configure.ac
>> >> +++ b/configure.ac
>> >> @@ -707,6 +707,23 @@ fi
>> >>  rm -f conftest*])
>> >>  AC_SUBST(libc_cv_textrel_ifunc)
>> >>
>> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> +AC_CACHE_CHECK([for GNU attribute retain support],
>> >> +              libc_cv_gnu_retain, [dnl
>> >> +cat > conftest.c <<EOF
>> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> +EOF
>> >> +libc_cv_gnu_retain=no
>> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
>> >> +   2>&AS_MESSAGE_LOG_FD ; then
>> >> +  libc_cv_gnu_retain=yes
>> >> +fi
>> >> +rm -f conftest*])
>> >> +if test $libc_cv_gnu_retain = yes; then
>> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
>> >> +fi
>> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
>> >> +
>> >>  # Check if gcc warns about alias for function with incompatible types.
>> >>  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>> >>                libc_cv_gcc_incompatible_alias, [dnl
>> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>> >>  AC_SUBST(libc_cv_z_execstack)
>> >>
>> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
>> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
>> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
>> >> +
>> >>  LIBC_LINKER_FEATURE([--no-dynamic-linker],
>> >>                     [-Wl,--no-dynamic-linker],
>> >>                     [libc_cv_no_dynamic_linker=yes],
>> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
>> >> index 546fc26a7b..127ea656c2 100644
>> >> --- a/include/libc-symbols.h
>> >> +++ b/include/libc-symbols.h
>> >> @@ -352,6 +352,12 @@ for linking")
>> >>
>> >>  */
>> >>
>> >> +#ifdef HAVE_GNU_RETAIN
>> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
>> >> +#else
>> >> +# define attribute_used_retain __attribute__ ((__used__))
>> >> +#endif
>> >> +
>> >>  /* Symbol set support macros.  */
>> >>
>> >>  /* Make SYMBOL, which is in the text segment, an element of SET.  */
>> >> @@ -367,12 +373,12 @@ for linking")
>> >>  /* When building a shared library, make the set section writable,
>> >>     because it will need to be relocated at run time anyway.  */
>> >>  # define _elf_set_element(set, symbol) \
>> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
>> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
>> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >>  #else
>> >>  # define _elf_set_element(set, symbol) \
>> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >>  #endif
>> >>
>> >>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
>> >> diff --git a/libio/Makefile b/libio/Makefile
>> >> index 12ce41038f..c9c232ebc2 100644
>> >> --- a/libio/Makefile
>> >> +++ b/libio/Makefile
>> >> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared))
>> >>  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>> >>                  $(objpfx)tst-bz24228-mem.out
>> >>  endif
>> >> +
>> >> +tests += tst-cleanup-default
>> >> +tests-static += tst-cleanup-default
>> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out
>> >
>> >Please make 2 tests,  tst-cleanup-default and tst-cleanup-default-static.
>>
>> Added.
>>
>> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> >> +
>> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
>> >> +tests-static += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
>> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
>> >
>> >Same here.
>>
>> Added.
>>
>> >> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
>> >> +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc
>> >> +endif
>> >>  endif
>> >>
>> >>  include ../Rules
>> >> @@ -224,6 +238,24 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>> >>  $(objpfx)tst-wfile-sync.out: $(gen-locales)
>> >>  endif
>> >>
>> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
>> >> +       $(compile.c) -o $@
>> >> +
>> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> >> +       $(compile.c) -o $@
>> >> +
>> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
>> >> +       $(compile.c) -o $@
>> >>
>> >>  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>> >>         $(common-objpfx)libio/; \
>> >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
>> >> new file mode 100644
>> >> index 0000000000..7f0a34a91e
>> >> --- /dev/null
>> >> +++ b/libio/tst-cleanup.c
>> >> @@ -0,0 +1,33 @@
>> >
>> >Please add a comment saying that test --gc-sections.
>>
>> OK, added.
>>
>> >> +/* Copyright (C) 2021 Free Software Foundation, Inc.
>> >> +   This file is part of the GNU C Library.
>> >> +
>> >> +   The GNU C Library is free software; you can redistribute it and/or
>> >> +   modify it under the terms of the GNU Lesser General Public
>> >> +   License as published by the Free Software Foundation; either
>> >> +   version 2.1 of the License, or (at your option) any later version.
>> >> +
>> >> +   The GNU C Library is distributed in the hope that it will be useful,
>> >> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>> >> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> >> +   Lesser General Public License for more details.
>> >> +
>> >> +   You should have received a copy of the GNU Lesser General Public
>> >> +   License along with the GNU C Library; if not, see
>> >> +   <https://www.gnu.org/licenses/>.  */
>> >> +
>> >> +/* Test that stdout is flushed after atexit callbacks were run.  */
>> >> +
>> >> +#include <stdio.h>
>> >> +#include <stdlib.h>
>> >> +
>> >> +void
>> >> +hook (void)
>> >> +{
>> >> +  puts ("hello");
>> >> +}
>> >> +
>> >> +int
>> >> +main (void)
>> >> +{
>> >> +  atexit (hook);
>> >> +}
>> >> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
>> >> new file mode 100644
>> >> index 0000000000..ce01362503
>> >> --- /dev/null
>> >> +++ b/libio/tst-cleanup.exp
>> >> @@ -0,0 +1 @@
>> >> +hello
>> >> --
>> >> 2.31.0.291.g576ba9dcdaf-goog
>> >>
>> >
>>
>> diff --git a/config.h.in b/config.h.in
>> index ca1547ae67..96a08c7757 100644
>> --- a/config.h.in
>> +++ b/config.h.in
>> @@ -187,6 +187,9 @@
>>   /* Define if gcc supports attribute ifunc.  */
>>   #undef HAVE_GCC_IFUNC
>>
>> +/* Define if CC supports attribute retain.  */
>> +#undef HAVE_GNU_RETAIN
>> +
>>   /* Define if the linker defines __ehdr_start.  */
>>   #undef HAVE_EHDR_START
>>
>> diff --git a/configure b/configure
>> index fcf43bf7de..e64b7f8efe 100755
>> --- a/configure
>> +++ b/configure
>> @@ -4105,6 +4105,31 @@ fi
>>   $as_echo "$libc_cv_textrel_ifunc" >&6; }
>>
>>
>> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
>> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
>> +if ${libc_cv_gnu_retain+:} false; then :
>> +  $as_echo_n "(cached) " >&6
>> +else
>> +  cat > conftest.c <<EOF
>> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> +EOF
>> +libc_cv_gnu_retain=no
>> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
>> +   2>&5 ; then
>> +  libc_cv_gnu_retain=yes
>> +fi
>> +rm -f conftest*
>> +fi
>> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
>> +$as_echo "$libc_cv_gnu_retain" >&6; }
>> +if test $libc_cv_gnu_retain = yes; then
>> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
>> +
>> +fi
>> +config_vars="$config_vars
>> +have-gnu-retain = $libc_cv_gnu_retain"
>> +
>>   # Check if gcc warns about alias for function with incompatible types.
>>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
>>   $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
>> @@ -5871,6 +5896,40 @@ fi
>>   $as_echo "$libc_linker_feature" >&6; }
>>
>>
>> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
>> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
>> +libc_linker_feature=no
>> +if test x"$gnu_ld" = x"yes"; then
>> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
>> +  if test -n "$libc_linker_check"; then
>> +    cat > conftest.c <<EOF
>> +int _start (void) { return 42; }
>> +EOF
>> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
>> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
>> +                               -fPIC -shared -o conftest.so conftest.c
>> +                               1>&5'
>> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
>> +  (eval $ac_try) 2>&5
>> +  ac_status=$?
>> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
>> +  test $ac_status = 0; }; }
>> +    then
>> +      libc_linker_feature=yes
>> +    fi
>> +    rm -f conftest*
>> +  fi
>> +fi
>> +if test $libc_linker_feature = yes; then
>> +  libc_cv_z_start_stop_gc=yes
>> +else
>> +  libc_cv_z_start_stop_gc=no
>> +fi
>> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
>> +$as_echo "$libc_linker_feature" >&6; }
>> +config_vars="$config_vars
>> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
>> +
>>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>>   $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>>   libc_linker_feature=no
>> diff --git a/configure.ac b/configure.ac
>> index fce967f2c2..cc47e56e82 100644
>> --- a/configure.ac
>> +++ b/configure.ac
>> @@ -707,6 +707,23 @@ fi
>>   rm -f conftest*])
>>   AC_SUBST(libc_cv_textrel_ifunc)
>>
>> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> +AC_CACHE_CHECK([for GNU attribute retain support],
>> +              libc_cv_gnu_retain, [dnl
>> +cat > conftest.c <<EOF
>> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> +EOF
>> +libc_cv_gnu_retain=no
>> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
>> +   2>&AS_MESSAGE_LOG_FD ; then
>> +  libc_cv_gnu_retain=yes
>> +fi
>> +rm -f conftest*])
>> +if test $libc_cv_gnu_retain = yes; then
>> +  AC_DEFINE(HAVE_GNU_RETAIN)
>> +fi
>> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
>> +
>>   # Check if gcc warns about alias for function with incompatible types.
>>   AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>>                libc_cv_gcc_incompatible_alias, [dnl
>> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>>   AC_SUBST(libc_cv_z_execstack)
>>
>> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
>> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
>> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
>> +
>>   LIBC_LINKER_FEATURE([--no-dynamic-linker],
>>                     [-Wl,--no-dynamic-linker],
>>                     [libc_cv_no_dynamic_linker=yes],
>> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
>> index 546fc26a7b..127ea656c2 100644
>> --- a/include/libc-symbols.h
>> +++ b/include/libc-symbols.h
>> @@ -352,6 +352,12 @@ for linking")
>>
>>   */
>>
>> +#ifdef HAVE_GNU_RETAIN
>> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
>> +#else
>> +# define attribute_used_retain __attribute__ ((__used__))
>> +#endif
>> +
>>   /* Symbol set support macros.  */
>>
>>   /* Make SYMBOL, which is in the text segment, an element of SET.  */
>> @@ -367,12 +373,12 @@ for linking")
>>   /* When building a shared library, make the set section writable,
>>      because it will need to be relocated at run time anyway.  */
>>   # define _elf_set_element(set, symbol) \
>> -  static const void *__elf_set_##set##_element_##symbol##__ \
>> -    __attribute__ ((used, section (#set))) = &(symbol)
>> +    static const void *__elf_set_##set##_element_##symbol##__ \
>> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>>   #else
>>   # define _elf_set_element(set, symbol) \
>> -  static const void *const __elf_set_##set##_element_##symbol##__ \
>> -    __attribute__ ((used, section (#set))) = &(symbol)
>> +    static const void *const __elf_set_##set##_element_##symbol##__ \
>> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>>   #endif
>>
>>   /* Define SET as a symbol set.  This may be required (it is in a.out) to
>> diff --git a/libio/Makefile b/libio/Makefile
>> index 12ce41038f..ad0d53bb49 100644
>> --- a/libio/Makefile
>> +++ b/libio/Makefile
>> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
>>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>>                  $(objpfx)tst-bz24228-mem.out
>>   endif
>> +
>> +tests += tst-cleanup-default tst-cleanup-default-static
>> +tests-static += tst-cleanup-default-static
>> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
>> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
>> +
>> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
>> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
>> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
>> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
>> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
>> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
>> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
>> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
>> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
>> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
>> +endif
>>   endif
>>
>>   include ../Rules
>> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>>   endif
>>
>> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-default-static.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>> +
>> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>
>Please add a separate .c file for each test to get the correct dependency.

Changed this block to:

@@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
  $(objpfx)tst-wfile-sync.out: $(gen-locales)
  endif
  
+$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
+	cmp $^ > $@; \
+	$(evaluate-test)
+$(objpfx)tst-cleanup-default.c: tst-cleanup.c
+	cp $< $@
+$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
+	cmp $^ > $@; \
+	$(evaluate-test)
+$(objpfx)tst-cleanup-default-static.c: tst-cleanup.c
+	cp $< $@
+
+$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
+	cmp $^ > $@; \
+	$(evaluate-test)
+$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
+	$(compile.c) -o $@
+$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
+	cmp $^ > $@; \
+	$(evaluate-test)
+$(objpfx)tst-cleanup-start-stop-gc-static.c: tst-cleanup.c
+	cp $< $@
+
+$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
+	cmp $^ > $@; \
+	$(evaluate-test)
+$(objpfx)tst-cleanup-nostart-stop-gc.c: tst-cleanup.c
+	cp $< $@
+$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc-static.out
+	cmp $^ > $@; \
+	$(evaluate-test)
+$(objpfx)tst-cleanup-nostart-stop-gc-static.c: tst-cleanup.c
+	cp $< $@
+
  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
  	$(SHELL) $< $(common-objpfx) '$(test-program-prefix)'	\
  	$(common-objpfx)libio/; \

>> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>> +$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc-static.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-nostart-stop-gc-static.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>> +
>>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>>         $(common-objpfx)libio/; \
>> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
>> new file mode 100644
>> index 0000000000..837feac164
>> --- /dev/null
>> +++ b/libio/tst-cleanup.c
>> @@ -0,0 +1,34 @@
>> +/* Copyright (C) 2021 Free Software Foundation, Inc.
>> +   This file is part of the GNU C Library.
>> +
>> +   The GNU C Library is free software; you can redistribute it and/or
>> +   modify it under the terms of the GNU Lesser General Public
>> +   License as published by the Free Software Foundation; either
>> +   version 2.1 of the License, or (at your option) any later version.
>> +
>> +   The GNU C Library is distributed in the hope that it will be useful,
>> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> +   Lesser General Public License for more details.
>> +
>> +   You should have received a copy of the GNU Lesser General Public
>> +   License along with the GNU C Library; if not, see
>> +   <https://www.gnu.org/licenses/>.  */
>> +
>> +/* Test that stdout is flushed after atexit callbacks were run, even if the
>> + * executable is linked with --gc-sections.  */
>> +
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +
>> +void
>> +hook (void)
>> +{
>> +  puts ("hello");
>> +}
>> +
>> +int
>> +main (void)
>> +{
>> +  atexit (hook);
>> +}
>> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
>> new file mode 100644
>> index 0000000000..ce01362503
>> --- /dev/null
>> +++ b/libio/tst-cleanup.exp
>> @@ -0,0 +1 @@
>> +hello
>> --
>> 2.31.0.208.g409f899ff0-goog
>>
>
>
>-- 
>H.J.
  

On Sat, Apr 3, 2021 at 11:02 AM Fangrui Song <maskray@google.com> wrote:
>
>
> On 2021-04-02, H.J. Lu wrote:
> >On Thu, Apr 1, 2021 at 8:23 PM Fangrui Song <maskray@google.com> wrote:
> >>
> >> On 2021-04-01, H.J. Lu wrote:
> >> >On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song <maskray@google.com> wrote:
> >> >>
> >> >> So that text_set_element/data_set_element/bss_set_element defined
> >> >> variables will be retained by the linker.
> >> >>
> >> >> Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
> >> >> will not be optimized out; 'retain' prevents section garbage collection
> >> >> if the linker support SHF_GNU_RETAIN.
> >> >>
> >> >> GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
> >> >> identifier name sections to be GCed even if there are live
> >> >> __start_/__stop_ references.
> >> >>
> >> >> Without the change, there are some static linking problems, e.g.
> >> >> _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
> >> >> stdout is not flushed on exit.
> >> >>
> >> >> Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
> >> >> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
> >> >> ---
> >> >> Changes in v1 -> v2:
> >> >> * Define attribute_used_retain_section
> >> >> Changes in v2 -> v3:
> >> >> * Use attribute_used_retain instead attribute_used_retain_section
> >> >> Changes in v3 -> v4:
> >> >> * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
> >> >> Changes in v4 -> v5:
> >> >> * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
> >> >> * Rename *gcc_retain* to *gnu_retain*
> >> >> ---
> >> >>  config.h.in            |  3 +++
> >> >>  configure              | 59 ++++++++++++++++++++++++++++++++++++++++++
> >> >>  configure.ac           | 21 +++++++++++++++
> >> >>  include/libc-symbols.h | 14 +++++++---
> >> >>  libio/Makefile         | 32 +++++++++++++++++++++++
> >> >>  libio/tst-cleanup.c    | 33 +++++++++++++++++++++++
> >> >>  libio/tst-cleanup.exp  |  1 +
> >> >>  7 files changed, 159 insertions(+), 4 deletions(-)
> >> >>  create mode 100644 libio/tst-cleanup.c
> >> >>  create mode 100644 libio/tst-cleanup.exp
> >> >>
> >> >> diff --git a/config.h.in b/config.h.in
> >> >> index ca1547ae67..96a08c7757 100644
> >> >> --- a/config.h.in
> >> >> +++ b/config.h.in
> >> >> @@ -187,6 +187,9 @@
> >> >>  /* Define if gcc supports attribute ifunc.  */
> >> >>  #undef HAVE_GCC_IFUNC
> >> >>
> >> >> +/* Define if CC supports attribute retain.  */
> >> >> +#undef HAVE_GNU_RETAIN
> >> >> +
> >> >>  /* Define if the linker defines __ehdr_start.  */
> >> >>  #undef HAVE_EHDR_START
> >> >>
> >> >> diff --git a/configure b/configure
> >> >> index fcf43bf7de..e64b7f8efe 100755
> >> >> --- a/configure
> >> >> +++ b/configure
> >> >> @@ -4105,6 +4105,31 @@ fi
> >> >>  $as_echo "$libc_cv_textrel_ifunc" >&6; }
> >> >>
> >> >>
> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
> >> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
> >> >> +if ${libc_cv_gnu_retain+:} false; then :
> >> >> +  $as_echo_n "(cached) " >&6
> >> >> +else
> >> >> +  cat > conftest.c <<EOF
> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> +EOF
> >> >> +libc_cv_gnu_retain=no
> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> >> >> +   2>&5 ; then
> >> >> +  libc_cv_gnu_retain=yes
> >> >> +fi
> >> >> +rm -f conftest*
> >> >> +fi
> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
> >> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
> >> >> +
> >> >> +fi
> >> >> +config_vars="$config_vars
> >> >> +have-gnu-retain = $libc_cv_gnu_retain"
> >> >> +
> >> >>  # Check if gcc warns about alias for function with incompatible types.
> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
> >> >>  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
> >> >> @@ -5871,6 +5896,40 @@ fi
> >> >>  $as_echo "$libc_linker_feature" >&6; }
> >> >>
> >> >>
> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
> >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
> >> >> +libc_linker_feature=no
> >> >> +if test x"$gnu_ld" = x"yes"; then
> >> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
> >> >> +  if test -n "$libc_linker_check"; then
> >> >> +    cat > conftest.c <<EOF
> >> >> +int _start (void) { return 42; }
> >> >> +EOF
> >> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> >> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
> >> >> +                               -fPIC -shared -o conftest.so conftest.c
> >> >> +                               1>&5'
> >> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> >> >> +  (eval $ac_try) 2>&5
> >> >> +  ac_status=$?
> >> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> >> >> +  test $ac_status = 0; }; }
> >> >> +    then
> >> >> +      libc_linker_feature=yes
> >> >> +    fi
> >> >> +    rm -f conftest*
> >> >> +  fi
> >> >> +fi
> >> >> +if test $libc_linker_feature = yes; then
> >> >> +  libc_cv_z_start_stop_gc=yes
> >> >> +else
> >> >> +  libc_cv_z_start_stop_gc=no
> >> >> +fi
> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> >> >> +$as_echo "$libc_linker_feature" >&6; }
> >> >> +config_vars="$config_vars
> >> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
> >> >> +
> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
> >> >>  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
> >> >>  libc_linker_feature=no
> >> >> diff --git a/configure.ac b/configure.ac
> >> >> index fce967f2c2..cc47e56e82 100644
> >> >> --- a/configure.ac
> >> >> +++ b/configure.ac
> >> >> @@ -707,6 +707,23 @@ fi
> >> >>  rm -f conftest*])
> >> >>  AC_SUBST(libc_cv_textrel_ifunc)
> >> >>
> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> +AC_CACHE_CHECK([for GNU attribute retain support],
> >> >> +              libc_cv_gnu_retain, [dnl
> >> >> +cat > conftest.c <<EOF
> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> +EOF
> >> >> +libc_cv_gnu_retain=no
> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
> >> >> +   2>&AS_MESSAGE_LOG_FD ; then
> >> >> +  libc_cv_gnu_retain=yes
> >> >> +fi
> >> >> +rm -f conftest*])
> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
> >> >> +fi
> >> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
> >> >> +
> >> >>  # Check if gcc warns about alias for function with incompatible types.
> >> >>  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
> >> >>                libc_cv_gcc_incompatible_alias, [dnl
> >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
> >> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
> >> >>  AC_SUBST(libc_cv_z_execstack)
> >> >>
> >> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> >> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
> >> >> +
> >> >>  LIBC_LINKER_FEATURE([--no-dynamic-linker],
> >> >>                     [-Wl,--no-dynamic-linker],
> >> >>                     [libc_cv_no_dynamic_linker=yes],
> >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
> >> >> index 546fc26a7b..127ea656c2 100644
> >> >> --- a/include/libc-symbols.h
> >> >> +++ b/include/libc-symbols.h
> >> >> @@ -352,6 +352,12 @@ for linking")
> >> >>
> >> >>  */
> >> >>
> >> >> +#ifdef HAVE_GNU_RETAIN
> >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
> >> >> +#else
> >> >> +# define attribute_used_retain __attribute__ ((__used__))
> >> >> +#endif
> >> >> +
> >> >>  /* Symbol set support macros.  */
> >> >>
> >> >>  /* Make SYMBOL, which is in the text segment, an element of SET.  */
> >> >> @@ -367,12 +373,12 @@ for linking")
> >> >>  /* When building a shared library, make the set section writable,
> >> >>     because it will need to be relocated at run time anyway.  */
> >> >>  # define _elf_set_element(set, symbol) \
> >> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >>  #else
> >> >>  # define _elf_set_element(set, symbol) \
> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >>  #endif
> >> >>
> >> >>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
> >> >> diff --git a/libio/Makefile b/libio/Makefile
> >> >> index 12ce41038f..c9c232ebc2 100644
> >> >> --- a/libio/Makefile
> >> >> +++ b/libio/Makefile
> >> >> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared))
> >> >>  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
> >> >>                  $(objpfx)tst-bz24228-mem.out
> >> >>  endif
> >> >> +
> >> >> +tests += tst-cleanup-default
> >> >> +tests-static += tst-cleanup-default
> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out
> >> >
> >> >Please make 2 tests,  tst-cleanup-default and tst-cleanup-default-static.
> >>
> >> Added.
> >>
> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> >> >> +
> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> >> >> +tests-static += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
> >> >
> >> >Same here.
> >>
> >> Added.
> >>
> >> >> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc
> >> >> +endif
> >> >>  endif
> >> >>
> >> >>  include ../Rules
> >> >> @@ -224,6 +238,24 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >> >>  $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >> >>  endif
> >> >>
> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
> >> >> +       $(compile.c) -o $@
> >> >> +
> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> >> >> +       $(compile.c) -o $@
> >> >> +
> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
> >> >> +       $(compile.c) -o $@
> >> >>
> >> >>  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
> >> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
> >> >>         $(common-objpfx)libio/; \
> >> >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
> >> >> new file mode 100644
> >> >> index 0000000000..7f0a34a91e
> >> >> --- /dev/null
> >> >> +++ b/libio/tst-cleanup.c
> >> >> @@ -0,0 +1,33 @@
> >> >
> >> >Please add a comment saying that test --gc-sections.
> >>
> >> OK, added.
> >>
> >> >> +/* Copyright (C) 2021 Free Software Foundation, Inc.
> >> >> +   This file is part of the GNU C Library.
> >> >> +
> >> >> +   The GNU C Library is free software; you can redistribute it and/or
> >> >> +   modify it under the terms of the GNU Lesser General Public
> >> >> +   License as published by the Free Software Foundation; either
> >> >> +   version 2.1 of the License, or (at your option) any later version.
> >> >> +
> >> >> +   The GNU C Library is distributed in the hope that it will be useful,
> >> >> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> >> >> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> >> >> +   Lesser General Public License for more details.
> >> >> +
> >> >> +   You should have received a copy of the GNU Lesser General Public
> >> >> +   License along with the GNU C Library; if not, see
> >> >> +   <https://www.gnu.org/licenses/>.  */
> >> >> +
> >> >> +/* Test that stdout is flushed after atexit callbacks were run.  */
> >> >> +
> >> >> +#include <stdio.h>
> >> >> +#include <stdlib.h>
> >> >> +
> >> >> +void
> >> >> +hook (void)
> >> >> +{
> >> >> +  puts ("hello");
> >> >> +}
> >> >> +
> >> >> +int
> >> >> +main (void)
> >> >> +{
> >> >> +  atexit (hook);
> >> >> +}
> >> >> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
> >> >> new file mode 100644
> >> >> index 0000000000..ce01362503
> >> >> --- /dev/null
> >> >> +++ b/libio/tst-cleanup.exp
> >> >> @@ -0,0 +1 @@
> >> >> +hello
> >> >> --
> >> >> 2.31.0.291.g576ba9dcdaf-goog
> >> >>
> >> >
> >>
> >> diff --git a/config.h.in b/config.h.in
> >> index ca1547ae67..96a08c7757 100644
> >> --- a/config.h.in
> >> +++ b/config.h.in
> >> @@ -187,6 +187,9 @@
> >>   /* Define if gcc supports attribute ifunc.  */
> >>   #undef HAVE_GCC_IFUNC
> >>
> >> +/* Define if CC supports attribute retain.  */
> >> +#undef HAVE_GNU_RETAIN
> >> +
> >>   /* Define if the linker defines __ehdr_start.  */
> >>   #undef HAVE_EHDR_START
> >>
> >> diff --git a/configure b/configure
> >> index fcf43bf7de..e64b7f8efe 100755
> >> --- a/configure
> >> +++ b/configure
> >> @@ -4105,6 +4105,31 @@ fi
> >>   $as_echo "$libc_cv_textrel_ifunc" >&6; }
> >>
> >>
> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
> >> +if ${libc_cv_gnu_retain+:} false; then :
> >> +  $as_echo_n "(cached) " >&6
> >> +else
> >> +  cat > conftest.c <<EOF
> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> +EOF
> >> +libc_cv_gnu_retain=no
> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> >> +   2>&5 ; then
> >> +  libc_cv_gnu_retain=yes
> >> +fi
> >> +rm -f conftest*
> >> +fi
> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
> >> +if test $libc_cv_gnu_retain = yes; then
> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
> >> +
> >> +fi
> >> +config_vars="$config_vars
> >> +have-gnu-retain = $libc_cv_gnu_retain"
> >> +
> >>   # Check if gcc warns about alias for function with incompatible types.
> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
> >>   $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
> >> @@ -5871,6 +5896,40 @@ fi
> >>   $as_echo "$libc_linker_feature" >&6; }
> >>
> >>
> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
> >> +libc_linker_feature=no
> >> +if test x"$gnu_ld" = x"yes"; then
> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
> >> +  if test -n "$libc_linker_check"; then
> >> +    cat > conftest.c <<EOF
> >> +int _start (void) { return 42; }
> >> +EOF
> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
> >> +                               -fPIC -shared -o conftest.so conftest.c
> >> +                               1>&5'
> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> >> +  (eval $ac_try) 2>&5
> >> +  ac_status=$?
> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> >> +  test $ac_status = 0; }; }
> >> +    then
> >> +      libc_linker_feature=yes
> >> +    fi
> >> +    rm -f conftest*
> >> +  fi
> >> +fi
> >> +if test $libc_linker_feature = yes; then
> >> +  libc_cv_z_start_stop_gc=yes
> >> +else
> >> +  libc_cv_z_start_stop_gc=no
> >> +fi
> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> >> +$as_echo "$libc_linker_feature" >&6; }
> >> +config_vars="$config_vars
> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
> >> +
> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
> >>   $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
> >>   libc_linker_feature=no
> >> diff --git a/configure.ac b/configure.ac
> >> index fce967f2c2..cc47e56e82 100644
> >> --- a/configure.ac
> >> +++ b/configure.ac
> >> @@ -707,6 +707,23 @@ fi
> >>   rm -f conftest*])
> >>   AC_SUBST(libc_cv_textrel_ifunc)
> >>
> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> +AC_CACHE_CHECK([for GNU attribute retain support],
> >> +              libc_cv_gnu_retain, [dnl
> >> +cat > conftest.c <<EOF
> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> +EOF
> >> +libc_cv_gnu_retain=no
> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
> >> +   2>&AS_MESSAGE_LOG_FD ; then
> >> +  libc_cv_gnu_retain=yes
> >> +fi
> >> +rm -f conftest*])
> >> +if test $libc_cv_gnu_retain = yes; then
> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
> >> +fi
> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
> >> +
> >>   # Check if gcc warns about alias for function with incompatible types.
> >>   AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
> >>                libc_cv_gcc_incompatible_alias, [dnl
> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
> >>   AC_SUBST(libc_cv_z_execstack)
> >>
> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
> >> +
> >>   LIBC_LINKER_FEATURE([--no-dynamic-linker],
> >>                     [-Wl,--no-dynamic-linker],
> >>                     [libc_cv_no_dynamic_linker=yes],
> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
> >> index 546fc26a7b..127ea656c2 100644
> >> --- a/include/libc-symbols.h
> >> +++ b/include/libc-symbols.h
> >> @@ -352,6 +352,12 @@ for linking")
> >>
> >>   */
> >>
> >> +#ifdef HAVE_GNU_RETAIN
> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
> >> +#else
> >> +# define attribute_used_retain __attribute__ ((__used__))
> >> +#endif
> >> +
> >>   /* Symbol set support macros.  */
> >>
> >>   /* Make SYMBOL, which is in the text segment, an element of SET.  */
> >> @@ -367,12 +373,12 @@ for linking")
> >>   /* When building a shared library, make the set section writable,
> >>      because it will need to be relocated at run time anyway.  */
> >>   # define _elf_set_element(set, symbol) \
> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >>   #else
> >>   # define _elf_set_element(set, symbol) \
> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >>   #endif
> >>
> >>   /* Define SET as a symbol set.  This may be required (it is in a.out) to
> >> diff --git a/libio/Makefile b/libio/Makefile
> >> index 12ce41038f..ad0d53bb49 100644
> >> --- a/libio/Makefile
> >> +++ b/libio/Makefile
> >> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
> >>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
> >>                  $(objpfx)tst-bz24228-mem.out
> >>   endif
> >> +
> >> +tests += tst-cleanup-default tst-cleanup-default-static
> >> +tests-static += tst-cleanup-default-static
> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> >> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
> >> +
> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
> >> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
> >> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> >> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
> >> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
> >> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
> >> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
> >> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
> >> +endif
> >>   endif
> >>
> >>   include ../Rules
> >> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >>   endif
> >>
> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
> >> +       $(compile.c) -o $@
> >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-default-static.o: tst-cleanup.c
> >> +       $(compile.c) -o $@
> >> +
> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> >> +       $(compile.c) -o $@
> >> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c
> >> +       $(compile.c) -o $@
> >
> >Please add a separate .c file for each test to get the correct dependency.
>
> Changed this block to:
>
> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>   endif
>
> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> +       cmp $^ > $@; \
> +       $(evaluate-test)
> +$(objpfx)tst-cleanup-default.c: tst-cleanup.c
> +       cp $< $@
> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
> +       cmp $^ > $@; \
> +       $(evaluate-test)
> +$(objpfx)tst-cleanup-default-static.c: tst-cleanup.c
> +       cp $< $@
> +
> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> +       cmp $^ > $@; \
> +       $(evaluate-test)
> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> +       $(compile.c) -o $@
> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
> +       cmp $^ > $@; \
> +       $(evaluate-test)
> +$(objpfx)tst-cleanup-start-stop-gc-static.c: tst-cleanup.c
> +       cp $< $@
> +
> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
> +       cmp $^ > $@; \
> +       $(evaluate-test)
> +$(objpfx)tst-cleanup-nostart-stop-gc.c: tst-cleanup.c
> +       cp $< $@
> +$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc-static.out
> +       cmp $^ > $@; \
> +       $(evaluate-test)
> +$(objpfx)tst-cleanup-nostart-stop-gc-static.c: tst-cleanup.c
> +       cp $< $@
> +
>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>         $(common-objpfx)libio/; \
>

"make clean" doesn't remove the generated files. The standard way in glibc
is to add a *-static.c source.
  

On 2021-04-03, H.J. Lu wrote:
>On Sat, Apr 3, 2021 at 11:02 AM Fangrui Song <maskray@google.com> wrote:
>>
>>
>> On 2021-04-02, H.J. Lu wrote:
>> >On Thu, Apr 1, 2021 at 8:23 PM Fangrui Song <maskray@google.com> wrote:
>> >>
>> >> On 2021-04-01, H.J. Lu wrote:
>> >> >On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song <maskray@google.com> wrote:
>> >> >>
>> >> >> So that text_set_element/data_set_element/bss_set_element defined
>> >> >> variables will be retained by the linker.
>> >> >>
>> >> >> Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
>> >> >> will not be optimized out; 'retain' prevents section garbage collection
>> >> >> if the linker support SHF_GNU_RETAIN.
>> >> >>
>> >> >> GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
>> >> >> identifier name sections to be GCed even if there are live
>> >> >> __start_/__stop_ references.
>> >> >>
>> >> >> Without the change, there are some static linking problems, e.g.
>> >> >> _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
>> >> >> stdout is not flushed on exit.
>> >> >>
>> >> >> Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
>> >> >> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
>> >> >> ---
>> >> >> Changes in v1 -> v2:
>> >> >> * Define attribute_used_retain_section
>> >> >> Changes in v2 -> v3:
>> >> >> * Use attribute_used_retain instead attribute_used_retain_section
>> >> >> Changes in v3 -> v4:
>> >> >> * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
>> >> >> Changes in v4 -> v5:
>> >> >> * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
>> >> >> * Rename *gcc_retain* to *gnu_retain*
>> >> >> ---
>> >> >>  config.h.in            |  3 +++
>> >> >>  configure              | 59 ++++++++++++++++++++++++++++++++++++++++++
>> >> >>  configure.ac           | 21 +++++++++++++++
>> >> >>  include/libc-symbols.h | 14 +++++++---
>> >> >>  libio/Makefile         | 32 +++++++++++++++++++++++
>> >> >>  libio/tst-cleanup.c    | 33 +++++++++++++++++++++++
>> >> >>  libio/tst-cleanup.exp  |  1 +
>> >> >>  7 files changed, 159 insertions(+), 4 deletions(-)
>> >> >>  create mode 100644 libio/tst-cleanup.c
>> >> >>  create mode 100644 libio/tst-cleanup.exp
>> >> >>
>> >> >> diff --git a/config.h.in b/config.h.in
>> >> >> index ca1547ae67..96a08c7757 100644
>> >> >> --- a/config.h.in
>> >> >> +++ b/config.h.in
>> >> >> @@ -187,6 +187,9 @@
>> >> >>  /* Define if gcc supports attribute ifunc.  */
>> >> >>  #undef HAVE_GCC_IFUNC
>> >> >>
>> >> >> +/* Define if CC supports attribute retain.  */
>> >> >> +#undef HAVE_GNU_RETAIN
>> >> >> +
>> >> >>  /* Define if the linker defines __ehdr_start.  */
>> >> >>  #undef HAVE_EHDR_START
>> >> >>
>> >> >> diff --git a/configure b/configure
>> >> >> index fcf43bf7de..e64b7f8efe 100755
>> >> >> --- a/configure
>> >> >> +++ b/configure
>> >> >> @@ -4105,6 +4105,31 @@ fi
>> >> >>  $as_echo "$libc_cv_textrel_ifunc" >&6; }
>> >> >>
>> >> >>
>> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
>> >> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
>> >> >> +if ${libc_cv_gnu_retain+:} false; then :
>> >> >> +  $as_echo_n "(cached) " >&6
>> >> >> +else
>> >> >> +  cat > conftest.c <<EOF
>> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> >> +EOF
>> >> >> +libc_cv_gnu_retain=no
>> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
>> >> >> +   2>&5 ; then
>> >> >> +  libc_cv_gnu_retain=yes
>> >> >> +fi
>> >> >> +rm -f conftest*
>> >> >> +fi
>> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
>> >> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
>> >> >> +if test $libc_cv_gnu_retain = yes; then
>> >> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
>> >> >> +
>> >> >> +fi
>> >> >> +config_vars="$config_vars
>> >> >> +have-gnu-retain = $libc_cv_gnu_retain"
>> >> >> +
>> >> >>  # Check if gcc warns about alias for function with incompatible types.
>> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
>> >> >>  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
>> >> >> @@ -5871,6 +5896,40 @@ fi
>> >> >>  $as_echo "$libc_linker_feature" >&6; }
>> >> >>
>> >> >>
>> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
>> >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
>> >> >> +libc_linker_feature=no
>> >> >> +if test x"$gnu_ld" = x"yes"; then
>> >> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
>> >> >> +  if test -n "$libc_linker_check"; then
>> >> >> +    cat > conftest.c <<EOF
>> >> >> +int _start (void) { return 42; }
>> >> >> +EOF
>> >> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
>> >> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
>> >> >> +                               -fPIC -shared -o conftest.so conftest.c
>> >> >> +                               1>&5'
>> >> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
>> >> >> +  (eval $ac_try) 2>&5
>> >> >> +  ac_status=$?
>> >> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
>> >> >> +  test $ac_status = 0; }; }
>> >> >> +    then
>> >> >> +      libc_linker_feature=yes
>> >> >> +    fi
>> >> >> +    rm -f conftest*
>> >> >> +  fi
>> >> >> +fi
>> >> >> +if test $libc_linker_feature = yes; then
>> >> >> +  libc_cv_z_start_stop_gc=yes
>> >> >> +else
>> >> >> +  libc_cv_z_start_stop_gc=no
>> >> >> +fi
>> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
>> >> >> +$as_echo "$libc_linker_feature" >&6; }
>> >> >> +config_vars="$config_vars
>> >> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
>> >> >> +
>> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>> >> >>  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>> >> >>  libc_linker_feature=no
>> >> >> diff --git a/configure.ac b/configure.ac
>> >> >> index fce967f2c2..cc47e56e82 100644
>> >> >> --- a/configure.ac
>> >> >> +++ b/configure.ac
>> >> >> @@ -707,6 +707,23 @@ fi
>> >> >>  rm -f conftest*])
>> >> >>  AC_SUBST(libc_cv_textrel_ifunc)
>> >> >>
>> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> >> +AC_CACHE_CHECK([for GNU attribute retain support],
>> >> >> +              libc_cv_gnu_retain, [dnl
>> >> >> +cat > conftest.c <<EOF
>> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> >> +EOF
>> >> >> +libc_cv_gnu_retain=no
>> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
>> >> >> +   2>&AS_MESSAGE_LOG_FD ; then
>> >> >> +  libc_cv_gnu_retain=yes
>> >> >> +fi
>> >> >> +rm -f conftest*])
>> >> >> +if test $libc_cv_gnu_retain = yes; then
>> >> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
>> >> >> +fi
>> >> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
>> >> >> +
>> >> >>  # Check if gcc warns about alias for function with incompatible types.
>> >> >>  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>> >> >>                libc_cv_gcc_incompatible_alias, [dnl
>> >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>> >> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>> >> >>  AC_SUBST(libc_cv_z_execstack)
>> >> >>
>> >> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
>> >> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
>> >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
>> >> >> +
>> >> >>  LIBC_LINKER_FEATURE([--no-dynamic-linker],
>> >> >>                     [-Wl,--no-dynamic-linker],
>> >> >>                     [libc_cv_no_dynamic_linker=yes],
>> >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
>> >> >> index 546fc26a7b..127ea656c2 100644
>> >> >> --- a/include/libc-symbols.h
>> >> >> +++ b/include/libc-symbols.h
>> >> >> @@ -352,6 +352,12 @@ for linking")
>> >> >>
>> >> >>  */
>> >> >>
>> >> >> +#ifdef HAVE_GNU_RETAIN
>> >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
>> >> >> +#else
>> >> >> +# define attribute_used_retain __attribute__ ((__used__))
>> >> >> +#endif
>> >> >> +
>> >> >>  /* Symbol set support macros.  */
>> >> >>
>> >> >>  /* Make SYMBOL, which is in the text segment, an element of SET.  */
>> >> >> @@ -367,12 +373,12 @@ for linking")
>> >> >>  /* When building a shared library, make the set section writable,
>> >> >>     because it will need to be relocated at run time anyway.  */
>> >> >>  # define _elf_set_element(set, symbol) \
>> >> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
>> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
>> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >> >>  #else
>> >> >>  # define _elf_set_element(set, symbol) \
>> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >> >>  #endif
>> >> >>
>> >> >>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
>> >> >> diff --git a/libio/Makefile b/libio/Makefile
>> >> >> index 12ce41038f..c9c232ebc2 100644
>> >> >> --- a/libio/Makefile
>> >> >> +++ b/libio/Makefile
>> >> >> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared))
>> >> >>  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>> >> >>                  $(objpfx)tst-bz24228-mem.out
>> >> >>  endif
>> >> >> +
>> >> >> +tests += tst-cleanup-default
>> >> >> +tests-static += tst-cleanup-default
>> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out
>> >> >
>> >> >Please make 2 tests,  tst-cleanup-default and tst-cleanup-default-static.
>> >>
>> >> Added.
>> >>
>> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> >> >> +
>> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
>> >> >> +tests-static += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
>> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
>> >> >
>> >> >Same here.
>> >>
>> >> Added.
>> >>
>> >> >> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
>> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc
>> >> >> +endif
>> >> >>  endif
>> >> >>
>> >> >>  include ../Rules
>> >> >> @@ -224,6 +238,24 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>> >> >>  $(objpfx)tst-wfile-sync.out: $(gen-locales)
>> >> >>  endif
>> >> >>
>> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> >> >> +       cmp $^ > $@; \
>> >> >> +       $(evaluate-test)
>> >> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
>> >> >> +       $(compile.c) -o $@
>> >> >> +
>> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> >> >> +       cmp $^ > $@; \
>> >> >> +       $(evaluate-test)
>> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> >> >> +       $(compile.c) -o $@
>> >> >> +
>> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
>> >> >> +       cmp $^ > $@; \
>> >> >> +       $(evaluate-test)
>> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
>> >> >> +       $(compile.c) -o $@
>> >> >>
>> >> >>  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>> >> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>> >> >>         $(common-objpfx)libio/; \
>> >> >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
>> >> >> new file mode 100644
>> >> >> index 0000000000..7f0a34a91e
>> >> >> --- /dev/null
>> >> >> +++ b/libio/tst-cleanup.c
>> >> >> @@ -0,0 +1,33 @@
>> >> >
>> >> >Please add a comment saying that test --gc-sections.
>> >>
>> >> OK, added.
>> >>
>> >> >> +/* Copyright (C) 2021 Free Software Foundation, Inc.
>> >> >> +   This file is part of the GNU C Library.
>> >> >> +
>> >> >> +   The GNU C Library is free software; you can redistribute it and/or
>> >> >> +   modify it under the terms of the GNU Lesser General Public
>> >> >> +   License as published by the Free Software Foundation; either
>> >> >> +   version 2.1 of the License, or (at your option) any later version.
>> >> >> +
>> >> >> +   The GNU C Library is distributed in the hope that it will be useful,
>> >> >> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>> >> >> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> >> >> +   Lesser General Public License for more details.
>> >> >> +
>> >> >> +   You should have received a copy of the GNU Lesser General Public
>> >> >> +   License along with the GNU C Library; if not, see
>> >> >> +   <https://www.gnu.org/licenses/>.  */
>> >> >> +
>> >> >> +/* Test that stdout is flushed after atexit callbacks were run.  */
>> >> >> +
>> >> >> +#include <stdio.h>
>> >> >> +#include <stdlib.h>
>> >> >> +
>> >> >> +void
>> >> >> +hook (void)
>> >> >> +{
>> >> >> +  puts ("hello");
>> >> >> +}
>> >> >> +
>> >> >> +int
>> >> >> +main (void)
>> >> >> +{
>> >> >> +  atexit (hook);
>> >> >> +}
>> >> >> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
>> >> >> new file mode 100644
>> >> >> index 0000000000..ce01362503
>> >> >> --- /dev/null
>> >> >> +++ b/libio/tst-cleanup.exp
>> >> >> @@ -0,0 +1 @@
>> >> >> +hello
>> >> >> --
>> >> >> 2.31.0.291.g576ba9dcdaf-goog
>> >> >>
>> >> >
>> >>
>> >> diff --git a/config.h.in b/config.h.in
>> >> index ca1547ae67..96a08c7757 100644
>> >> --- a/config.h.in
>> >> +++ b/config.h.in
>> >> @@ -187,6 +187,9 @@
>> >>   /* Define if gcc supports attribute ifunc.  */
>> >>   #undef HAVE_GCC_IFUNC
>> >>
>> >> +/* Define if CC supports attribute retain.  */
>> >> +#undef HAVE_GNU_RETAIN
>> >> +
>> >>   /* Define if the linker defines __ehdr_start.  */
>> >>   #undef HAVE_EHDR_START
>> >>
>> >> diff --git a/configure b/configure
>> >> index fcf43bf7de..e64b7f8efe 100755
>> >> --- a/configure
>> >> +++ b/configure
>> >> @@ -4105,6 +4105,31 @@ fi
>> >>   $as_echo "$libc_cv_textrel_ifunc" >&6; }
>> >>
>> >>
>> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
>> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
>> >> +if ${libc_cv_gnu_retain+:} false; then :
>> >> +  $as_echo_n "(cached) " >&6
>> >> +else
>> >> +  cat > conftest.c <<EOF
>> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> +EOF
>> >> +libc_cv_gnu_retain=no
>> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
>> >> +   2>&5 ; then
>> >> +  libc_cv_gnu_retain=yes
>> >> +fi
>> >> +rm -f conftest*
>> >> +fi
>> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
>> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
>> >> +if test $libc_cv_gnu_retain = yes; then
>> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
>> >> +
>> >> +fi
>> >> +config_vars="$config_vars
>> >> +have-gnu-retain = $libc_cv_gnu_retain"
>> >> +
>> >>   # Check if gcc warns about alias for function with incompatible types.
>> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
>> >>   $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
>> >> @@ -5871,6 +5896,40 @@ fi
>> >>   $as_echo "$libc_linker_feature" >&6; }
>> >>
>> >>
>> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
>> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
>> >> +libc_linker_feature=no
>> >> +if test x"$gnu_ld" = x"yes"; then
>> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
>> >> +  if test -n "$libc_linker_check"; then
>> >> +    cat > conftest.c <<EOF
>> >> +int _start (void) { return 42; }
>> >> +EOF
>> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
>> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
>> >> +                               -fPIC -shared -o conftest.so conftest.c
>> >> +                               1>&5'
>> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
>> >> +  (eval $ac_try) 2>&5
>> >> +  ac_status=$?
>> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
>> >> +  test $ac_status = 0; }; }
>> >> +    then
>> >> +      libc_linker_feature=yes
>> >> +    fi
>> >> +    rm -f conftest*
>> >> +  fi
>> >> +fi
>> >> +if test $libc_linker_feature = yes; then
>> >> +  libc_cv_z_start_stop_gc=yes
>> >> +else
>> >> +  libc_cv_z_start_stop_gc=no
>> >> +fi
>> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
>> >> +$as_echo "$libc_linker_feature" >&6; }
>> >> +config_vars="$config_vars
>> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
>> >> +
>> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>> >>   $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>> >>   libc_linker_feature=no
>> >> diff --git a/configure.ac b/configure.ac
>> >> index fce967f2c2..cc47e56e82 100644
>> >> --- a/configure.ac
>> >> +++ b/configure.ac
>> >> @@ -707,6 +707,23 @@ fi
>> >>   rm -f conftest*])
>> >>   AC_SUBST(libc_cv_textrel_ifunc)
>> >>
>> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> +AC_CACHE_CHECK([for GNU attribute retain support],
>> >> +              libc_cv_gnu_retain, [dnl
>> >> +cat > conftest.c <<EOF
>> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> +EOF
>> >> +libc_cv_gnu_retain=no
>> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
>> >> +   2>&AS_MESSAGE_LOG_FD ; then
>> >> +  libc_cv_gnu_retain=yes
>> >> +fi
>> >> +rm -f conftest*])
>> >> +if test $libc_cv_gnu_retain = yes; then
>> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
>> >> +fi
>> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
>> >> +
>> >>   # Check if gcc warns about alias for function with incompatible types.
>> >>   AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>> >>                libc_cv_gcc_incompatible_alias, [dnl
>> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>> >>   AC_SUBST(libc_cv_z_execstack)
>> >>
>> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
>> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
>> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
>> >> +
>> >>   LIBC_LINKER_FEATURE([--no-dynamic-linker],
>> >>                     [-Wl,--no-dynamic-linker],
>> >>                     [libc_cv_no_dynamic_linker=yes],
>> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
>> >> index 546fc26a7b..127ea656c2 100644
>> >> --- a/include/libc-symbols.h
>> >> +++ b/include/libc-symbols.h
>> >> @@ -352,6 +352,12 @@ for linking")
>> >>
>> >>   */
>> >>
>> >> +#ifdef HAVE_GNU_RETAIN
>> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
>> >> +#else
>> >> +# define attribute_used_retain __attribute__ ((__used__))
>> >> +#endif
>> >> +
>> >>   /* Symbol set support macros.  */
>> >>
>> >>   /* Make SYMBOL, which is in the text segment, an element of SET.  */
>> >> @@ -367,12 +373,12 @@ for linking")
>> >>   /* When building a shared library, make the set section writable,
>> >>      because it will need to be relocated at run time anyway.  */
>> >>   # define _elf_set_element(set, symbol) \
>> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
>> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
>> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >>   #else
>> >>   # define _elf_set_element(set, symbol) \
>> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >>   #endif
>> >>
>> >>   /* Define SET as a symbol set.  This may be required (it is in a.out) to
>> >> diff --git a/libio/Makefile b/libio/Makefile
>> >> index 12ce41038f..ad0d53bb49 100644
>> >> --- a/libio/Makefile
>> >> +++ b/libio/Makefile
>> >> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
>> >>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>> >>                  $(objpfx)tst-bz24228-mem.out
>> >>   endif
>> >> +
>> >> +tests += tst-cleanup-default tst-cleanup-default-static
>> >> +tests-static += tst-cleanup-default-static
>> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
>> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> >> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
>> >> +
>> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
>> >> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
>> >> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
>> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> >> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
>> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
>> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
>> >> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
>> >> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
>> >> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
>> >> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
>> >> +endif
>> >>   endif
>> >>
>> >>   include ../Rules
>> >> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>> >>   endif
>> >>
>> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
>> >> +       $(compile.c) -o $@
>> >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-default-static.o: tst-cleanup.c
>> >> +       $(compile.c) -o $@
>> >> +
>> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> >> +       $(compile.c) -o $@
>> >> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c
>> >> +       $(compile.c) -o $@
>> >
>> >Please add a separate .c file for each test to get the correct dependency.
>>
>> Changed this block to:
>>
>> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>>   endif
>>
>> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-default.c: tst-cleanup.c
>> +       cp $< $@
>> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-default-static.c: tst-cleanup.c
>> +       cp $< $@
>> +
>> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> +       $(compile.c) -o $@
>> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-start-stop-gc-static.c: tst-cleanup.c
>> +       cp $< $@
>> +
>> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-nostart-stop-gc.c: tst-cleanup.c
>> +       cp $< $@
>> +$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc-static.out
>> +       cmp $^ > $@; \
>> +       $(evaluate-test)
>> +$(objpfx)tst-cleanup-nostart-stop-gc-static.c: tst-cleanup.c
>> +       cp $< $@
>> +
>>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>>         $(common-objpfx)libio/; \
>>
>
>"make clean" doesn't remove the generated files. The standard way in glibc
>is to add a *-static.c source.

I'll use .INTERMEDIATE and $(eval $(call ..))

diff --git a/libio/Makefile b/libio/Makefile
index 12ce41038f..a9b44f04df 100644
--- a/libio/Makefile
+++ b/libio/Makefile
@@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
  		 $(objpfx)tst-bz24228-mem.out
  endif
+
+tests += tst-cleanup-default tst-cleanup-default-static
+tests-static += tst-cleanup-default-static
+tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
+LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
+LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
+
+ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
+tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
+		tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
+tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
+tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
+		$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
+		$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
+		$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
+LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
+LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
+LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
+LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
+endif
  endif
  
  include ../Rules
@@ -224,6 +244,17 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
  $(objpfx)tst-wfile-sync.out: $(gen-locales)
  endif
  
+define gen-tst-cleanup
+$(objpfx)tst-cleanup-$1-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-$1.out
+	cmp $$^ > $$@; $$(evaluate-test)
+$(objpfx)tst-cleanup-$1.c: tst-cleanup.c
+	cp $$< $$@
+.INTERMEDIATE: $(objpfx)tst-cleanup-$1.c
+endef
+
+$(foreach t, default default-static start-stop-gc start-stop-gc-static nostart-stop-gc nostart-stop-gc-static, \
+  $(eval $(call gen-tst-cleanup,$(t))))
+
  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
  	$(SHELL) $< $(common-objpfx) '$(test-program-prefix)'	\
  	$(common-objpfx)libio/; \
  

On Sat, Apr 3, 2021 at 2:57 PM Fangrui Song <maskray@google.com> wrote:
>
> On 2021-04-03, H.J. Lu wrote:
> >On Sat, Apr 3, 2021 at 11:02 AM Fangrui Song <maskray@google.com> wrote:
> >>
> >>
> >> On 2021-04-02, H.J. Lu wrote:
> >> >On Thu, Apr 1, 2021 at 8:23 PM Fangrui Song <maskray@google.com> wrote:
> >> >>
> >> >> On 2021-04-01, H.J. Lu wrote:
> >> >> >On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song <maskray@google.com> wrote:
> >> >> >>
> >> >> >> So that text_set_element/data_set_element/bss_set_element defined
> >> >> >> variables will be retained by the linker.
> >> >> >>
> >> >> >> Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
> >> >> >> will not be optimized out; 'retain' prevents section garbage collection
> >> >> >> if the linker support SHF_GNU_RETAIN.
> >> >> >>
> >> >> >> GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
> >> >> >> identifier name sections to be GCed even if there are live
> >> >> >> __start_/__stop_ references.
> >> >> >>
> >> >> >> Without the change, there are some static linking problems, e.g.
> >> >> >> _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
> >> >> >> stdout is not flushed on exit.
> >> >> >>
> >> >> >> Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
> >> >> >> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
> >> >> >> ---
> >> >> >> Changes in v1 -> v2:
> >> >> >> * Define attribute_used_retain_section
> >> >> >> Changes in v2 -> v3:
> >> >> >> * Use attribute_used_retain instead attribute_used_retain_section
> >> >> >> Changes in v3 -> v4:
> >> >> >> * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
> >> >> >> Changes in v4 -> v5:
> >> >> >> * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
> >> >> >> * Rename *gcc_retain* to *gnu_retain*
> >> >> >> ---
> >> >> >>  config.h.in            |  3 +++
> >> >> >>  configure              | 59 ++++++++++++++++++++++++++++++++++++++++++
> >> >> >>  configure.ac           | 21 +++++++++++++++
> >> >> >>  include/libc-symbols.h | 14 +++++++---
> >> >> >>  libio/Makefile         | 32 +++++++++++++++++++++++
> >> >> >>  libio/tst-cleanup.c    | 33 +++++++++++++++++++++++
> >> >> >>  libio/tst-cleanup.exp  |  1 +
> >> >> >>  7 files changed, 159 insertions(+), 4 deletions(-)
> >> >> >>  create mode 100644 libio/tst-cleanup.c
> >> >> >>  create mode 100644 libio/tst-cleanup.exp
> >> >> >>
> >> >> >> diff --git a/config.h.in b/config.h.in
> >> >> >> index ca1547ae67..96a08c7757 100644
> >> >> >> --- a/config.h.in
> >> >> >> +++ b/config.h.in
> >> >> >> @@ -187,6 +187,9 @@
> >> >> >>  /* Define if gcc supports attribute ifunc.  */
> >> >> >>  #undef HAVE_GCC_IFUNC
> >> >> >>
> >> >> >> +/* Define if CC supports attribute retain.  */
> >> >> >> +#undef HAVE_GNU_RETAIN
> >> >> >> +
> >> >> >>  /* Define if the linker defines __ehdr_start.  */
> >> >> >>  #undef HAVE_EHDR_START
> >> >> >>
> >> >> >> diff --git a/configure b/configure
> >> >> >> index fcf43bf7de..e64b7f8efe 100755
> >> >> >> --- a/configure
> >> >> >> +++ b/configure
> >> >> >> @@ -4105,6 +4105,31 @@ fi
> >> >> >>  $as_echo "$libc_cv_textrel_ifunc" >&6; }
> >> >> >>
> >> >> >>
> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
> >> >> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
> >> >> >> +if ${libc_cv_gnu_retain+:} false; then :
> >> >> >> +  $as_echo_n "(cached) " >&6
> >> >> >> +else
> >> >> >> +  cat > conftest.c <<EOF
> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> >> +EOF
> >> >> >> +libc_cv_gnu_retain=no
> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> >> >> >> +   2>&5 ; then
> >> >> >> +  libc_cv_gnu_retain=yes
> >> >> >> +fi
> >> >> >> +rm -f conftest*
> >> >> >> +fi
> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
> >> >> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
> >> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
> >> >> >> +
> >> >> >> +fi
> >> >> >> +config_vars="$config_vars
> >> >> >> +have-gnu-retain = $libc_cv_gnu_retain"
> >> >> >> +
> >> >> >>  # Check if gcc warns about alias for function with incompatible types.
> >> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
> >> >> >>  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
> >> >> >> @@ -5871,6 +5896,40 @@ fi
> >> >> >>  $as_echo "$libc_linker_feature" >&6; }
> >> >> >>
> >> >> >>
> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
> >> >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
> >> >> >> +libc_linker_feature=no
> >> >> >> +if test x"$gnu_ld" = x"yes"; then
> >> >> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
> >> >> >> +  if test -n "$libc_linker_check"; then
> >> >> >> +    cat > conftest.c <<EOF
> >> >> >> +int _start (void) { return 42; }
> >> >> >> +EOF
> >> >> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> >> >> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
> >> >> >> +                               -fPIC -shared -o conftest.so conftest.c
> >> >> >> +                               1>&5'
> >> >> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> >> >> >> +  (eval $ac_try) 2>&5
> >> >> >> +  ac_status=$?
> >> >> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> >> >> >> +  test $ac_status = 0; }; }
> >> >> >> +    then
> >> >> >> +      libc_linker_feature=yes
> >> >> >> +    fi
> >> >> >> +    rm -f conftest*
> >> >> >> +  fi
> >> >> >> +fi
> >> >> >> +if test $libc_linker_feature = yes; then
> >> >> >> +  libc_cv_z_start_stop_gc=yes
> >> >> >> +else
> >> >> >> +  libc_cv_z_start_stop_gc=no
> >> >> >> +fi
> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> >> >> >> +$as_echo "$libc_linker_feature" >&6; }
> >> >> >> +config_vars="$config_vars
> >> >> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
> >> >> >> +
> >> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
> >> >> >>  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
> >> >> >>  libc_linker_feature=no
> >> >> >> diff --git a/configure.ac b/configure.ac
> >> >> >> index fce967f2c2..cc47e56e82 100644
> >> >> >> --- a/configure.ac
> >> >> >> +++ b/configure.ac
> >> >> >> @@ -707,6 +707,23 @@ fi
> >> >> >>  rm -f conftest*])
> >> >> >>  AC_SUBST(libc_cv_textrel_ifunc)
> >> >> >>
> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> >> +AC_CACHE_CHECK([for GNU attribute retain support],
> >> >> >> +              libc_cv_gnu_retain, [dnl
> >> >> >> +cat > conftest.c <<EOF
> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> >> +EOF
> >> >> >> +libc_cv_gnu_retain=no
> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
> >> >> >> +   2>&AS_MESSAGE_LOG_FD ; then
> >> >> >> +  libc_cv_gnu_retain=yes
> >> >> >> +fi
> >> >> >> +rm -f conftest*])
> >> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
> >> >> >> +fi
> >> >> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
> >> >> >> +
> >> >> >>  # Check if gcc warns about alias for function with incompatible types.
> >> >> >>  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
> >> >> >>                libc_cv_gcc_incompatible_alias, [dnl
> >> >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
> >> >> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
> >> >> >>  AC_SUBST(libc_cv_z_execstack)
> >> >> >>
> >> >> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> >> >> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> >> >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
> >> >> >> +
> >> >> >>  LIBC_LINKER_FEATURE([--no-dynamic-linker],
> >> >> >>                     [-Wl,--no-dynamic-linker],
> >> >> >>                     [libc_cv_no_dynamic_linker=yes],
> >> >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
> >> >> >> index 546fc26a7b..127ea656c2 100644
> >> >> >> --- a/include/libc-symbols.h
> >> >> >> +++ b/include/libc-symbols.h
> >> >> >> @@ -352,6 +352,12 @@ for linking")
> >> >> >>
> >> >> >>  */
> >> >> >>
> >> >> >> +#ifdef HAVE_GNU_RETAIN
> >> >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
> >> >> >> +#else
> >> >> >> +# define attribute_used_retain __attribute__ ((__used__))
> >> >> >> +#endif
> >> >> >> +
> >> >> >>  /* Symbol set support macros.  */
> >> >> >>
> >> >> >>  /* Make SYMBOL, which is in the text segment, an element of SET.  */
> >> >> >> @@ -367,12 +373,12 @@ for linking")
> >> >> >>  /* When building a shared library, make the set section writable,
> >> >> >>     because it will need to be relocated at run time anyway.  */
> >> >> >>  # define _elf_set_element(set, symbol) \
> >> >> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >> >>  #else
> >> >> >>  # define _elf_set_element(set, symbol) \
> >> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >> >>  #endif
> >> >> >>
> >> >> >>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
> >> >> >> diff --git a/libio/Makefile b/libio/Makefile
> >> >> >> index 12ce41038f..c9c232ebc2 100644
> >> >> >> --- a/libio/Makefile
> >> >> >> +++ b/libio/Makefile
> >> >> >> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared))
> >> >> >>  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
> >> >> >>                  $(objpfx)tst-bz24228-mem.out
> >> >> >>  endif
> >> >> >> +
> >> >> >> +tests += tst-cleanup-default
> >> >> >> +tests-static += tst-cleanup-default
> >> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out
> >> >> >
> >> >> >Please make 2 tests,  tst-cleanup-default and tst-cleanup-default-static.
> >> >>
> >> >> Added.
> >> >>
> >> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> >> >> >> +
> >> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> >> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> >> >> >> +tests-static += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> >> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> >> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
> >> >> >
> >> >> >Same here.
> >> >>
> >> >> Added.
> >> >>
> >> >> >> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
> >> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc
> >> >> >> +endif
> >> >> >>  endif
> >> >> >>
> >> >> >>  include ../Rules
> >> >> >> @@ -224,6 +238,24 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >> >> >>  $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >> >> >>  endif
> >> >> >>
> >> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> >> >> >> +       cmp $^ > $@; \
> >> >> >> +       $(evaluate-test)
> >> >> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
> >> >> >> +       $(compile.c) -o $@
> >> >> >> +
> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> >> >> >> +       cmp $^ > $@; \
> >> >> >> +       $(evaluate-test)
> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> >> >> >> +       $(compile.c) -o $@
> >> >> >> +
> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
> >> >> >> +       cmp $^ > $@; \
> >> >> >> +       $(evaluate-test)
> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
> >> >> >> +       $(compile.c) -o $@
> >> >> >>
> >> >> >>  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
> >> >> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
> >> >> >>         $(common-objpfx)libio/; \
> >> >> >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
> >> >> >> new file mode 100644
> >> >> >> index 0000000000..7f0a34a91e
> >> >> >> --- /dev/null
> >> >> >> +++ b/libio/tst-cleanup.c
> >> >> >> @@ -0,0 +1,33 @@
> >> >> >
> >> >> >Please add a comment saying that test --gc-sections.
> >> >>
> >> >> OK, added.
> >> >>
> >> >> >> +/* Copyright (C) 2021 Free Software Foundation, Inc.
> >> >> >> +   This file is part of the GNU C Library.
> >> >> >> +
> >> >> >> +   The GNU C Library is free software; you can redistribute it and/or
> >> >> >> +   modify it under the terms of the GNU Lesser General Public
> >> >> >> +   License as published by the Free Software Foundation; either
> >> >> >> +   version 2.1 of the License, or (at your option) any later version.
> >> >> >> +
> >> >> >> +   The GNU C Library is distributed in the hope that it will be useful,
> >> >> >> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> >> >> >> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> >> >> >> +   Lesser General Public License for more details.
> >> >> >> +
> >> >> >> +   You should have received a copy of the GNU Lesser General Public
> >> >> >> +   License along with the GNU C Library; if not, see
> >> >> >> +   <https://www.gnu.org/licenses/>.  */
> >> >> >> +
> >> >> >> +/* Test that stdout is flushed after atexit callbacks were run.  */
> >> >> >> +
> >> >> >> +#include <stdio.h>
> >> >> >> +#include <stdlib.h>
> >> >> >> +
> >> >> >> +void
> >> >> >> +hook (void)
> >> >> >> +{
> >> >> >> +  puts ("hello");
> >> >> >> +}
> >> >> >> +
> >> >> >> +int
> >> >> >> +main (void)
> >> >> >> +{
> >> >> >> +  atexit (hook);
> >> >> >> +}
> >> >> >> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
> >> >> >> new file mode 100644
> >> >> >> index 0000000000..ce01362503
> >> >> >> --- /dev/null
> >> >> >> +++ b/libio/tst-cleanup.exp
> >> >> >> @@ -0,0 +1 @@
> >> >> >> +hello
> >> >> >> --
> >> >> >> 2.31.0.291.g576ba9dcdaf-goog
> >> >> >>
> >> >> >
> >> >>
> >> >> diff --git a/config.h.in b/config.h.in
> >> >> index ca1547ae67..96a08c7757 100644
> >> >> --- a/config.h.in
> >> >> +++ b/config.h.in
> >> >> @@ -187,6 +187,9 @@
> >> >>   /* Define if gcc supports attribute ifunc.  */
> >> >>   #undef HAVE_GCC_IFUNC
> >> >>
> >> >> +/* Define if CC supports attribute retain.  */
> >> >> +#undef HAVE_GNU_RETAIN
> >> >> +
> >> >>   /* Define if the linker defines __ehdr_start.  */
> >> >>   #undef HAVE_EHDR_START
> >> >>
> >> >> diff --git a/configure b/configure
> >> >> index fcf43bf7de..e64b7f8efe 100755
> >> >> --- a/configure
> >> >> +++ b/configure
> >> >> @@ -4105,6 +4105,31 @@ fi
> >> >>   $as_echo "$libc_cv_textrel_ifunc" >&6; }
> >> >>
> >> >>
> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
> >> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
> >> >> +if ${libc_cv_gnu_retain+:} false; then :
> >> >> +  $as_echo_n "(cached) " >&6
> >> >> +else
> >> >> +  cat > conftest.c <<EOF
> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> +EOF
> >> >> +libc_cv_gnu_retain=no
> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> >> >> +   2>&5 ; then
> >> >> +  libc_cv_gnu_retain=yes
> >> >> +fi
> >> >> +rm -f conftest*
> >> >> +fi
> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
> >> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
> >> >> +
> >> >> +fi
> >> >> +config_vars="$config_vars
> >> >> +have-gnu-retain = $libc_cv_gnu_retain"
> >> >> +
> >> >>   # Check if gcc warns about alias for function with incompatible types.
> >> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
> >> >>   $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
> >> >> @@ -5871,6 +5896,40 @@ fi
> >> >>   $as_echo "$libc_linker_feature" >&6; }
> >> >>
> >> >>
> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
> >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
> >> >> +libc_linker_feature=no
> >> >> +if test x"$gnu_ld" = x"yes"; then
> >> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
> >> >> +  if test -n "$libc_linker_check"; then
> >> >> +    cat > conftest.c <<EOF
> >> >> +int _start (void) { return 42; }
> >> >> +EOF
> >> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> >> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
> >> >> +                               -fPIC -shared -o conftest.so conftest.c
> >> >> +                               1>&5'
> >> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> >> >> +  (eval $ac_try) 2>&5
> >> >> +  ac_status=$?
> >> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> >> >> +  test $ac_status = 0; }; }
> >> >> +    then
> >> >> +      libc_linker_feature=yes
> >> >> +    fi
> >> >> +    rm -f conftest*
> >> >> +  fi
> >> >> +fi
> >> >> +if test $libc_linker_feature = yes; then
> >> >> +  libc_cv_z_start_stop_gc=yes
> >> >> +else
> >> >> +  libc_cv_z_start_stop_gc=no
> >> >> +fi
> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> >> >> +$as_echo "$libc_linker_feature" >&6; }
> >> >> +config_vars="$config_vars
> >> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
> >> >> +
> >> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
> >> >>   $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
> >> >>   libc_linker_feature=no
> >> >> diff --git a/configure.ac b/configure.ac
> >> >> index fce967f2c2..cc47e56e82 100644
> >> >> --- a/configure.ac
> >> >> +++ b/configure.ac
> >> >> @@ -707,6 +707,23 @@ fi
> >> >>   rm -f conftest*])
> >> >>   AC_SUBST(libc_cv_textrel_ifunc)
> >> >>
> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> +AC_CACHE_CHECK([for GNU attribute retain support],
> >> >> +              libc_cv_gnu_retain, [dnl
> >> >> +cat > conftest.c <<EOF
> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> +EOF
> >> >> +libc_cv_gnu_retain=no
> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
> >> >> +   2>&AS_MESSAGE_LOG_FD ; then
> >> >> +  libc_cv_gnu_retain=yes
> >> >> +fi
> >> >> +rm -f conftest*])
> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
> >> >> +fi
> >> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
> >> >> +
> >> >>   # Check if gcc warns about alias for function with incompatible types.
> >> >>   AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
> >> >>                libc_cv_gcc_incompatible_alias, [dnl
> >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
> >> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
> >> >>   AC_SUBST(libc_cv_z_execstack)
> >> >>
> >> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> >> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
> >> >> +
> >> >>   LIBC_LINKER_FEATURE([--no-dynamic-linker],
> >> >>                     [-Wl,--no-dynamic-linker],
> >> >>                     [libc_cv_no_dynamic_linker=yes],
> >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
> >> >> index 546fc26a7b..127ea656c2 100644
> >> >> --- a/include/libc-symbols.h
> >> >> +++ b/include/libc-symbols.h
> >> >> @@ -352,6 +352,12 @@ for linking")
> >> >>
> >> >>   */
> >> >>
> >> >> +#ifdef HAVE_GNU_RETAIN
> >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
> >> >> +#else
> >> >> +# define attribute_used_retain __attribute__ ((__used__))
> >> >> +#endif
> >> >> +
> >> >>   /* Symbol set support macros.  */
> >> >>
> >> >>   /* Make SYMBOL, which is in the text segment, an element of SET.  */
> >> >> @@ -367,12 +373,12 @@ for linking")
> >> >>   /* When building a shared library, make the set section writable,
> >> >>      because it will need to be relocated at run time anyway.  */
> >> >>   # define _elf_set_element(set, symbol) \
> >> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >>   #else
> >> >>   # define _elf_set_element(set, symbol) \
> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >>   #endif
> >> >>
> >> >>   /* Define SET as a symbol set.  This may be required (it is in a.out) to
> >> >> diff --git a/libio/Makefile b/libio/Makefile
> >> >> index 12ce41038f..ad0d53bb49 100644
> >> >> --- a/libio/Makefile
> >> >> +++ b/libio/Makefile
> >> >> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
> >> >>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
> >> >>                  $(objpfx)tst-bz24228-mem.out
> >> >>   endif
> >> >> +
> >> >> +tests += tst-cleanup-default tst-cleanup-default-static
> >> >> +tests-static += tst-cleanup-default-static
> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> >> >> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
> >> >> +
> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
> >> >> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
> >> >> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> >> >> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
> >> >> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
> >> >> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
> >> >> +endif
> >> >>   endif
> >> >>
> >> >>   include ../Rules
> >> >> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >> >>   endif
> >> >>
> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
> >> >> +       $(compile.c) -o $@
> >> >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-default-static.o: tst-cleanup.c
> >> >> +       $(compile.c) -o $@
> >> >> +
> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> >> >> +       $(compile.c) -o $@
> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c
> >> >> +       $(compile.c) -o $@
> >> >
> >> >Please add a separate .c file for each test to get the correct dependency.
> >>
> >> Changed this block to:
> >>
> >> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >>   endif
> >>
> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-default.c: tst-cleanup.c
> >> +       cp $< $@
> >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-default-static.c: tst-cleanup.c
> >> +       cp $< $@
> >> +
> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> >> +       $(compile.c) -o $@
> >> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-start-stop-gc-static.c: tst-cleanup.c
> >> +       cp $< $@
> >> +
> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-nostart-stop-gc.c: tst-cleanup.c
> >> +       cp $< $@
> >> +$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc-static.out
> >> +       cmp $^ > $@; \
> >> +       $(evaluate-test)
> >> +$(objpfx)tst-cleanup-nostart-stop-gc-static.c: tst-cleanup.c
> >> +       cp $< $@
> >> +
> >>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
> >>         $(common-objpfx)libio/; \
> >>
> >
> >"make clean" doesn't remove the generated files. The standard way in glibc
> >is to add a *-static.c source.
>
> I'll use .INTERMEDIATE and $(eval $(call ..))
>
> diff --git a/libio/Makefile b/libio/Makefile
> index 12ce41038f..a9b44f04df 100644
> --- a/libio/Makefile
> +++ b/libio/Makefile
> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>                  $(objpfx)tst-bz24228-mem.out
>   endif
> +
> +tests += tst-cleanup-default tst-cleanup-default-static
> +tests-static += tst-cleanup-default-static
> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
> +
> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
> +endif
>   endif
>
>   include ../Rules
> @@ -224,6 +244,17 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>   endif
>
> +define gen-tst-cleanup
> +$(objpfx)tst-cleanup-$1-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-$1.out
> +       cmp $$^ > $$@; $$(evaluate-test)
> +$(objpfx)tst-cleanup-$1.c: tst-cleanup.c
> +       cp $$< $$@
> +.INTERMEDIATE: $(objpfx)tst-cleanup-$1.c
> +endef
> +
> +$(foreach t, default default-static start-stop-gc start-stop-gc-static nostart-stop-gc nostart-stop-gc-static, \
> +  $(eval $(call gen-tst-cleanup,$(t))))
> +
>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>         $(common-objpfx)libio/; \

There are 2 issues with static tests:

1. A separate static source is needed.
2. We need to add the static test to both tests and tests-static.

If you want to add a separate static source, you can submit a separate patch
to address these 2 issues together.
  

On 2021-04-04, H.J. Lu wrote:
>On Sat, Apr 3, 2021 at 2:57 PM Fangrui Song <maskray@google.com> wrote:
>>
>> On 2021-04-03, H.J. Lu wrote:
>> >On Sat, Apr 3, 2021 at 11:02 AM Fangrui Song <maskray@google.com> wrote:
>> >>
>> >>
>> >> On 2021-04-02, H.J. Lu wrote:
>> >> >On Thu, Apr 1, 2021 at 8:23 PM Fangrui Song <maskray@google.com> wrote:
>> >> >>
>> >> >> On 2021-04-01, H.J. Lu wrote:
>> >> >> >On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song <maskray@google.com> wrote:
>> >> >> >>
>> >> >> >> So that text_set_element/data_set_element/bss_set_element defined
>> >> >> >> variables will be retained by the linker.
>> >> >> >>
>> >> >> >> Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
>> >> >> >> will not be optimized out; 'retain' prevents section garbage collection
>> >> >> >> if the linker support SHF_GNU_RETAIN.
>> >> >> >>
>> >> >> >> GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
>> >> >> >> identifier name sections to be GCed even if there are live
>> >> >> >> __start_/__stop_ references.
>> >> >> >>
>> >> >> >> Without the change, there are some static linking problems, e.g.
>> >> >> >> _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
>> >> >> >> stdout is not flushed on exit.
>> >> >> >>
>> >> >> >> Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
>> >> >> >> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
>> >> >> >> ---
>> >> >> >> Changes in v1 -> v2:
>> >> >> >> * Define attribute_used_retain_section
>> >> >> >> Changes in v2 -> v3:
>> >> >> >> * Use attribute_used_retain instead attribute_used_retain_section
>> >> >> >> Changes in v3 -> v4:
>> >> >> >> * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
>> >> >> >> Changes in v4 -> v5:
>> >> >> >> * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
>> >> >> >> * Rename *gcc_retain* to *gnu_retain*
>> >> >> >> ---
>> >> >> >>  config.h.in            |  3 +++
>> >> >> >>  configure              | 59 ++++++++++++++++++++++++++++++++++++++++++
>> >> >> >>  configure.ac           | 21 +++++++++++++++
>> >> >> >>  include/libc-symbols.h | 14 +++++++---
>> >> >> >>  libio/Makefile         | 32 +++++++++++++++++++++++
>> >> >> >>  libio/tst-cleanup.c    | 33 +++++++++++++++++++++++
>> >> >> >>  libio/tst-cleanup.exp  |  1 +
>> >> >> >>  7 files changed, 159 insertions(+), 4 deletions(-)
>> >> >> >>  create mode 100644 libio/tst-cleanup.c
>> >> >> >>  create mode 100644 libio/tst-cleanup.exp
>> >> >> >>
>> >> >> >> diff --git a/config.h.in b/config.h.in
>> >> >> >> index ca1547ae67..96a08c7757 100644
>> >> >> >> --- a/config.h.in
>> >> >> >> +++ b/config.h.in
>> >> >> >> @@ -187,6 +187,9 @@
>> >> >> >>  /* Define if gcc supports attribute ifunc.  */
>> >> >> >>  #undef HAVE_GCC_IFUNC
>> >> >> >>
>> >> >> >> +/* Define if CC supports attribute retain.  */
>> >> >> >> +#undef HAVE_GNU_RETAIN
>> >> >> >> +
>> >> >> >>  /* Define if the linker defines __ehdr_start.  */
>> >> >> >>  #undef HAVE_EHDR_START
>> >> >> >>
>> >> >> >> diff --git a/configure b/configure
>> >> >> >> index fcf43bf7de..e64b7f8efe 100755
>> >> >> >> --- a/configure
>> >> >> >> +++ b/configure
>> >> >> >> @@ -4105,6 +4105,31 @@ fi
>> >> >> >>  $as_echo "$libc_cv_textrel_ifunc" >&6; }
>> >> >> >>
>> >> >> >>
>> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
>> >> >> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
>> >> >> >> +if ${libc_cv_gnu_retain+:} false; then :
>> >> >> >> +  $as_echo_n "(cached) " >&6
>> >> >> >> +else
>> >> >> >> +  cat > conftest.c <<EOF
>> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> >> >> +EOF
>> >> >> >> +libc_cv_gnu_retain=no
>> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
>> >> >> >> +   2>&5 ; then
>> >> >> >> +  libc_cv_gnu_retain=yes
>> >> >> >> +fi
>> >> >> >> +rm -f conftest*
>> >> >> >> +fi
>> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
>> >> >> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
>> >> >> >> +if test $libc_cv_gnu_retain = yes; then
>> >> >> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
>> >> >> >> +
>> >> >> >> +fi
>> >> >> >> +config_vars="$config_vars
>> >> >> >> +have-gnu-retain = $libc_cv_gnu_retain"
>> >> >> >> +
>> >> >> >>  # Check if gcc warns about alias for function with incompatible types.
>> >> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
>> >> >> >>  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
>> >> >> >> @@ -5871,6 +5896,40 @@ fi
>> >> >> >>  $as_echo "$libc_linker_feature" >&6; }
>> >> >> >>
>> >> >> >>
>> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
>> >> >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
>> >> >> >> +libc_linker_feature=no
>> >> >> >> +if test x"$gnu_ld" = x"yes"; then
>> >> >> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
>> >> >> >> +  if test -n "$libc_linker_check"; then
>> >> >> >> +    cat > conftest.c <<EOF
>> >> >> >> +int _start (void) { return 42; }
>> >> >> >> +EOF
>> >> >> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
>> >> >> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
>> >> >> >> +                               -fPIC -shared -o conftest.so conftest.c
>> >> >> >> +                               1>&5'
>> >> >> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
>> >> >> >> +  (eval $ac_try) 2>&5
>> >> >> >> +  ac_status=$?
>> >> >> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
>> >> >> >> +  test $ac_status = 0; }; }
>> >> >> >> +    then
>> >> >> >> +      libc_linker_feature=yes
>> >> >> >> +    fi
>> >> >> >> +    rm -f conftest*
>> >> >> >> +  fi
>> >> >> >> +fi
>> >> >> >> +if test $libc_linker_feature = yes; then
>> >> >> >> +  libc_cv_z_start_stop_gc=yes
>> >> >> >> +else
>> >> >> >> +  libc_cv_z_start_stop_gc=no
>> >> >> >> +fi
>> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
>> >> >> >> +$as_echo "$libc_linker_feature" >&6; }
>> >> >> >> +config_vars="$config_vars
>> >> >> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
>> >> >> >> +
>> >> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>> >> >> >>  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>> >> >> >>  libc_linker_feature=no
>> >> >> >> diff --git a/configure.ac b/configure.ac
>> >> >> >> index fce967f2c2..cc47e56e82 100644
>> >> >> >> --- a/configure.ac
>> >> >> >> +++ b/configure.ac
>> >> >> >> @@ -707,6 +707,23 @@ fi
>> >> >> >>  rm -f conftest*])
>> >> >> >>  AC_SUBST(libc_cv_textrel_ifunc)
>> >> >> >>
>> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> >> >> +AC_CACHE_CHECK([for GNU attribute retain support],
>> >> >> >> +              libc_cv_gnu_retain, [dnl
>> >> >> >> +cat > conftest.c <<EOF
>> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> >> >> +EOF
>> >> >> >> +libc_cv_gnu_retain=no
>> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
>> >> >> >> +   2>&AS_MESSAGE_LOG_FD ; then
>> >> >> >> +  libc_cv_gnu_retain=yes
>> >> >> >> +fi
>> >> >> >> +rm -f conftest*])
>> >> >> >> +if test $libc_cv_gnu_retain = yes; then
>> >> >> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
>> >> >> >> +fi
>> >> >> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
>> >> >> >> +
>> >> >> >>  # Check if gcc warns about alias for function with incompatible types.
>> >> >> >>  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>> >> >> >>                libc_cv_gcc_incompatible_alias, [dnl
>> >> >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>> >> >> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>> >> >> >>  AC_SUBST(libc_cv_z_execstack)
>> >> >> >>
>> >> >> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
>> >> >> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
>> >> >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
>> >> >> >> +
>> >> >> >>  LIBC_LINKER_FEATURE([--no-dynamic-linker],
>> >> >> >>                     [-Wl,--no-dynamic-linker],
>> >> >> >>                     [libc_cv_no_dynamic_linker=yes],
>> >> >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
>> >> >> >> index 546fc26a7b..127ea656c2 100644
>> >> >> >> --- a/include/libc-symbols.h
>> >> >> >> +++ b/include/libc-symbols.h
>> >> >> >> @@ -352,6 +352,12 @@ for linking")
>> >> >> >>
>> >> >> >>  */
>> >> >> >>
>> >> >> >> +#ifdef HAVE_GNU_RETAIN
>> >> >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
>> >> >> >> +#else
>> >> >> >> +# define attribute_used_retain __attribute__ ((__used__))
>> >> >> >> +#endif
>> >> >> >> +
>> >> >> >>  /* Symbol set support macros.  */
>> >> >> >>
>> >> >> >>  /* Make SYMBOL, which is in the text segment, an element of SET.  */
>> >> >> >> @@ -367,12 +373,12 @@ for linking")
>> >> >> >>  /* When building a shared library, make the set section writable,
>> >> >> >>     because it will need to be relocated at run time anyway.  */
>> >> >> >>  # define _elf_set_element(set, symbol) \
>> >> >> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
>> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> >> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
>> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >> >> >>  #else
>> >> >> >>  # define _elf_set_element(set, symbol) \
>> >> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> >> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >> >> >>  #endif
>> >> >> >>
>> >> >> >>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
>> >> >> >> diff --git a/libio/Makefile b/libio/Makefile
>> >> >> >> index 12ce41038f..c9c232ebc2 100644
>> >> >> >> --- a/libio/Makefile
>> >> >> >> +++ b/libio/Makefile
>> >> >> >> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared))
>> >> >> >>  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>> >> >> >>                  $(objpfx)tst-bz24228-mem.out
>> >> >> >>  endif
>> >> >> >> +
>> >> >> >> +tests += tst-cleanup-default
>> >> >> >> +tests-static += tst-cleanup-default
>> >> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out
>> >> >> >
>> >> >> >Please make 2 tests,  tst-cleanup-default and tst-cleanup-default-static.
>> >> >>
>> >> >> Added.
>> >> >>
>> >> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> >> >> >> +
>> >> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> >> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
>> >> >> >> +tests-static += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
>> >> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> >> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
>> >> >> >
>> >> >> >Same here.
>> >> >>
>> >> >> Added.
>> >> >>
>> >> >> >> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
>> >> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc
>> >> >> >> +endif
>> >> >> >>  endif
>> >> >> >>
>> >> >> >>  include ../Rules
>> >> >> >> @@ -224,6 +238,24 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>> >> >> >>  $(objpfx)tst-wfile-sync.out: $(gen-locales)
>> >> >> >>  endif
>> >> >> >>
>> >> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> >> >> >> +       cmp $^ > $@; \
>> >> >> >> +       $(evaluate-test)
>> >> >> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
>> >> >> >> +       $(compile.c) -o $@
>> >> >> >> +
>> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> >> >> >> +       cmp $^ > $@; \
>> >> >> >> +       $(evaluate-test)
>> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> >> >> >> +       $(compile.c) -o $@
>> >> >> >> +
>> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
>> >> >> >> +       cmp $^ > $@; \
>> >> >> >> +       $(evaluate-test)
>> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
>> >> >> >> +       $(compile.c) -o $@
>> >> >> >>
>> >> >> >>  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>> >> >> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>> >> >> >>         $(common-objpfx)libio/; \
>> >> >> >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
>> >> >> >> new file mode 100644
>> >> >> >> index 0000000000..7f0a34a91e
>> >> >> >> --- /dev/null
>> >> >> >> +++ b/libio/tst-cleanup.c
>> >> >> >> @@ -0,0 +1,33 @@
>> >> >> >
>> >> >> >Please add a comment saying that test --gc-sections.
>> >> >>
>> >> >> OK, added.
>> >> >>
>> >> >> >> +/* Copyright (C) 2021 Free Software Foundation, Inc.
>> >> >> >> +   This file is part of the GNU C Library.
>> >> >> >> +
>> >> >> >> +   The GNU C Library is free software; you can redistribute it and/or
>> >> >> >> +   modify it under the terms of the GNU Lesser General Public
>> >> >> >> +   License as published by the Free Software Foundation; either
>> >> >> >> +   version 2.1 of the License, or (at your option) any later version.
>> >> >> >> +
>> >> >> >> +   The GNU C Library is distributed in the hope that it will be useful,
>> >> >> >> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>> >> >> >> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> >> >> >> +   Lesser General Public License for more details.
>> >> >> >> +
>> >> >> >> +   You should have received a copy of the GNU Lesser General Public
>> >> >> >> +   License along with the GNU C Library; if not, see
>> >> >> >> +   <https://www.gnu.org/licenses/>.  */
>> >> >> >> +
>> >> >> >> +/* Test that stdout is flushed after atexit callbacks were run.  */
>> >> >> >> +
>> >> >> >> +#include <stdio.h>
>> >> >> >> +#include <stdlib.h>
>> >> >> >> +
>> >> >> >> +void
>> >> >> >> +hook (void)
>> >> >> >> +{
>> >> >> >> +  puts ("hello");
>> >> >> >> +}
>> >> >> >> +
>> >> >> >> +int
>> >> >> >> +main (void)
>> >> >> >> +{
>> >> >> >> +  atexit (hook);
>> >> >> >> +}
>> >> >> >> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
>> >> >> >> new file mode 100644
>> >> >> >> index 0000000000..ce01362503
>> >> >> >> --- /dev/null
>> >> >> >> +++ b/libio/tst-cleanup.exp
>> >> >> >> @@ -0,0 +1 @@
>> >> >> >> +hello
>> >> >> >> --
>> >> >> >> 2.31.0.291.g576ba9dcdaf-goog
>> >> >> >>
>> >> >> >
>> >> >>
>> >> >> diff --git a/config.h.in b/config.h.in
>> >> >> index ca1547ae67..96a08c7757 100644
>> >> >> --- a/config.h.in
>> >> >> +++ b/config.h.in
>> >> >> @@ -187,6 +187,9 @@
>> >> >>   /* Define if gcc supports attribute ifunc.  */
>> >> >>   #undef HAVE_GCC_IFUNC
>> >> >>
>> >> >> +/* Define if CC supports attribute retain.  */
>> >> >> +#undef HAVE_GNU_RETAIN
>> >> >> +
>> >> >>   /* Define if the linker defines __ehdr_start.  */
>> >> >>   #undef HAVE_EHDR_START
>> >> >>
>> >> >> diff --git a/configure b/configure
>> >> >> index fcf43bf7de..e64b7f8efe 100755
>> >> >> --- a/configure
>> >> >> +++ b/configure
>> >> >> @@ -4105,6 +4105,31 @@ fi
>> >> >>   $as_echo "$libc_cv_textrel_ifunc" >&6; }
>> >> >>
>> >> >>
>> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
>> >> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
>> >> >> +if ${libc_cv_gnu_retain+:} false; then :
>> >> >> +  $as_echo_n "(cached) " >&6
>> >> >> +else
>> >> >> +  cat > conftest.c <<EOF
>> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> >> +EOF
>> >> >> +libc_cv_gnu_retain=no
>> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
>> >> >> +   2>&5 ; then
>> >> >> +  libc_cv_gnu_retain=yes
>> >> >> +fi
>> >> >> +rm -f conftest*
>> >> >> +fi
>> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
>> >> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
>> >> >> +if test $libc_cv_gnu_retain = yes; then
>> >> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
>> >> >> +
>> >> >> +fi
>> >> >> +config_vars="$config_vars
>> >> >> +have-gnu-retain = $libc_cv_gnu_retain"
>> >> >> +
>> >> >>   # Check if gcc warns about alias for function with incompatible types.
>> >> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
>> >> >>   $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
>> >> >> @@ -5871,6 +5896,40 @@ fi
>> >> >>   $as_echo "$libc_linker_feature" >&6; }
>> >> >>
>> >> >>
>> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
>> >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
>> >> >> +libc_linker_feature=no
>> >> >> +if test x"$gnu_ld" = x"yes"; then
>> >> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
>> >> >> +  if test -n "$libc_linker_check"; then
>> >> >> +    cat > conftest.c <<EOF
>> >> >> +int _start (void) { return 42; }
>> >> >> +EOF
>> >> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
>> >> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
>> >> >> +                               -fPIC -shared -o conftest.so conftest.c
>> >> >> +                               1>&5'
>> >> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
>> >> >> +  (eval $ac_try) 2>&5
>> >> >> +  ac_status=$?
>> >> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
>> >> >> +  test $ac_status = 0; }; }
>> >> >> +    then
>> >> >> +      libc_linker_feature=yes
>> >> >> +    fi
>> >> >> +    rm -f conftest*
>> >> >> +  fi
>> >> >> +fi
>> >> >> +if test $libc_linker_feature = yes; then
>> >> >> +  libc_cv_z_start_stop_gc=yes
>> >> >> +else
>> >> >> +  libc_cv_z_start_stop_gc=no
>> >> >> +fi
>> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
>> >> >> +$as_echo "$libc_linker_feature" >&6; }
>> >> >> +config_vars="$config_vars
>> >> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
>> >> >> +
>> >> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>> >> >>   $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>> >> >>   libc_linker_feature=no
>> >> >> diff --git a/configure.ac b/configure.ac
>> >> >> index fce967f2c2..cc47e56e82 100644
>> >> >> --- a/configure.ac
>> >> >> +++ b/configure.ac
>> >> >> @@ -707,6 +707,23 @@ fi
>> >> >>   rm -f conftest*])
>> >> >>   AC_SUBST(libc_cv_textrel_ifunc)
>> >> >>
>> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> >> +AC_CACHE_CHECK([for GNU attribute retain support],
>> >> >> +              libc_cv_gnu_retain, [dnl
>> >> >> +cat > conftest.c <<EOF
>> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> >> +EOF
>> >> >> +libc_cv_gnu_retain=no
>> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
>> >> >> +   2>&AS_MESSAGE_LOG_FD ; then
>> >> >> +  libc_cv_gnu_retain=yes
>> >> >> +fi
>> >> >> +rm -f conftest*])
>> >> >> +if test $libc_cv_gnu_retain = yes; then
>> >> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
>> >> >> +fi
>> >> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
>> >> >> +
>> >> >>   # Check if gcc warns about alias for function with incompatible types.
>> >> >>   AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>> >> >>                libc_cv_gcc_incompatible_alias, [dnl
>> >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>> >> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>> >> >>   AC_SUBST(libc_cv_z_execstack)
>> >> >>
>> >> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
>> >> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
>> >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
>> >> >> +
>> >> >>   LIBC_LINKER_FEATURE([--no-dynamic-linker],
>> >> >>                     [-Wl,--no-dynamic-linker],
>> >> >>                     [libc_cv_no_dynamic_linker=yes],
>> >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
>> >> >> index 546fc26a7b..127ea656c2 100644
>> >> >> --- a/include/libc-symbols.h
>> >> >> +++ b/include/libc-symbols.h
>> >> >> @@ -352,6 +352,12 @@ for linking")
>> >> >>
>> >> >>   */
>> >> >>
>> >> >> +#ifdef HAVE_GNU_RETAIN
>> >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
>> >> >> +#else
>> >> >> +# define attribute_used_retain __attribute__ ((__used__))
>> >> >> +#endif
>> >> >> +
>> >> >>   /* Symbol set support macros.  */
>> >> >>
>> >> >>   /* Make SYMBOL, which is in the text segment, an element of SET.  */
>> >> >> @@ -367,12 +373,12 @@ for linking")
>> >> >>   /* When building a shared library, make the set section writable,
>> >> >>      because it will need to be relocated at run time anyway.  */
>> >> >>   # define _elf_set_element(set, symbol) \
>> >> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
>> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
>> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >> >>   #else
>> >> >>   # define _elf_set_element(set, symbol) \
>> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >> >>   #endif
>> >> >>
>> >> >>   /* Define SET as a symbol set.  This may be required (it is in a.out) to
>> >> >> diff --git a/libio/Makefile b/libio/Makefile
>> >> >> index 12ce41038f..ad0d53bb49 100644
>> >> >> --- a/libio/Makefile
>> >> >> +++ b/libio/Makefile
>> >> >> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
>> >> >>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>> >> >>                  $(objpfx)tst-bz24228-mem.out
>> >> >>   endif
>> >> >> +
>> >> >> +tests += tst-cleanup-default tst-cleanup-default-static
>> >> >> +tests-static += tst-cleanup-default-static
>> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
>> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> >> >> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
>> >> >> +
>> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
>> >> >> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
>> >> >> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
>> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> >> >> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
>> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
>> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
>> >> >> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
>> >> >> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
>> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
>> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
>> >> >> +endif
>> >> >>   endif
>> >> >>
>> >> >>   include ../Rules
>> >> >> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>> >> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>> >> >>   endif
>> >> >>
>> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> >> >> +       cmp $^ > $@; \
>> >> >> +       $(evaluate-test)
>> >> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
>> >> >> +       $(compile.c) -o $@
>> >> >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
>> >> >> +       cmp $^ > $@; \
>> >> >> +       $(evaluate-test)
>> >> >> +$(objpfx)tst-cleanup-default-static.o: tst-cleanup.c
>> >> >> +       $(compile.c) -o $@
>> >> >> +
>> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> >> >> +       cmp $^ > $@; \
>> >> >> +       $(evaluate-test)
>> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> >> >> +       $(compile.c) -o $@
>> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
>> >> >> +       cmp $^ > $@; \
>> >> >> +       $(evaluate-test)
>> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c
>> >> >> +       $(compile.c) -o $@
>> >> >
>> >> >Please add a separate .c file for each test to get the correct dependency.
>> >>
>> >> Changed this block to:
>> >>
>> >> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>> >>   endif
>> >>
>> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-default.c: tst-cleanup.c
>> >> +       cp $< $@
>> >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-default-static.c: tst-cleanup.c
>> >> +       cp $< $@
>> >> +
>> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> >> +       $(compile.c) -o $@
>> >> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-start-stop-gc-static.c: tst-cleanup.c
>> >> +       cp $< $@
>> >> +
>> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-nostart-stop-gc.c: tst-cleanup.c
>> >> +       cp $< $@
>> >> +$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc-static.out
>> >> +       cmp $^ > $@; \
>> >> +       $(evaluate-test)
>> >> +$(objpfx)tst-cleanup-nostart-stop-gc-static.c: tst-cleanup.c
>> >> +       cp $< $@
>> >> +
>> >>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>> >>         $(common-objpfx)libio/; \
>> >>
>> >
>> >"make clean" doesn't remove the generated files. The standard way in glibc
>> >is to add a *-static.c source.
>>
>> I'll use .INTERMEDIATE and $(eval $(call ..))
>>
>> diff --git a/libio/Makefile b/libio/Makefile
>> index 12ce41038f..a9b44f04df 100644
>> --- a/libio/Makefile
>> +++ b/libio/Makefile
>> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
>>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>>                  $(objpfx)tst-bz24228-mem.out
>>   endif
>> +
>> +tests += tst-cleanup-default tst-cleanup-default-static
>> +tests-static += tst-cleanup-default-static
>> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
>> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
>> +
>> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
>> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
>> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
>> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
>> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
>> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
>> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
>> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
>> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
>> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
>> +endif
>>   endif
>>
>>   include ../Rules
>> @@ -224,6 +244,17 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>>   endif
>>
>> +define gen-tst-cleanup
>> +$(objpfx)tst-cleanup-$1-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-$1.out
>> +       cmp $$^ > $$@; $$(evaluate-test)
>> +$(objpfx)tst-cleanup-$1.c: tst-cleanup.c
>> +       cp $$< $$@
>> +.INTERMEDIATE: $(objpfx)tst-cleanup-$1.c
>> +endef
>> +
>> +$(foreach t, default default-static start-stop-gc start-stop-gc-static nostart-stop-gc nostart-stop-gc-static, \
>> +  $(eval $(call gen-tst-cleanup,$(t))))
>> +
>>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>>         $(common-objpfx)libio/; \
>
>There are 2 issues with static tests:
>
>1. A separate static source is needed.

.INTERMEDIATE perfectly solves the lingering copied source issue.
I don't see lingering libio/tst-cleanup-*.c

>2. We need to add the static test to both tests and tests-static.

tests-static suffices. I have checked some tests-static usage in other
directories.

I have additionally checked that:

* touch libc.a => next invocation `make -r -C ~/Dev/glibc/libio objdir=$PWD check -j 20` will rebuild the static tests
* touch libc.so => next invocation `make -r -C ~/Dev/glibc/libio objdir=$PWD check -j 20` will rebuild the dynamic tests
* rm libio/tst-cleanup-default-cmp.out => next invocation `make -r -C ~/Dev/glibc/libio objdir=$PWD check -j 20` will rerun the single test

>If you want to add a separate static source, you can submit a separate patch
>to address these 2 issues together.
  

On Mon, Apr 5, 2021 at 11:17 AM Fangrui Song <maskray@google.com> wrote:
>
> On 2021-04-04, H.J. Lu wrote:
> >On Sat, Apr 3, 2021 at 2:57 PM Fangrui Song <maskray@google.com> wrote:
> >>
> >> On 2021-04-03, H.J. Lu wrote:
> >> >On Sat, Apr 3, 2021 at 11:02 AM Fangrui Song <maskray@google.com> wrote:
> >> >>
> >> >>
> >> >> On 2021-04-02, H.J. Lu wrote:
> >> >> >On Thu, Apr 1, 2021 at 8:23 PM Fangrui Song <maskray@google.com> wrote:
> >> >> >>
> >> >> >> On 2021-04-01, H.J. Lu wrote:
> >> >> >> >On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song <maskray@google.com> wrote:
> >> >> >> >>
> >> >> >> >> So that text_set_element/data_set_element/bss_set_element defined
> >> >> >> >> variables will be retained by the linker.
> >> >> >> >>
> >> >> >> >> Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
> >> >> >> >> will not be optimized out; 'retain' prevents section garbage collection
> >> >> >> >> if the linker support SHF_GNU_RETAIN.
> >> >> >> >>
> >> >> >> >> GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
> >> >> >> >> identifier name sections to be GCed even if there are live
> >> >> >> >> __start_/__stop_ references.
> >> >> >> >>
> >> >> >> >> Without the change, there are some static linking problems, e.g.
> >> >> >> >> _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
> >> >> >> >> stdout is not flushed on exit.
> >> >> >> >>
> >> >> >> >> Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
> >> >> >> >> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
> >> >> >> >> ---
> >> >> >> >> Changes in v1 -> v2:
> >> >> >> >> * Define attribute_used_retain_section
> >> >> >> >> Changes in v2 -> v3:
> >> >> >> >> * Use attribute_used_retain instead attribute_used_retain_section
> >> >> >> >> Changes in v3 -> v4:
> >> >> >> >> * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
> >> >> >> >> Changes in v4 -> v5:
> >> >> >> >> * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
> >> >> >> >> * Rename *gcc_retain* to *gnu_retain*
> >> >> >> >> ---
> >> >> >> >>  config.h.in            |  3 +++
> >> >> >> >>  configure              | 59 ++++++++++++++++++++++++++++++++++++++++++
> >> >> >> >>  configure.ac           | 21 +++++++++++++++
> >> >> >> >>  include/libc-symbols.h | 14 +++++++---
> >> >> >> >>  libio/Makefile         | 32 +++++++++++++++++++++++
> >> >> >> >>  libio/tst-cleanup.c    | 33 +++++++++++++++++++++++
> >> >> >> >>  libio/tst-cleanup.exp  |  1 +
> >> >> >> >>  7 files changed, 159 insertions(+), 4 deletions(-)
> >> >> >> >>  create mode 100644 libio/tst-cleanup.c
> >> >> >> >>  create mode 100644 libio/tst-cleanup.exp
> >> >> >> >>
> >> >> >> >> diff --git a/config.h.in b/config.h.in
> >> >> >> >> index ca1547ae67..96a08c7757 100644
> >> >> >> >> --- a/config.h.in
> >> >> >> >> +++ b/config.h.in
> >> >> >> >> @@ -187,6 +187,9 @@
> >> >> >> >>  /* Define if gcc supports attribute ifunc.  */
> >> >> >> >>  #undef HAVE_GCC_IFUNC
> >> >> >> >>
> >> >> >> >> +/* Define if CC supports attribute retain.  */
> >> >> >> >> +#undef HAVE_GNU_RETAIN
> >> >> >> >> +
> >> >> >> >>  /* Define if the linker defines __ehdr_start.  */
> >> >> >> >>  #undef HAVE_EHDR_START
> >> >> >> >>
> >> >> >> >> diff --git a/configure b/configure
> >> >> >> >> index fcf43bf7de..e64b7f8efe 100755
> >> >> >> >> --- a/configure
> >> >> >> >> +++ b/configure
> >> >> >> >> @@ -4105,6 +4105,31 @@ fi
> >> >> >> >>  $as_echo "$libc_cv_textrel_ifunc" >&6; }
> >> >> >> >>
> >> >> >> >>
> >> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
> >> >> >> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
> >> >> >> >> +if ${libc_cv_gnu_retain+:} false; then :
> >> >> >> >> +  $as_echo_n "(cached) " >&6
> >> >> >> >> +else
> >> >> >> >> +  cat > conftest.c <<EOF
> >> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> >> >> +EOF
> >> >> >> >> +libc_cv_gnu_retain=no
> >> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> >> >> >> >> +   2>&5 ; then
> >> >> >> >> +  libc_cv_gnu_retain=yes
> >> >> >> >> +fi
> >> >> >> >> +rm -f conftest*
> >> >> >> >> +fi
> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
> >> >> >> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
> >> >> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> >> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
> >> >> >> >> +
> >> >> >> >> +fi
> >> >> >> >> +config_vars="$config_vars
> >> >> >> >> +have-gnu-retain = $libc_cv_gnu_retain"
> >> >> >> >> +
> >> >> >> >>  # Check if gcc warns about alias for function with incompatible types.
> >> >> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
> >> >> >> >>  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
> >> >> >> >> @@ -5871,6 +5896,40 @@ fi
> >> >> >> >>  $as_echo "$libc_linker_feature" >&6; }
> >> >> >> >>
> >> >> >> >>
> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
> >> >> >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
> >> >> >> >> +libc_linker_feature=no
> >> >> >> >> +if test x"$gnu_ld" = x"yes"; then
> >> >> >> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
> >> >> >> >> +  if test -n "$libc_linker_check"; then
> >> >> >> >> +    cat > conftest.c <<EOF
> >> >> >> >> +int _start (void) { return 42; }
> >> >> >> >> +EOF
> >> >> >> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> >> >> >> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
> >> >> >> >> +                               -fPIC -shared -o conftest.so conftest.c
> >> >> >> >> +                               1>&5'
> >> >> >> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> >> >> >> >> +  (eval $ac_try) 2>&5
> >> >> >> >> +  ac_status=$?
> >> >> >> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> >> >> >> >> +  test $ac_status = 0; }; }
> >> >> >> >> +    then
> >> >> >> >> +      libc_linker_feature=yes
> >> >> >> >> +    fi
> >> >> >> >> +    rm -f conftest*
> >> >> >> >> +  fi
> >> >> >> >> +fi
> >> >> >> >> +if test $libc_linker_feature = yes; then
> >> >> >> >> +  libc_cv_z_start_stop_gc=yes
> >> >> >> >> +else
> >> >> >> >> +  libc_cv_z_start_stop_gc=no
> >> >> >> >> +fi
> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> >> >> >> >> +$as_echo "$libc_linker_feature" >&6; }
> >> >> >> >> +config_vars="$config_vars
> >> >> >> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
> >> >> >> >> +
> >> >> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
> >> >> >> >>  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
> >> >> >> >>  libc_linker_feature=no
> >> >> >> >> diff --git a/configure.ac b/configure.ac
> >> >> >> >> index fce967f2c2..cc47e56e82 100644
> >> >> >> >> --- a/configure.ac
> >> >> >> >> +++ b/configure.ac
> >> >> >> >> @@ -707,6 +707,23 @@ fi
> >> >> >> >>  rm -f conftest*])
> >> >> >> >>  AC_SUBST(libc_cv_textrel_ifunc)
> >> >> >> >>
> >> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> >> >> +AC_CACHE_CHECK([for GNU attribute retain support],
> >> >> >> >> +              libc_cv_gnu_retain, [dnl
> >> >> >> >> +cat > conftest.c <<EOF
> >> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> >> >> +EOF
> >> >> >> >> +libc_cv_gnu_retain=no
> >> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
> >> >> >> >> +   2>&AS_MESSAGE_LOG_FD ; then
> >> >> >> >> +  libc_cv_gnu_retain=yes
> >> >> >> >> +fi
> >> >> >> >> +rm -f conftest*])
> >> >> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> >> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
> >> >> >> >> +fi
> >> >> >> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
> >> >> >> >> +
> >> >> >> >>  # Check if gcc warns about alias for function with incompatible types.
> >> >> >> >>  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
> >> >> >> >>                libc_cv_gcc_incompatible_alias, [dnl
> >> >> >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
> >> >> >> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
> >> >> >> >>  AC_SUBST(libc_cv_z_execstack)
> >> >> >> >>
> >> >> >> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> >> >> >> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> >> >> >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
> >> >> >> >> +
> >> >> >> >>  LIBC_LINKER_FEATURE([--no-dynamic-linker],
> >> >> >> >>                     [-Wl,--no-dynamic-linker],
> >> >> >> >>                     [libc_cv_no_dynamic_linker=yes],
> >> >> >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
> >> >> >> >> index 546fc26a7b..127ea656c2 100644
> >> >> >> >> --- a/include/libc-symbols.h
> >> >> >> >> +++ b/include/libc-symbols.h
> >> >> >> >> @@ -352,6 +352,12 @@ for linking")
> >> >> >> >>
> >> >> >> >>  */
> >> >> >> >>
> >> >> >> >> +#ifdef HAVE_GNU_RETAIN
> >> >> >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
> >> >> >> >> +#else
> >> >> >> >> +# define attribute_used_retain __attribute__ ((__used__))
> >> >> >> >> +#endif
> >> >> >> >> +
> >> >> >> >>  /* Symbol set support macros.  */
> >> >> >> >>
> >> >> >> >>  /* Make SYMBOL, which is in the text segment, an element of SET.  */
> >> >> >> >> @@ -367,12 +373,12 @@ for linking")
> >> >> >> >>  /* When building a shared library, make the set section writable,
> >> >> >> >>     because it will need to be relocated at run time anyway.  */
> >> >> >> >>  # define _elf_set_element(set, symbol) \
> >> >> >> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> >> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >> >> >>  #else
> >> >> >> >>  # define _elf_set_element(set, symbol) \
> >> >> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> >> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >> >> >>  #endif
> >> >> >> >>
> >> >> >> >>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
> >> >> >> >> diff --git a/libio/Makefile b/libio/Makefile
> >> >> >> >> index 12ce41038f..c9c232ebc2 100644
> >> >> >> >> --- a/libio/Makefile
> >> >> >> >> +++ b/libio/Makefile
> >> >> >> >> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared))
> >> >> >> >>  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
> >> >> >> >>                  $(objpfx)tst-bz24228-mem.out
> >> >> >> >>  endif
> >> >> >> >> +
> >> >> >> >> +tests += tst-cleanup-default
> >> >> >> >> +tests-static += tst-cleanup-default
> >> >> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out
> >> >> >> >
> >> >> >> >Please make 2 tests,  tst-cleanup-default and tst-cleanup-default-static.
> >> >> >>
> >> >> >> Added.
> >> >> >>
> >> >> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> >> >> >> >> +
> >> >> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> >> >> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> >> >> >> >> +tests-static += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> >> >> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> >> >> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
> >> >> >> >
> >> >> >> >Same here.
> >> >> >>
> >> >> >> Added.
> >> >> >>
> >> >> >> >> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
> >> >> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc
> >> >> >> >> +endif
> >> >> >> >>  endif
> >> >> >> >>
> >> >> >> >>  include ../Rules
> >> >> >> >> @@ -224,6 +238,24 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >> >> >> >>  $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >> >> >> >>  endif
> >> >> >> >>
> >> >> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> >> >> >> >> +       cmp $^ > $@; \
> >> >> >> >> +       $(evaluate-test)
> >> >> >> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
> >> >> >> >> +       $(compile.c) -o $@
> >> >> >> >> +
> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> >> >> >> >> +       cmp $^ > $@; \
> >> >> >> >> +       $(evaluate-test)
> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> >> >> >> >> +       $(compile.c) -o $@
> >> >> >> >> +
> >> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
> >> >> >> >> +       cmp $^ > $@; \
> >> >> >> >> +       $(evaluate-test)
> >> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
> >> >> >> >> +       $(compile.c) -o $@
> >> >> >> >>
> >> >> >> >>  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
> >> >> >> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
> >> >> >> >>         $(common-objpfx)libio/; \
> >> >> >> >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
> >> >> >> >> new file mode 100644
> >> >> >> >> index 0000000000..7f0a34a91e
> >> >> >> >> --- /dev/null
> >> >> >> >> +++ b/libio/tst-cleanup.c
> >> >> >> >> @@ -0,0 +1,33 @@
> >> >> >> >
> >> >> >> >Please add a comment saying that test --gc-sections.
> >> >> >>
> >> >> >> OK, added.
> >> >> >>
> >> >> >> >> +/* Copyright (C) 2021 Free Software Foundation, Inc.
> >> >> >> >> +   This file is part of the GNU C Library.
> >> >> >> >> +
> >> >> >> >> +   The GNU C Library is free software; you can redistribute it and/or
> >> >> >> >> +   modify it under the terms of the GNU Lesser General Public
> >> >> >> >> +   License as published by the Free Software Foundation; either
> >> >> >> >> +   version 2.1 of the License, or (at your option) any later version.
> >> >> >> >> +
> >> >> >> >> +   The GNU C Library is distributed in the hope that it will be useful,
> >> >> >> >> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> >> >> >> >> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> >> >> >> >> +   Lesser General Public License for more details.
> >> >> >> >> +
> >> >> >> >> +   You should have received a copy of the GNU Lesser General Public
> >> >> >> >> +   License along with the GNU C Library; if not, see
> >> >> >> >> +   <https://www.gnu.org/licenses/>.  */
> >> >> >> >> +
> >> >> >> >> +/* Test that stdout is flushed after atexit callbacks were run.  */
> >> >> >> >> +
> >> >> >> >> +#include <stdio.h>
> >> >> >> >> +#include <stdlib.h>
> >> >> >> >> +
> >> >> >> >> +void
> >> >> >> >> +hook (void)
> >> >> >> >> +{
> >> >> >> >> +  puts ("hello");
> >> >> >> >> +}
> >> >> >> >> +
> >> >> >> >> +int
> >> >> >> >> +main (void)
> >> >> >> >> +{
> >> >> >> >> +  atexit (hook);
> >> >> >> >> +}
> >> >> >> >> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
> >> >> >> >> new file mode 100644
> >> >> >> >> index 0000000000..ce01362503
> >> >> >> >> --- /dev/null
> >> >> >> >> +++ b/libio/tst-cleanup.exp
> >> >> >> >> @@ -0,0 +1 @@
> >> >> >> >> +hello
> >> >> >> >> --
> >> >> >> >> 2.31.0.291.g576ba9dcdaf-goog
> >> >> >> >>
> >> >> >> >
> >> >> >>
> >> >> >> diff --git a/config.h.in b/config.h.in
> >> >> >> index ca1547ae67..96a08c7757 100644
> >> >> >> --- a/config.h.in
> >> >> >> +++ b/config.h.in
> >> >> >> @@ -187,6 +187,9 @@
> >> >> >>   /* Define if gcc supports attribute ifunc.  */
> >> >> >>   #undef HAVE_GCC_IFUNC
> >> >> >>
> >> >> >> +/* Define if CC supports attribute retain.  */
> >> >> >> +#undef HAVE_GNU_RETAIN
> >> >> >> +
> >> >> >>   /* Define if the linker defines __ehdr_start.  */
> >> >> >>   #undef HAVE_EHDR_START
> >> >> >>
> >> >> >> diff --git a/configure b/configure
> >> >> >> index fcf43bf7de..e64b7f8efe 100755
> >> >> >> --- a/configure
> >> >> >> +++ b/configure
> >> >> >> @@ -4105,6 +4105,31 @@ fi
> >> >> >>   $as_echo "$libc_cv_textrel_ifunc" >&6; }
> >> >> >>
> >> >> >>
> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
> >> >> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
> >> >> >> +if ${libc_cv_gnu_retain+:} false; then :
> >> >> >> +  $as_echo_n "(cached) " >&6
> >> >> >> +else
> >> >> >> +  cat > conftest.c <<EOF
> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> >> +EOF
> >> >> >> +libc_cv_gnu_retain=no
> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> >> >> >> +   2>&5 ; then
> >> >> >> +  libc_cv_gnu_retain=yes
> >> >> >> +fi
> >> >> >> +rm -f conftest*
> >> >> >> +fi
> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
> >> >> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
> >> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
> >> >> >> +
> >> >> >> +fi
> >> >> >> +config_vars="$config_vars
> >> >> >> +have-gnu-retain = $libc_cv_gnu_retain"
> >> >> >> +
> >> >> >>   # Check if gcc warns about alias for function with incompatible types.
> >> >> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
> >> >> >>   $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
> >> >> >> @@ -5871,6 +5896,40 @@ fi
> >> >> >>   $as_echo "$libc_linker_feature" >&6; }
> >> >> >>
> >> >> >>
> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
> >> >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
> >> >> >> +libc_linker_feature=no
> >> >> >> +if test x"$gnu_ld" = x"yes"; then
> >> >> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
> >> >> >> +  if test -n "$libc_linker_check"; then
> >> >> >> +    cat > conftest.c <<EOF
> >> >> >> +int _start (void) { return 42; }
> >> >> >> +EOF
> >> >> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> >> >> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
> >> >> >> +                               -fPIC -shared -o conftest.so conftest.c
> >> >> >> +                               1>&5'
> >> >> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> >> >> >> +  (eval $ac_try) 2>&5
> >> >> >> +  ac_status=$?
> >> >> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> >> >> >> +  test $ac_status = 0; }; }
> >> >> >> +    then
> >> >> >> +      libc_linker_feature=yes
> >> >> >> +    fi
> >> >> >> +    rm -f conftest*
> >> >> >> +  fi
> >> >> >> +fi
> >> >> >> +if test $libc_linker_feature = yes; then
> >> >> >> +  libc_cv_z_start_stop_gc=yes
> >> >> >> +else
> >> >> >> +  libc_cv_z_start_stop_gc=no
> >> >> >> +fi
> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> >> >> >> +$as_echo "$libc_linker_feature" >&6; }
> >> >> >> +config_vars="$config_vars
> >> >> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
> >> >> >> +
> >> >> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
> >> >> >>   $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
> >> >> >>   libc_linker_feature=no
> >> >> >> diff --git a/configure.ac b/configure.ac
> >> >> >> index fce967f2c2..cc47e56e82 100644
> >> >> >> --- a/configure.ac
> >> >> >> +++ b/configure.ac
> >> >> >> @@ -707,6 +707,23 @@ fi
> >> >> >>   rm -f conftest*])
> >> >> >>   AC_SUBST(libc_cv_textrel_ifunc)
> >> >> >>
> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> >> +AC_CACHE_CHECK([for GNU attribute retain support],
> >> >> >> +              libc_cv_gnu_retain, [dnl
> >> >> >> +cat > conftest.c <<EOF
> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> >> +EOF
> >> >> >> +libc_cv_gnu_retain=no
> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
> >> >> >> +   2>&AS_MESSAGE_LOG_FD ; then
> >> >> >> +  libc_cv_gnu_retain=yes
> >> >> >> +fi
> >> >> >> +rm -f conftest*])
> >> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
> >> >> >> +fi
> >> >> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
> >> >> >> +
> >> >> >>   # Check if gcc warns about alias for function with incompatible types.
> >> >> >>   AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
> >> >> >>                libc_cv_gcc_incompatible_alias, [dnl
> >> >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
> >> >> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
> >> >> >>   AC_SUBST(libc_cv_z_execstack)
> >> >> >>
> >> >> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> >> >> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> >> >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
> >> >> >> +
> >> >> >>   LIBC_LINKER_FEATURE([--no-dynamic-linker],
> >> >> >>                     [-Wl,--no-dynamic-linker],
> >> >> >>                     [libc_cv_no_dynamic_linker=yes],
> >> >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
> >> >> >> index 546fc26a7b..127ea656c2 100644
> >> >> >> --- a/include/libc-symbols.h
> >> >> >> +++ b/include/libc-symbols.h
> >> >> >> @@ -352,6 +352,12 @@ for linking")
> >> >> >>
> >> >> >>   */
> >> >> >>
> >> >> >> +#ifdef HAVE_GNU_RETAIN
> >> >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
> >> >> >> +#else
> >> >> >> +# define attribute_used_retain __attribute__ ((__used__))
> >> >> >> +#endif
> >> >> >> +
> >> >> >>   /* Symbol set support macros.  */
> >> >> >>
> >> >> >>   /* Make SYMBOL, which is in the text segment, an element of SET.  */
> >> >> >> @@ -367,12 +373,12 @@ for linking")
> >> >> >>   /* When building a shared library, make the set section writable,
> >> >> >>      because it will need to be relocated at run time anyway.  */
> >> >> >>   # define _elf_set_element(set, symbol) \
> >> >> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >> >>   #else
> >> >> >>   # define _elf_set_element(set, symbol) \
> >> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >> >>   #endif
> >> >> >>
> >> >> >>   /* Define SET as a symbol set.  This may be required (it is in a.out) to
> >> >> >> diff --git a/libio/Makefile b/libio/Makefile
> >> >> >> index 12ce41038f..ad0d53bb49 100644
> >> >> >> --- a/libio/Makefile
> >> >> >> +++ b/libio/Makefile
> >> >> >> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
> >> >> >>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
> >> >> >>                  $(objpfx)tst-bz24228-mem.out
> >> >> >>   endif
> >> >> >> +
> >> >> >> +tests += tst-cleanup-default tst-cleanup-default-static
> >> >> >> +tests-static += tst-cleanup-default-static
> >> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
> >> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> >> >> >> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
> >> >> >> +
> >> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> >> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
> >> >> >> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
> >> >> >> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
> >> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> >> >> >> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
> >> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
> >> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
> >> >> >> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
> >> >> >> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
> >> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
> >> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
> >> >> >> +endif
> >> >> >>   endif
> >> >> >>
> >> >> >>   include ../Rules
> >> >> >> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >> >> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >> >> >>   endif
> >> >> >>
> >> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> >> >> >> +       cmp $^ > $@; \
> >> >> >> +       $(evaluate-test)
> >> >> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
> >> >> >> +       $(compile.c) -o $@
> >> >> >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
> >> >> >> +       cmp $^ > $@; \
> >> >> >> +       $(evaluate-test)
> >> >> >> +$(objpfx)tst-cleanup-default-static.o: tst-cleanup.c
> >> >> >> +       $(compile.c) -o $@
> >> >> >> +
> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> >> >> >> +       cmp $^ > $@; \
> >> >> >> +       $(evaluate-test)
> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> >> >> >> +       $(compile.c) -o $@
> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
> >> >> >> +       cmp $^ > $@; \
> >> >> >> +       $(evaluate-test)
> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c
> >> >> >> +       $(compile.c) -o $@
> >> >> >
> >> >> >Please add a separate .c file for each test to get the correct dependency.
> >> >>
> >> >> Changed this block to:
> >> >>
> >> >> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >> >>   endif
> >> >>
> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-default.c: tst-cleanup.c
> >> >> +       cp $< $@
> >> >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-default-static.c: tst-cleanup.c
> >> >> +       cp $< $@
> >> >> +
> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> >> >> +       $(compile.c) -o $@
> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static.c: tst-cleanup.c
> >> >> +       cp $< $@
> >> >> +
> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc.c: tst-cleanup.c
> >> >> +       cp $< $@
> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc-static.out
> >> >> +       cmp $^ > $@; \
> >> >> +       $(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-static.c: tst-cleanup.c
> >> >> +       cp $< $@
> >> >> +
> >> >>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
> >> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
> >> >>         $(common-objpfx)libio/; \
> >> >>
> >> >
> >> >"make clean" doesn't remove the generated files. The standard way in glibc
> >> >is to add a *-static.c source.
> >>
> >> I'll use .INTERMEDIATE and $(eval $(call ..))
> >>
> >> diff --git a/libio/Makefile b/libio/Makefile
> >> index 12ce41038f..a9b44f04df 100644
> >> --- a/libio/Makefile
> >> +++ b/libio/Makefile
> >> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
> >>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
> >>                  $(objpfx)tst-bz24228-mem.out
> >>   endif
> >> +
> >> +tests += tst-cleanup-default tst-cleanup-default-static
> >> +tests-static += tst-cleanup-default-static
> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> >> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
> >> +
> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
> >> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
> >> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> >> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
> >> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
> >> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
> >> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
> >> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
> >> +endif
> >>   endif
> >>
> >>   include ../Rules
> >> @@ -224,6 +244,17 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >>   endif
> >>
> >> +define gen-tst-cleanup
> >> +$(objpfx)tst-cleanup-$1-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-$1.out
> >> +       cmp $$^ > $$@; $$(evaluate-test)
> >> +$(objpfx)tst-cleanup-$1.c: tst-cleanup.c
> >> +       cp $$< $$@
> >> +.INTERMEDIATE: $(objpfx)tst-cleanup-$1.c
> >> +endef
> >> +
> >> +$(foreach t, default default-static start-stop-gc start-stop-gc-static nostart-stop-gc nostart-stop-gc-static, \
> >> +  $(eval $(call gen-tst-cleanup,$(t))))
> >> +
> >>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
> >>         $(common-objpfx)libio/; \
> >
> >There are 2 issues with static tests:
> >
> >1. A separate static source is needed.
>
> .INTERMEDIATE perfectly solves the lingering copied source issue.
> I don't see lingering libio/tst-cleanup-*.c

I was referring to

elf/tst-array1-static.c
elf/tst-array5-static.c
elf/tst-dl-iter-static.c
elf/tst-dst-static.c
elf/tst-leaks1-static.c
elf/tst-libc_dlvsym-static.c
elf/tst-linkall-static.c
elf/tst-ptrguard1-static.c
elf/tst-single_threaded-pthread-static.c
elf/tst-single_threaded-static.c
elf/tst-stackguard1-static.c
elf/tst-tls1-static.c
elf/tst-tls2-static.c
elf/tst-tls9-static.c
elf/tst-tlsalign-extern-static.c
elf/tst-tlsalign-static.c
gmon/tst-gmon-static.c
gmon/tst-profile-static.c
localedata/bug-setlocale1-static.c
localedata/tst-langinfo-newlocale-static.c
localedata/tst-langinfo-setlocale-static.c
localedata/tst-langinfo-static.c
malloc/tst-malloc-usable-static.c
math/test-fpucw-ieee-static.c
math/test-fpucw-static.c
math/test-signgam-uchar-init-static.c
math/test-signgam-uchar-static.c
math/test-signgam-uint-init-static.c
math/test-signgam-uint-static.c
math/test-signgam-ullong-init-static.c
math/test-signgam-ullong-static.c
nptl/tst-mutex8-static.c
nptl/tst-mutexpi8-static.c
nptl/tst-sem11-static.c
nptl/tst-sem12-static.c
nptl/tst-setuid1-static.c
nptl/tst-stackguard1-static.c
nss/tst-nss-static.c
posix/tst-exec-static.c
posix/tst-spawn-static.c
setjmp/tst-setjmp-static.c

> >2. We need to add the static test to both tests and tests-static.
>
> tests-static suffices. I have checked some tests-static usage in other
> directories.

There are

tests           := tst-setjmp jmpbug bug269-setjmp tst-setjmp-fp \
                   tst-sigsetjmp tst-setjmp-static
tests-static    := tst-setjmp-static

They should be replaced by something like

tests           := tst-setjmp jmpbug bug269-setjmp tst-setjmp-fp \
                   tst-sigsetjmp
tests-static-add := tst-setjmp-static

> I have additionally checked that:
>
> * touch libc.a => next invocation `make -r -C ~/Dev/glibc/libio objdir=$PWD check -j 20` will rebuild the static tests
> * touch libc.so => next invocation `make -r -C ~/Dev/glibc/libio objdir=$PWD check -j 20` will rebuild the dynamic tests
> * rm libio/tst-cleanup-default-cmp.out => next invocation `make -r -C ~/Dev/glibc/libio objdir=$PWD check -j 20` will rerun the single test
>
> >If you want to add a separate static source, you can submit a separate patch
> >to address these 2 issues together.
  

On 2021-04-05, H.J. Lu wrote:
>On Mon, Apr 5, 2021 at 11:17 AM Fangrui Song <maskray@google.com> wrote:
>>
>> On 2021-04-04, H.J. Lu wrote:
>> >On Sat, Apr 3, 2021 at 2:57 PM Fangrui Song <maskray@google.com> wrote:
>> >>
>> >> On 2021-04-03, H.J. Lu wrote:
>> >> >On Sat, Apr 3, 2021 at 11:02 AM Fangrui Song <maskray@google.com> wrote:
>> >> >>
>> >> >>
>> >> >> On 2021-04-02, H.J. Lu wrote:
>> >> >> >On Thu, Apr 1, 2021 at 8:23 PM Fangrui Song <maskray@google.com> wrote:
>> >> >> >>
>> >> >> >> On 2021-04-01, H.J. Lu wrote:
>> >> >> >> >On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song <maskray@google.com> wrote:
>> >> >> >> >>
>> >> >> >> >> So that text_set_element/data_set_element/bss_set_element defined
>> >> >> >> >> variables will be retained by the linker.
>> >> >> >> >>
>> >> >> >> >> Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
>> >> >> >> >> will not be optimized out; 'retain' prevents section garbage collection
>> >> >> >> >> if the linker support SHF_GNU_RETAIN.
>> >> >> >> >>
>> >> >> >> >> GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
>> >> >> >> >> identifier name sections to be GCed even if there are live
>> >> >> >> >> __start_/__stop_ references.
>> >> >> >> >>
>> >> >> >> >> Without the change, there are some static linking problems, e.g.
>> >> >> >> >> _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
>> >> >> >> >> stdout is not flushed on exit.
>> >> >> >> >>
>> >> >> >> >> Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
>> >> >> >> >> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
>> >> >> >> >> ---
>> >> >> >> >> Changes in v1 -> v2:
>> >> >> >> >> * Define attribute_used_retain_section
>> >> >> >> >> Changes in v2 -> v3:
>> >> >> >> >> * Use attribute_used_retain instead attribute_used_retain_section
>> >> >> >> >> Changes in v3 -> v4:
>> >> >> >> >> * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
>> >> >> >> >> Changes in v4 -> v5:
>> >> >> >> >> * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
>> >> >> >> >> * Rename *gcc_retain* to *gnu_retain*
>> >> >> >> >> ---
>> >> >> >> >>  config.h.in            |  3 +++
>> >> >> >> >>  configure              | 59 ++++++++++++++++++++++++++++++++++++++++++
>> >> >> >> >>  configure.ac           | 21 +++++++++++++++
>> >> >> >> >>  include/libc-symbols.h | 14 +++++++---
>> >> >> >> >>  libio/Makefile         | 32 +++++++++++++++++++++++
>> >> >> >> >>  libio/tst-cleanup.c    | 33 +++++++++++++++++++++++
>> >> >> >> >>  libio/tst-cleanup.exp  |  1 +
>> >> >> >> >>  7 files changed, 159 insertions(+), 4 deletions(-)
>> >> >> >> >>  create mode 100644 libio/tst-cleanup.c
>> >> >> >> >>  create mode 100644 libio/tst-cleanup.exp
>> >> >> >> >>
>> >> >> >> >> diff --git a/config.h.in b/config.h.in
>> >> >> >> >> index ca1547ae67..96a08c7757 100644
>> >> >> >> >> --- a/config.h.in
>> >> >> >> >> +++ b/config.h.in
>> >> >> >> >> @@ -187,6 +187,9 @@
>> >> >> >> >>  /* Define if gcc supports attribute ifunc.  */
>> >> >> >> >>  #undef HAVE_GCC_IFUNC
>> >> >> >> >>
>> >> >> >> >> +/* Define if CC supports attribute retain.  */
>> >> >> >> >> +#undef HAVE_GNU_RETAIN
>> >> >> >> >> +
>> >> >> >> >>  /* Define if the linker defines __ehdr_start.  */
>> >> >> >> >>  #undef HAVE_EHDR_START
>> >> >> >> >>
>> >> >> >> >> diff --git a/configure b/configure
>> >> >> >> >> index fcf43bf7de..e64b7f8efe 100755
>> >> >> >> >> --- a/configure
>> >> >> >> >> +++ b/configure
>> >> >> >> >> @@ -4105,6 +4105,31 @@ fi
>> >> >> >> >>  $as_echo "$libc_cv_textrel_ifunc" >&6; }
>> >> >> >> >>
>> >> >> >> >>
>> >> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
>> >> >> >> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
>> >> >> >> >> +if ${libc_cv_gnu_retain+:} false; then :
>> >> >> >> >> +  $as_echo_n "(cached) " >&6
>> >> >> >> >> +else
>> >> >> >> >> +  cat > conftest.c <<EOF
>> >> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> >> >> >> +EOF
>> >> >> >> >> +libc_cv_gnu_retain=no
>> >> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
>> >> >> >> >> +   2>&5 ; then
>> >> >> >> >> +  libc_cv_gnu_retain=yes
>> >> >> >> >> +fi
>> >> >> >> >> +rm -f conftest*
>> >> >> >> >> +fi
>> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
>> >> >> >> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
>> >> >> >> >> +if test $libc_cv_gnu_retain = yes; then
>> >> >> >> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
>> >> >> >> >> +
>> >> >> >> >> +fi
>> >> >> >> >> +config_vars="$config_vars
>> >> >> >> >> +have-gnu-retain = $libc_cv_gnu_retain"
>> >> >> >> >> +
>> >> >> >> >>  # Check if gcc warns about alias for function with incompatible types.
>> >> >> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
>> >> >> >> >>  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
>> >> >> >> >> @@ -5871,6 +5896,40 @@ fi
>> >> >> >> >>  $as_echo "$libc_linker_feature" >&6; }
>> >> >> >> >>
>> >> >> >> >>
>> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
>> >> >> >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
>> >> >> >> >> +libc_linker_feature=no
>> >> >> >> >> +if test x"$gnu_ld" = x"yes"; then
>> >> >> >> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
>> >> >> >> >> +  if test -n "$libc_linker_check"; then
>> >> >> >> >> +    cat > conftest.c <<EOF
>> >> >> >> >> +int _start (void) { return 42; }
>> >> >> >> >> +EOF
>> >> >> >> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
>> >> >> >> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
>> >> >> >> >> +                               -fPIC -shared -o conftest.so conftest.c
>> >> >> >> >> +                               1>&5'
>> >> >> >> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
>> >> >> >> >> +  (eval $ac_try) 2>&5
>> >> >> >> >> +  ac_status=$?
>> >> >> >> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
>> >> >> >> >> +  test $ac_status = 0; }; }
>> >> >> >> >> +    then
>> >> >> >> >> +      libc_linker_feature=yes
>> >> >> >> >> +    fi
>> >> >> >> >> +    rm -f conftest*
>> >> >> >> >> +  fi
>> >> >> >> >> +fi
>> >> >> >> >> +if test $libc_linker_feature = yes; then
>> >> >> >> >> +  libc_cv_z_start_stop_gc=yes
>> >> >> >> >> +else
>> >> >> >> >> +  libc_cv_z_start_stop_gc=no
>> >> >> >> >> +fi
>> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
>> >> >> >> >> +$as_echo "$libc_linker_feature" >&6; }
>> >> >> >> >> +config_vars="$config_vars
>> >> >> >> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
>> >> >> >> >> +
>> >> >> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>> >> >> >> >>  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>> >> >> >> >>  libc_linker_feature=no
>> >> >> >> >> diff --git a/configure.ac b/configure.ac
>> >> >> >> >> index fce967f2c2..cc47e56e82 100644
>> >> >> >> >> --- a/configure.ac
>> >> >> >> >> +++ b/configure.ac
>> >> >> >> >> @@ -707,6 +707,23 @@ fi
>> >> >> >> >>  rm -f conftest*])
>> >> >> >> >>  AC_SUBST(libc_cv_textrel_ifunc)
>> >> >> >> >>
>> >> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> >> >> >> +AC_CACHE_CHECK([for GNU attribute retain support],
>> >> >> >> >> +              libc_cv_gnu_retain, [dnl
>> >> >> >> >> +cat > conftest.c <<EOF
>> >> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> >> >> >> +EOF
>> >> >> >> >> +libc_cv_gnu_retain=no
>> >> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
>> >> >> >> >> +   2>&AS_MESSAGE_LOG_FD ; then
>> >> >> >> >> +  libc_cv_gnu_retain=yes
>> >> >> >> >> +fi
>> >> >> >> >> +rm -f conftest*])
>> >> >> >> >> +if test $libc_cv_gnu_retain = yes; then
>> >> >> >> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
>> >> >> >> >> +fi
>> >> >> >> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
>> >> >> >> >> +
>> >> >> >> >>  # Check if gcc warns about alias for function with incompatible types.
>> >> >> >> >>  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>> >> >> >> >>                libc_cv_gcc_incompatible_alias, [dnl
>> >> >> >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>> >> >> >> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>> >> >> >> >>  AC_SUBST(libc_cv_z_execstack)
>> >> >> >> >>
>> >> >> >> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
>> >> >> >> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
>> >> >> >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
>> >> >> >> >> +
>> >> >> >> >>  LIBC_LINKER_FEATURE([--no-dynamic-linker],
>> >> >> >> >>                     [-Wl,--no-dynamic-linker],
>> >> >> >> >>                     [libc_cv_no_dynamic_linker=yes],
>> >> >> >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
>> >> >> >> >> index 546fc26a7b..127ea656c2 100644
>> >> >> >> >> --- a/include/libc-symbols.h
>> >> >> >> >> +++ b/include/libc-symbols.h
>> >> >> >> >> @@ -352,6 +352,12 @@ for linking")
>> >> >> >> >>
>> >> >> >> >>  */
>> >> >> >> >>
>> >> >> >> >> +#ifdef HAVE_GNU_RETAIN
>> >> >> >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
>> >> >> >> >> +#else
>> >> >> >> >> +# define attribute_used_retain __attribute__ ((__used__))
>> >> >> >> >> +#endif
>> >> >> >> >> +
>> >> >> >> >>  /* Symbol set support macros.  */
>> >> >> >> >>
>> >> >> >> >>  /* Make SYMBOL, which is in the text segment, an element of SET.  */
>> >> >> >> >> @@ -367,12 +373,12 @@ for linking")
>> >> >> >> >>  /* When building a shared library, make the set section writable,
>> >> >> >> >>     because it will need to be relocated at run time anyway.  */
>> >> >> >> >>  # define _elf_set_element(set, symbol) \
>> >> >> >> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
>> >> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> >> >> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
>> >> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >> >> >> >>  #else
>> >> >> >> >>  # define _elf_set_element(set, symbol) \
>> >> >> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> >> >> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >> >> >> >>  #endif
>> >> >> >> >>
>> >> >> >> >>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
>> >> >> >> >> diff --git a/libio/Makefile b/libio/Makefile
>> >> >> >> >> index 12ce41038f..c9c232ebc2 100644
>> >> >> >> >> --- a/libio/Makefile
>> >> >> >> >> +++ b/libio/Makefile
>> >> >> >> >> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared))
>> >> >> >> >>  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>> >> >> >> >>                  $(objpfx)tst-bz24228-mem.out
>> >> >> >> >>  endif
>> >> >> >> >> +
>> >> >> >> >> +tests += tst-cleanup-default
>> >> >> >> >> +tests-static += tst-cleanup-default
>> >> >> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out
>> >> >> >> >
>> >> >> >> >Please make 2 tests,  tst-cleanup-default and tst-cleanup-default-static.
>> >> >> >>
>> >> >> >> Added.
>> >> >> >>
>> >> >> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> >> >> >> >> +
>> >> >> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> >> >> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
>> >> >> >> >> +tests-static += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
>> >> >> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> >> >> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
>> >> >> >> >
>> >> >> >> >Same here.
>> >> >> >>
>> >> >> >> Added.
>> >> >> >>
>> >> >> >> >> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
>> >> >> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc
>> >> >> >> >> +endif
>> >> >> >> >>  endif
>> >> >> >> >>
>> >> >> >> >>  include ../Rules
>> >> >> >> >> @@ -224,6 +238,24 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>> >> >> >> >>  $(objpfx)tst-wfile-sync.out: $(gen-locales)
>> >> >> >> >>  endif
>> >> >> >> >>
>> >> >> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> >> >> >> >> +       cmp $^ > $@; \
>> >> >> >> >> +       $(evaluate-test)
>> >> >> >> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
>> >> >> >> >> +       $(compile.c) -o $@
>> >> >> >> >> +
>> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> >> >> >> >> +       cmp $^ > $@; \
>> >> >> >> >> +       $(evaluate-test)
>> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> >> >> >> >> +       $(compile.c) -o $@
>> >> >> >> >> +
>> >> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
>> >> >> >> >> +       cmp $^ > $@; \
>> >> >> >> >> +       $(evaluate-test)
>> >> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
>> >> >> >> >> +       $(compile.c) -o $@
>> >> >> >> >>
>> >> >> >> >>  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>> >> >> >> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>> >> >> >> >>         $(common-objpfx)libio/; \
>> >> >> >> >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
>> >> >> >> >> new file mode 100644
>> >> >> >> >> index 0000000000..7f0a34a91e
>> >> >> >> >> --- /dev/null
>> >> >> >> >> +++ b/libio/tst-cleanup.c
>> >> >> >> >> @@ -0,0 +1,33 @@
>> >> >> >> >
>> >> >> >> >Please add a comment saying that test --gc-sections.
>> >> >> >>
>> >> >> >> OK, added.
>> >> >> >>
>> >> >> >> >> +/* Copyright (C) 2021 Free Software Foundation, Inc.
>> >> >> >> >> +   This file is part of the GNU C Library.
>> >> >> >> >> +
>> >> >> >> >> +   The GNU C Library is free software; you can redistribute it and/or
>> >> >> >> >> +   modify it under the terms of the GNU Lesser General Public
>> >> >> >> >> +   License as published by the Free Software Foundation; either
>> >> >> >> >> +   version 2.1 of the License, or (at your option) any later version.
>> >> >> >> >> +
>> >> >> >> >> +   The GNU C Library is distributed in the hope that it will be useful,
>> >> >> >> >> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>> >> >> >> >> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> >> >> >> >> +   Lesser General Public License for more details.
>> >> >> >> >> +
>> >> >> >> >> +   You should have received a copy of the GNU Lesser General Public
>> >> >> >> >> +   License along with the GNU C Library; if not, see
>> >> >> >> >> +   <https://www.gnu.org/licenses/>.  */
>> >> >> >> >> +
>> >> >> >> >> +/* Test that stdout is flushed after atexit callbacks were run.  */
>> >> >> >> >> +
>> >> >> >> >> +#include <stdio.h>
>> >> >> >> >> +#include <stdlib.h>
>> >> >> >> >> +
>> >> >> >> >> +void
>> >> >> >> >> +hook (void)
>> >> >> >> >> +{
>> >> >> >> >> +  puts ("hello");
>> >> >> >> >> +}
>> >> >> >> >> +
>> >> >> >> >> +int
>> >> >> >> >> +main (void)
>> >> >> >> >> +{
>> >> >> >> >> +  atexit (hook);
>> >> >> >> >> +}
>> >> >> >> >> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
>> >> >> >> >> new file mode 100644
>> >> >> >> >> index 0000000000..ce01362503
>> >> >> >> >> --- /dev/null
>> >> >> >> >> +++ b/libio/tst-cleanup.exp
>> >> >> >> >> @@ -0,0 +1 @@
>> >> >> >> >> +hello
>> >> >> >> >> --
>> >> >> >> >> 2.31.0.291.g576ba9dcdaf-goog
>> >> >> >> >>
>> >> >> >> >
>> >> >> >>
>> >> >> >> diff --git a/config.h.in b/config.h.in
>> >> >> >> index ca1547ae67..96a08c7757 100644
>> >> >> >> --- a/config.h.in
>> >> >> >> +++ b/config.h.in
>> >> >> >> @@ -187,6 +187,9 @@
>> >> >> >>   /* Define if gcc supports attribute ifunc.  */
>> >> >> >>   #undef HAVE_GCC_IFUNC
>> >> >> >>
>> >> >> >> +/* Define if CC supports attribute retain.  */
>> >> >> >> +#undef HAVE_GNU_RETAIN
>> >> >> >> +
>> >> >> >>   /* Define if the linker defines __ehdr_start.  */
>> >> >> >>   #undef HAVE_EHDR_START
>> >> >> >>
>> >> >> >> diff --git a/configure b/configure
>> >> >> >> index fcf43bf7de..e64b7f8efe 100755
>> >> >> >> --- a/configure
>> >> >> >> +++ b/configure
>> >> >> >> @@ -4105,6 +4105,31 @@ fi
>> >> >> >>   $as_echo "$libc_cv_textrel_ifunc" >&6; }
>> >> >> >>
>> >> >> >>
>> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
>> >> >> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
>> >> >> >> +if ${libc_cv_gnu_retain+:} false; then :
>> >> >> >> +  $as_echo_n "(cached) " >&6
>> >> >> >> +else
>> >> >> >> +  cat > conftest.c <<EOF
>> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> >> >> +EOF
>> >> >> >> +libc_cv_gnu_retain=no
>> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
>> >> >> >> +   2>&5 ; then
>> >> >> >> +  libc_cv_gnu_retain=yes
>> >> >> >> +fi
>> >> >> >> +rm -f conftest*
>> >> >> >> +fi
>> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
>> >> >> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
>> >> >> >> +if test $libc_cv_gnu_retain = yes; then
>> >> >> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
>> >> >> >> +
>> >> >> >> +fi
>> >> >> >> +config_vars="$config_vars
>> >> >> >> +have-gnu-retain = $libc_cv_gnu_retain"
>> >> >> >> +
>> >> >> >>   # Check if gcc warns about alias for function with incompatible types.
>> >> >> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
>> >> >> >>   $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
>> >> >> >> @@ -5871,6 +5896,40 @@ fi
>> >> >> >>   $as_echo "$libc_linker_feature" >&6; }
>> >> >> >>
>> >> >> >>
>> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
>> >> >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
>> >> >> >> +libc_linker_feature=no
>> >> >> >> +if test x"$gnu_ld" = x"yes"; then
>> >> >> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
>> >> >> >> +  if test -n "$libc_linker_check"; then
>> >> >> >> +    cat > conftest.c <<EOF
>> >> >> >> +int _start (void) { return 42; }
>> >> >> >> +EOF
>> >> >> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
>> >> >> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
>> >> >> >> +                               -fPIC -shared -o conftest.so conftest.c
>> >> >> >> +                               1>&5'
>> >> >> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
>> >> >> >> +  (eval $ac_try) 2>&5
>> >> >> >> +  ac_status=$?
>> >> >> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
>> >> >> >> +  test $ac_status = 0; }; }
>> >> >> >> +    then
>> >> >> >> +      libc_linker_feature=yes
>> >> >> >> +    fi
>> >> >> >> +    rm -f conftest*
>> >> >> >> +  fi
>> >> >> >> +fi
>> >> >> >> +if test $libc_linker_feature = yes; then
>> >> >> >> +  libc_cv_z_start_stop_gc=yes
>> >> >> >> +else
>> >> >> >> +  libc_cv_z_start_stop_gc=no
>> >> >> >> +fi
>> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
>> >> >> >> +$as_echo "$libc_linker_feature" >&6; }
>> >> >> >> +config_vars="$config_vars
>> >> >> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
>> >> >> >> +
>> >> >> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>> >> >> >>   $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>> >> >> >>   libc_linker_feature=no
>> >> >> >> diff --git a/configure.ac b/configure.ac
>> >> >> >> index fce967f2c2..cc47e56e82 100644
>> >> >> >> --- a/configure.ac
>> >> >> >> +++ b/configure.ac
>> >> >> >> @@ -707,6 +707,23 @@ fi
>> >> >> >>   rm -f conftest*])
>> >> >> >>   AC_SUBST(libc_cv_textrel_ifunc)
>> >> >> >>
>> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> >> >> +AC_CACHE_CHECK([for GNU attribute retain support],
>> >> >> >> +              libc_cv_gnu_retain, [dnl
>> >> >> >> +cat > conftest.c <<EOF
>> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> >> >> +EOF
>> >> >> >> +libc_cv_gnu_retain=no
>> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
>> >> >> >> +   2>&AS_MESSAGE_LOG_FD ; then
>> >> >> >> +  libc_cv_gnu_retain=yes
>> >> >> >> +fi
>> >> >> >> +rm -f conftest*])
>> >> >> >> +if test $libc_cv_gnu_retain = yes; then
>> >> >> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
>> >> >> >> +fi
>> >> >> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
>> >> >> >> +
>> >> >> >>   # Check if gcc warns about alias for function with incompatible types.
>> >> >> >>   AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>> >> >> >>                libc_cv_gcc_incompatible_alias, [dnl
>> >> >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>> >> >> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>> >> >> >>   AC_SUBST(libc_cv_z_execstack)
>> >> >> >>
>> >> >> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
>> >> >> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
>> >> >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
>> >> >> >> +
>> >> >> >>   LIBC_LINKER_FEATURE([--no-dynamic-linker],
>> >> >> >>                     [-Wl,--no-dynamic-linker],
>> >> >> >>                     [libc_cv_no_dynamic_linker=yes],
>> >> >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
>> >> >> >> index 546fc26a7b..127ea656c2 100644
>> >> >> >> --- a/include/libc-symbols.h
>> >> >> >> +++ b/include/libc-symbols.h
>> >> >> >> @@ -352,6 +352,12 @@ for linking")
>> >> >> >>
>> >> >> >>   */
>> >> >> >>
>> >> >> >> +#ifdef HAVE_GNU_RETAIN
>> >> >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
>> >> >> >> +#else
>> >> >> >> +# define attribute_used_retain __attribute__ ((__used__))
>> >> >> >> +#endif
>> >> >> >> +
>> >> >> >>   /* Symbol set support macros.  */
>> >> >> >>
>> >> >> >>   /* Make SYMBOL, which is in the text segment, an element of SET.  */
>> >> >> >> @@ -367,12 +373,12 @@ for linking")
>> >> >> >>   /* When building a shared library, make the set section writable,
>> >> >> >>      because it will need to be relocated at run time anyway.  */
>> >> >> >>   # define _elf_set_element(set, symbol) \
>> >> >> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
>> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> >> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
>> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >> >> >>   #else
>> >> >> >>   # define _elf_set_element(set, symbol) \
>> >> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> >> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >> >> >>   #endif
>> >> >> >>
>> >> >> >>   /* Define SET as a symbol set.  This may be required (it is in a.out) to
>> >> >> >> diff --git a/libio/Makefile b/libio/Makefile
>> >> >> >> index 12ce41038f..ad0d53bb49 100644
>> >> >> >> --- a/libio/Makefile
>> >> >> >> +++ b/libio/Makefile
>> >> >> >> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
>> >> >> >>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>> >> >> >>                  $(objpfx)tst-bz24228-mem.out
>> >> >> >>   endif
>> >> >> >> +
>> >> >> >> +tests += tst-cleanup-default tst-cleanup-default-static
>> >> >> >> +tests-static += tst-cleanup-default-static
>> >> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
>> >> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> >> >> >> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
>> >> >> >> +
>> >> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> >> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
>> >> >> >> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
>> >> >> >> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
>> >> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> >> >> >> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
>> >> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
>> >> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
>> >> >> >> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
>> >> >> >> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
>> >> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
>> >> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
>> >> >> >> +endif
>> >> >> >>   endif
>> >> >> >>
>> >> >> >>   include ../Rules
>> >> >> >> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>> >> >> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>> >> >> >>   endif
>> >> >> >>
>> >> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> >> >> >> +       cmp $^ > $@; \
>> >> >> >> +       $(evaluate-test)
>> >> >> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
>> >> >> >> +       $(compile.c) -o $@
>> >> >> >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
>> >> >> >> +       cmp $^ > $@; \
>> >> >> >> +       $(evaluate-test)
>> >> >> >> +$(objpfx)tst-cleanup-default-static.o: tst-cleanup.c
>> >> >> >> +       $(compile.c) -o $@
>> >> >> >> +
>> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> >> >> >> +       cmp $^ > $@; \
>> >> >> >> +       $(evaluate-test)
>> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> >> >> >> +       $(compile.c) -o $@
>> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
>> >> >> >> +       cmp $^ > $@; \
>> >> >> >> +       $(evaluate-test)
>> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c
>> >> >> >> +       $(compile.c) -o $@
>> >> >> >
>> >> >> >Please add a separate .c file for each test to get the correct dependency.
>> >> >>
>> >> >> Changed this block to:
>> >> >>
>> >> >> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>> >> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>> >> >>   endif
>> >> >>
>> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> >> >> +       cmp $^ > $@; \
>> >> >> +       $(evaluate-test)
>> >> >> +$(objpfx)tst-cleanup-default.c: tst-cleanup.c
>> >> >> +       cp $< $@
>> >> >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
>> >> >> +       cmp $^ > $@; \
>> >> >> +       $(evaluate-test)
>> >> >> +$(objpfx)tst-cleanup-default-static.c: tst-cleanup.c
>> >> >> +       cp $< $@
>> >> >> +
>> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> >> >> +       cmp $^ > $@; \
>> >> >> +       $(evaluate-test)
>> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> >> >> +       $(compile.c) -o $@
>> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
>> >> >> +       cmp $^ > $@; \
>> >> >> +       $(evaluate-test)
>> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static.c: tst-cleanup.c
>> >> >> +       cp $< $@
>> >> >> +
>> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
>> >> >> +       cmp $^ > $@; \
>> >> >> +       $(evaluate-test)
>> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc.c: tst-cleanup.c
>> >> >> +       cp $< $@
>> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc-static.out
>> >> >> +       cmp $^ > $@; \
>> >> >> +       $(evaluate-test)
>> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-static.c: tst-cleanup.c
>> >> >> +       cp $< $@
>> >> >> +
>> >> >>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>> >> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>> >> >>         $(common-objpfx)libio/; \
>> >> >>
>> >> >
>> >> >"make clean" doesn't remove the generated files. The standard way in glibc
>> >> >is to add a *-static.c source.
>> >>
>> >> I'll use .INTERMEDIATE and $(eval $(call ..))
>> >>
>> >> diff --git a/libio/Makefile b/libio/Makefile
>> >> index 12ce41038f..a9b44f04df 100644
>> >> --- a/libio/Makefile
>> >> +++ b/libio/Makefile
>> >> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
>> >>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>> >>                  $(objpfx)tst-bz24228-mem.out
>> >>   endif
>> >> +
>> >> +tests += tst-cleanup-default tst-cleanup-default-static
>> >> +tests-static += tst-cleanup-default-static
>> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
>> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> >> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
>> >> +
>> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
>> >> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
>> >> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
>> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> >> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
>> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
>> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
>> >> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
>> >> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
>> >> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
>> >> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
>> >> +endif
>> >>   endif
>> >>
>> >>   include ../Rules
>> >> @@ -224,6 +244,17 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>> >>   endif
>> >>
>> >> +define gen-tst-cleanup
>> >> +$(objpfx)tst-cleanup-$1-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-$1.out
>> >> +       cmp $$^ > $$@; $$(evaluate-test)
>> >> +$(objpfx)tst-cleanup-$1.c: tst-cleanup.c
>> >> +       cp $$< $$@
>> >> +.INTERMEDIATE: $(objpfx)tst-cleanup-$1.c
>> >> +endef
>> >> +
>> >> +$(foreach t, default default-static start-stop-gc start-stop-gc-static nostart-stop-gc nostart-stop-gc-static, \
>> >> +  $(eval $(call gen-tst-cleanup,$(t))))
>> >> +
>> >>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>> >>         $(common-objpfx)libio/; \
>> >
>> >There are 2 issues with static tests:
>> >
>> >1. A separate static source is needed.
>>
>> .INTERMEDIATE perfectly solves the lingering copied source issue.
>> I don't see lingering libio/tst-cleanup-*.c
>
>I was referring to
>
>elf/tst-array1-static.c
>elf/tst-array5-static.c
>elf/tst-dl-iter-static.c
>elf/tst-dst-static.c
>elf/tst-leaks1-static.c
>elf/tst-libc_dlvsym-static.c
>elf/tst-linkall-static.c
>elf/tst-ptrguard1-static.c
>elf/tst-single_threaded-pthread-static.c
>elf/tst-single_threaded-static.c
>elf/tst-stackguard1-static.c
>elf/tst-tls1-static.c
>elf/tst-tls2-static.c
>elf/tst-tls9-static.c
>elf/tst-tlsalign-extern-static.c
>elf/tst-tlsalign-static.c
>gmon/tst-gmon-static.c
>gmon/tst-profile-static.c
>localedata/bug-setlocale1-static.c
>localedata/tst-langinfo-newlocale-static.c
>localedata/tst-langinfo-setlocale-static.c
>localedata/tst-langinfo-static.c
>malloc/tst-malloc-usable-static.c
>math/test-fpucw-ieee-static.c
>math/test-fpucw-static.c
>math/test-signgam-uchar-init-static.c
>math/test-signgam-uchar-static.c
>math/test-signgam-uint-init-static.c
>math/test-signgam-uint-static.c
>math/test-signgam-ullong-init-static.c
>math/test-signgam-ullong-static.c
>nptl/tst-mutex8-static.c
>nptl/tst-mutexpi8-static.c
>nptl/tst-sem11-static.c
>nptl/tst-sem12-static.c
>nptl/tst-setuid1-static.c
>nptl/tst-stackguard1-static.c
>nss/tst-nss-static.c
>posix/tst-exec-static.c
>posix/tst-spawn-static.c
>setjmp/tst-setjmp-static.c
>
>> >2. We need to add the static test to both tests and tests-static.
>>
>> tests-static suffices. I have checked some tests-static usage in other
>> directories.
>
>There are
>
>tests           := tst-setjmp jmpbug bug269-setjmp tst-setjmp-fp \
>                   tst-sigsetjmp tst-setjmp-static
>tests-static    := tst-setjmp-static
>
>They should be replaced by something like
>
>tests           := tst-setjmp jmpbug bug269-setjmp tst-setjmp-fp \
>                   tst-sigsetjmp
>tests-static-add := tst-setjmp-static

Re-checking, the tst-cleanup* targets are in tests-special so `make tests` will build them.
If a tests-static target is not in tests-internal/tests-special, looks like it needs to be in tests.

As is, I think my usage is correct.

>> I have additionally checked that:
>>
>> * touch libc.a => next invocation `make -r -C ~/Dev/glibc/libio objdir=$PWD check -j 20` will rebuild the static tests
>> * touch libc.so => next invocation `make -r -C ~/Dev/glibc/libio objdir=$PWD check -j 20` will rebuild the dynamic tests
>> * rm libio/tst-cleanup-default-cmp.out => next invocation `make -r -C ~/Dev/glibc/libio objdir=$PWD check -j 20` will rerun the single test
>>
>> >If you want to add a separate static source, you can submit a separate patch
>> >to address these 2 issues together.
  

On Mon, Apr 5, 2021 at 2:03 PM Fangrui Song <maskray@google.com> wrote:
>
> On 2021-04-05, H.J. Lu wrote:
> >On Mon, Apr 5, 2021 at 11:17 AM Fangrui Song <maskray@google.com> wrote:
> >>
> >> On 2021-04-04, H.J. Lu wrote:
> >> >On Sat, Apr 3, 2021 at 2:57 PM Fangrui Song <maskray@google.com> wrote:
> >> >>
> >> >> On 2021-04-03, H.J. Lu wrote:
> >> >> >On Sat, Apr 3, 2021 at 11:02 AM Fangrui Song <maskray@google.com> wrote:
> >> >> >>
> >> >> >>
> >> >> >> On 2021-04-02, H.J. Lu wrote:
> >> >> >> >On Thu, Apr 1, 2021 at 8:23 PM Fangrui Song <maskray@google.com> wrote:
> >> >> >> >>
> >> >> >> >> On 2021-04-01, H.J. Lu wrote:
> >> >> >> >> >On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song <maskray@google.com> wrote:
> >> >> >> >> >>
> >> >> >> >> >> So that text_set_element/data_set_element/bss_set_element defined
> >> >> >> >> >> variables will be retained by the linker.
> >> >> >> >> >>
> >> >> >> >> >> Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
> >> >> >> >> >> will not be optimized out; 'retain' prevents section garbage collection
> >> >> >> >> >> if the linker support SHF_GNU_RETAIN.
> >> >> >> >> >>
> >> >> >> >> >> GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
> >> >> >> >> >> identifier name sections to be GCed even if there are live
> >> >> >> >> >> __start_/__stop_ references.
> >> >> >> >> >>
> >> >> >> >> >> Without the change, there are some static linking problems, e.g.
> >> >> >> >> >> _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
> >> >> >> >> >> stdout is not flushed on exit.
> >> >> >> >> >>
> >> >> >> >> >> Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
> >> >> >> >> >> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
> >> >> >> >> >> ---
> >> >> >> >> >> Changes in v1 -> v2:
> >> >> >> >> >> * Define attribute_used_retain_section
> >> >> >> >> >> Changes in v2 -> v3:
> >> >> >> >> >> * Use attribute_used_retain instead attribute_used_retain_section
> >> >> >> >> >> Changes in v3 -> v4:
> >> >> >> >> >> * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
> >> >> >> >> >> Changes in v4 -> v5:
> >> >> >> >> >> * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
> >> >> >> >> >> * Rename *gcc_retain* to *gnu_retain*
> >> >> >> >> >> ---
> >> >> >> >> >>  config.h.in            |  3 +++
> >> >> >> >> >>  configure              | 59 ++++++++++++++++++++++++++++++++++++++++++
> >> >> >> >> >>  configure.ac           | 21 +++++++++++++++
> >> >> >> >> >>  include/libc-symbols.h | 14 +++++++---
> >> >> >> >> >>  libio/Makefile         | 32 +++++++++++++++++++++++
> >> >> >> >> >>  libio/tst-cleanup.c    | 33 +++++++++++++++++++++++
> >> >> >> >> >>  libio/tst-cleanup.exp  |  1 +
> >> >> >> >> >>  7 files changed, 159 insertions(+), 4 deletions(-)
> >> >> >> >> >>  create mode 100644 libio/tst-cleanup.c
> >> >> >> >> >>  create mode 100644 libio/tst-cleanup.exp
> >> >> >> >> >>
> >> >> >> >> >> diff --git a/config.h.in b/config.h.in
> >> >> >> >> >> index ca1547ae67..96a08c7757 100644
> >> >> >> >> >> --- a/config.h.in
> >> >> >> >> >> +++ b/config.h.in
> >> >> >> >> >> @@ -187,6 +187,9 @@
> >> >> >> >> >>  /* Define if gcc supports attribute ifunc.  */
> >> >> >> >> >>  #undef HAVE_GCC_IFUNC
> >> >> >> >> >>
> >> >> >> >> >> +/* Define if CC supports attribute retain.  */
> >> >> >> >> >> +#undef HAVE_GNU_RETAIN
> >> >> >> >> >> +
> >> >> >> >> >>  /* Define if the linker defines __ehdr_start.  */
> >> >> >> >> >>  #undef HAVE_EHDR_START
> >> >> >> >> >>
> >> >> >> >> >> diff --git a/configure b/configure
> >> >> >> >> >> index fcf43bf7de..e64b7f8efe 100755
> >> >> >> >> >> --- a/configure
> >> >> >> >> >> +++ b/configure
> >> >> >> >> >> @@ -4105,6 +4105,31 @@ fi
> >> >> >> >> >>  $as_echo "$libc_cv_textrel_ifunc" >&6; }
> >> >> >> >> >>
> >> >> >> >> >>
> >> >> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
> >> >> >> >> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
> >> >> >> >> >> +if ${libc_cv_gnu_retain+:} false; then :
> >> >> >> >> >> +  $as_echo_n "(cached) " >&6
> >> >> >> >> >> +else
> >> >> >> >> >> +  cat > conftest.c <<EOF
> >> >> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> >> >> >> +EOF
> >> >> >> >> >> +libc_cv_gnu_retain=no
> >> >> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> >> >> >> >> >> +   2>&5 ; then
> >> >> >> >> >> +  libc_cv_gnu_retain=yes
> >> >> >> >> >> +fi
> >> >> >> >> >> +rm -f conftest*
> >> >> >> >> >> +fi
> >> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
> >> >> >> >> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
> >> >> >> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> >> >> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
> >> >> >> >> >> +
> >> >> >> >> >> +fi
> >> >> >> >> >> +config_vars="$config_vars
> >> >> >> >> >> +have-gnu-retain = $libc_cv_gnu_retain"
> >> >> >> >> >> +
> >> >> >> >> >>  # Check if gcc warns about alias for function with incompatible types.
> >> >> >> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
> >> >> >> >> >>  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
> >> >> >> >> >> @@ -5871,6 +5896,40 @@ fi
> >> >> >> >> >>  $as_echo "$libc_linker_feature" >&6; }
> >> >> >> >> >>
> >> >> >> >> >>
> >> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
> >> >> >> >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
> >> >> >> >> >> +libc_linker_feature=no
> >> >> >> >> >> +if test x"$gnu_ld" = x"yes"; then
> >> >> >> >> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
> >> >> >> >> >> +  if test -n "$libc_linker_check"; then
> >> >> >> >> >> +    cat > conftest.c <<EOF
> >> >> >> >> >> +int _start (void) { return 42; }
> >> >> >> >> >> +EOF
> >> >> >> >> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> >> >> >> >> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
> >> >> >> >> >> +                               -fPIC -shared -o conftest.so conftest.c
> >> >> >> >> >> +                               1>&5'
> >> >> >> >> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> >> >> >> >> >> +  (eval $ac_try) 2>&5
> >> >> >> >> >> +  ac_status=$?
> >> >> >> >> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> >> >> >> >> >> +  test $ac_status = 0; }; }
> >> >> >> >> >> +    then
> >> >> >> >> >> +      libc_linker_feature=yes
> >> >> >> >> >> +    fi
> >> >> >> >> >> +    rm -f conftest*
> >> >> >> >> >> +  fi
> >> >> >> >> >> +fi
> >> >> >> >> >> +if test $libc_linker_feature = yes; then
> >> >> >> >> >> +  libc_cv_z_start_stop_gc=yes
> >> >> >> >> >> +else
> >> >> >> >> >> +  libc_cv_z_start_stop_gc=no
> >> >> >> >> >> +fi
> >> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> >> >> >> >> >> +$as_echo "$libc_linker_feature" >&6; }
> >> >> >> >> >> +config_vars="$config_vars
> >> >> >> >> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
> >> >> >> >> >> +
> >> >> >> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
> >> >> >> >> >>  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
> >> >> >> >> >>  libc_linker_feature=no
> >> >> >> >> >> diff --git a/configure.ac b/configure.ac
> >> >> >> >> >> index fce967f2c2..cc47e56e82 100644
> >> >> >> >> >> --- a/configure.ac
> >> >> >> >> >> +++ b/configure.ac
> >> >> >> >> >> @@ -707,6 +707,23 @@ fi
> >> >> >> >> >>  rm -f conftest*])
> >> >> >> >> >>  AC_SUBST(libc_cv_textrel_ifunc)
> >> >> >> >> >>
> >> >> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> >> >> >> +AC_CACHE_CHECK([for GNU attribute retain support],
> >> >> >> >> >> +              libc_cv_gnu_retain, [dnl
> >> >> >> >> >> +cat > conftest.c <<EOF
> >> >> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> >> >> >> +EOF
> >> >> >> >> >> +libc_cv_gnu_retain=no
> >> >> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
> >> >> >> >> >> +   2>&AS_MESSAGE_LOG_FD ; then
> >> >> >> >> >> +  libc_cv_gnu_retain=yes
> >> >> >> >> >> +fi
> >> >> >> >> >> +rm -f conftest*])
> >> >> >> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> >> >> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
> >> >> >> >> >> +fi
> >> >> >> >> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
> >> >> >> >> >> +
> >> >> >> >> >>  # Check if gcc warns about alias for function with incompatible types.
> >> >> >> >> >>  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
> >> >> >> >> >>                libc_cv_gcc_incompatible_alias, [dnl
> >> >> >> >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
> >> >> >> >> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
> >> >> >> >> >>  AC_SUBST(libc_cv_z_execstack)
> >> >> >> >> >>
> >> >> >> >> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> >> >> >> >> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> >> >> >> >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
> >> >> >> >> >> +
> >> >> >> >> >>  LIBC_LINKER_FEATURE([--no-dynamic-linker],
> >> >> >> >> >>                     [-Wl,--no-dynamic-linker],
> >> >> >> >> >>                     [libc_cv_no_dynamic_linker=yes],
> >> >> >> >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
> >> >> >> >> >> index 546fc26a7b..127ea656c2 100644
> >> >> >> >> >> --- a/include/libc-symbols.h
> >> >> >> >> >> +++ b/include/libc-symbols.h
> >> >> >> >> >> @@ -352,6 +352,12 @@ for linking")
> >> >> >> >> >>
> >> >> >> >> >>  */
> >> >> >> >> >>
> >> >> >> >> >> +#ifdef HAVE_GNU_RETAIN
> >> >> >> >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
> >> >> >> >> >> +#else
> >> >> >> >> >> +# define attribute_used_retain __attribute__ ((__used__))
> >> >> >> >> >> +#endif
> >> >> >> >> >> +
> >> >> >> >> >>  /* Symbol set support macros.  */
> >> >> >> >> >>
> >> >> >> >> >>  /* Make SYMBOL, which is in the text segment, an element of SET.  */
> >> >> >> >> >> @@ -367,12 +373,12 @@ for linking")
> >> >> >> >> >>  /* When building a shared library, make the set section writable,
> >> >> >> >> >>     because it will need to be relocated at run time anyway.  */
> >> >> >> >> >>  # define _elf_set_element(set, symbol) \
> >> >> >> >> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> >> >> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >> >> >> >>  #else
> >> >> >> >> >>  # define _elf_set_element(set, symbol) \
> >> >> >> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> >> >> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >> >> >> >>  #endif
> >> >> >> >> >>
> >> >> >> >> >>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
> >> >> >> >> >> diff --git a/libio/Makefile b/libio/Makefile
> >> >> >> >> >> index 12ce41038f..c9c232ebc2 100644
> >> >> >> >> >> --- a/libio/Makefile
> >> >> >> >> >> +++ b/libio/Makefile
> >> >> >> >> >> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared))
> >> >> >> >> >>  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
> >> >> >> >> >>                  $(objpfx)tst-bz24228-mem.out
> >> >> >> >> >>  endif
> >> >> >> >> >> +
> >> >> >> >> >> +tests += tst-cleanup-default
> >> >> >> >> >> +tests-static += tst-cleanup-default
> >> >> >> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out
> >> >> >> >> >
> >> >> >> >> >Please make 2 tests,  tst-cleanup-default and tst-cleanup-default-static.
> >> >> >> >>
> >> >> >> >> Added.
> >> >> >> >>
> >> >> >> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> >> >> >> >> >> +
> >> >> >> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> >> >> >> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> >> >> >> >> >> +tests-static += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> >> >> >> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> >> >> >> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
> >> >> >> >> >
> >> >> >> >> >Same here.
> >> >> >> >>
> >> >> >> >> Added.
> >> >> >> >>
> >> >> >> >> >> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
> >> >> >> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc
> >> >> >> >> >> +endif
> >> >> >> >> >>  endif
> >> >> >> >> >>
> >> >> >> >> >>  include ../Rules
> >> >> >> >> >> @@ -224,6 +238,24 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >> >> >> >> >>  $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >> >> >> >> >>  endif
> >> >> >> >> >>
> >> >> >> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> >> >> >> >> >> +       cmp $^ > $@; \
> >> >> >> >> >> +       $(evaluate-test)
> >> >> >> >> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
> >> >> >> >> >> +       $(compile.c) -o $@
> >> >> >> >> >> +
> >> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> >> >> >> >> >> +       cmp $^ > $@; \
> >> >> >> >> >> +       $(evaluate-test)
> >> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> >> >> >> >> >> +       $(compile.c) -o $@
> >> >> >> >> >> +
> >> >> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
> >> >> >> >> >> +       cmp $^ > $@; \
> >> >> >> >> >> +       $(evaluate-test)
> >> >> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
> >> >> >> >> >> +       $(compile.c) -o $@
> >> >> >> >> >>
> >> >> >> >> >>  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
> >> >> >> >> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
> >> >> >> >> >>         $(common-objpfx)libio/; \
> >> >> >> >> >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
> >> >> >> >> >> new file mode 100644
> >> >> >> >> >> index 0000000000..7f0a34a91e
> >> >> >> >> >> --- /dev/null
> >> >> >> >> >> +++ b/libio/tst-cleanup.c
> >> >> >> >> >> @@ -0,0 +1,33 @@
> >> >> >> >> >
> >> >> >> >> >Please add a comment saying that test --gc-sections.
> >> >> >> >>
> >> >> >> >> OK, added.
> >> >> >> >>
> >> >> >> >> >> +/* Copyright (C) 2021 Free Software Foundation, Inc.
> >> >> >> >> >> +   This file is part of the GNU C Library.
> >> >> >> >> >> +
> >> >> >> >> >> +   The GNU C Library is free software; you can redistribute it and/or
> >> >> >> >> >> +   modify it under the terms of the GNU Lesser General Public
> >> >> >> >> >> +   License as published by the Free Software Foundation; either
> >> >> >> >> >> +   version 2.1 of the License, or (at your option) any later version.
> >> >> >> >> >> +
> >> >> >> >> >> +   The GNU C Library is distributed in the hope that it will be useful,
> >> >> >> >> >> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> >> >> >> >> >> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> >> >> >> >> >> +   Lesser General Public License for more details.
> >> >> >> >> >> +
> >> >> >> >> >> +   You should have received a copy of the GNU Lesser General Public
> >> >> >> >> >> +   License along with the GNU C Library; if not, see
> >> >> >> >> >> +   <https://www.gnu.org/licenses/>.  */
> >> >> >> >> >> +
> >> >> >> >> >> +/* Test that stdout is flushed after atexit callbacks were run.  */
> >> >> >> >> >> +
> >> >> >> >> >> +#include <stdio.h>
> >> >> >> >> >> +#include <stdlib.h>
> >> >> >> >> >> +
> >> >> >> >> >> +void
> >> >> >> >> >> +hook (void)
> >> >> >> >> >> +{
> >> >> >> >> >> +  puts ("hello");
> >> >> >> >> >> +}
> >> >> >> >> >> +
> >> >> >> >> >> +int
> >> >> >> >> >> +main (void)
> >> >> >> >> >> +{
> >> >> >> >> >> +  atexit (hook);
> >> >> >> >> >> +}
> >> >> >> >> >> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
> >> >> >> >> >> new file mode 100644
> >> >> >> >> >> index 0000000000..ce01362503
> >> >> >> >> >> --- /dev/null
> >> >> >> >> >> +++ b/libio/tst-cleanup.exp
> >> >> >> >> >> @@ -0,0 +1 @@
> >> >> >> >> >> +hello
> >> >> >> >> >> --
> >> >> >> >> >> 2.31.0.291.g576ba9dcdaf-goog
> >> >> >> >> >>
> >> >> >> >> >
> >> >> >> >>
> >> >> >> >> diff --git a/config.h.in b/config.h.in
> >> >> >> >> index ca1547ae67..96a08c7757 100644
> >> >> >> >> --- a/config.h.in
> >> >> >> >> +++ b/config.h.in
> >> >> >> >> @@ -187,6 +187,9 @@
> >> >> >> >>   /* Define if gcc supports attribute ifunc.  */
> >> >> >> >>   #undef HAVE_GCC_IFUNC
> >> >> >> >>
> >> >> >> >> +/* Define if CC supports attribute retain.  */
> >> >> >> >> +#undef HAVE_GNU_RETAIN
> >> >> >> >> +
> >> >> >> >>   /* Define if the linker defines __ehdr_start.  */
> >> >> >> >>   #undef HAVE_EHDR_START
> >> >> >> >>
> >> >> >> >> diff --git a/configure b/configure
> >> >> >> >> index fcf43bf7de..e64b7f8efe 100755
> >> >> >> >> --- a/configure
> >> >> >> >> +++ b/configure
> >> >> >> >> @@ -4105,6 +4105,31 @@ fi
> >> >> >> >>   $as_echo "$libc_cv_textrel_ifunc" >&6; }
> >> >> >> >>
> >> >> >> >>
> >> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
> >> >> >> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
> >> >> >> >> +if ${libc_cv_gnu_retain+:} false; then :
> >> >> >> >> +  $as_echo_n "(cached) " >&6
> >> >> >> >> +else
> >> >> >> >> +  cat > conftest.c <<EOF
> >> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> >> >> +EOF
> >> >> >> >> +libc_cv_gnu_retain=no
> >> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> >> >> >> >> +   2>&5 ; then
> >> >> >> >> +  libc_cv_gnu_retain=yes
> >> >> >> >> +fi
> >> >> >> >> +rm -f conftest*
> >> >> >> >> +fi
> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
> >> >> >> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
> >> >> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> >> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
> >> >> >> >> +
> >> >> >> >> +fi
> >> >> >> >> +config_vars="$config_vars
> >> >> >> >> +have-gnu-retain = $libc_cv_gnu_retain"
> >> >> >> >> +
> >> >> >> >>   # Check if gcc warns about alias for function with incompatible types.
> >> >> >> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
> >> >> >> >>   $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
> >> >> >> >> @@ -5871,6 +5896,40 @@ fi
> >> >> >> >>   $as_echo "$libc_linker_feature" >&6; }
> >> >> >> >>
> >> >> >> >>
> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
> >> >> >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
> >> >> >> >> +libc_linker_feature=no
> >> >> >> >> +if test x"$gnu_ld" = x"yes"; then
> >> >> >> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
> >> >> >> >> +  if test -n "$libc_linker_check"; then
> >> >> >> >> +    cat > conftest.c <<EOF
> >> >> >> >> +int _start (void) { return 42; }
> >> >> >> >> +EOF
> >> >> >> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> >> >> >> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
> >> >> >> >> +                               -fPIC -shared -o conftest.so conftest.c
> >> >> >> >> +                               1>&5'
> >> >> >> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> >> >> >> >> +  (eval $ac_try) 2>&5
> >> >> >> >> +  ac_status=$?
> >> >> >> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> >> >> >> >> +  test $ac_status = 0; }; }
> >> >> >> >> +    then
> >> >> >> >> +      libc_linker_feature=yes
> >> >> >> >> +    fi
> >> >> >> >> +    rm -f conftest*
> >> >> >> >> +  fi
> >> >> >> >> +fi
> >> >> >> >> +if test $libc_linker_feature = yes; then
> >> >> >> >> +  libc_cv_z_start_stop_gc=yes
> >> >> >> >> +else
> >> >> >> >> +  libc_cv_z_start_stop_gc=no
> >> >> >> >> +fi
> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> >> >> >> >> +$as_echo "$libc_linker_feature" >&6; }
> >> >> >> >> +config_vars="$config_vars
> >> >> >> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
> >> >> >> >> +
> >> >> >> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
> >> >> >> >>   $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
> >> >> >> >>   libc_linker_feature=no
> >> >> >> >> diff --git a/configure.ac b/configure.ac
> >> >> >> >> index fce967f2c2..cc47e56e82 100644
> >> >> >> >> --- a/configure.ac
> >> >> >> >> +++ b/configure.ac
> >> >> >> >> @@ -707,6 +707,23 @@ fi
> >> >> >> >>   rm -f conftest*])
> >> >> >> >>   AC_SUBST(libc_cv_textrel_ifunc)
> >> >> >> >>
> >> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> >> >> >> >> +AC_CACHE_CHECK([for GNU attribute retain support],
> >> >> >> >> +              libc_cv_gnu_retain, [dnl
> >> >> >> >> +cat > conftest.c <<EOF
> >> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
> >> >> >> >> +EOF
> >> >> >> >> +libc_cv_gnu_retain=no
> >> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
> >> >> >> >> +   2>&AS_MESSAGE_LOG_FD ; then
> >> >> >> >> +  libc_cv_gnu_retain=yes
> >> >> >> >> +fi
> >> >> >> >> +rm -f conftest*])
> >> >> >> >> +if test $libc_cv_gnu_retain = yes; then
> >> >> >> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
> >> >> >> >> +fi
> >> >> >> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
> >> >> >> >> +
> >> >> >> >>   # Check if gcc warns about alias for function with incompatible types.
> >> >> >> >>   AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
> >> >> >> >>                libc_cv_gcc_incompatible_alias, [dnl
> >> >> >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
> >> >> >> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
> >> >> >> >>   AC_SUBST(libc_cv_z_execstack)
> >> >> >> >>
> >> >> >> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> >> >> >> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> >> >> >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
> >> >> >> >> +
> >> >> >> >>   LIBC_LINKER_FEATURE([--no-dynamic-linker],
> >> >> >> >>                     [-Wl,--no-dynamic-linker],
> >> >> >> >>                     [libc_cv_no_dynamic_linker=yes],
> >> >> >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
> >> >> >> >> index 546fc26a7b..127ea656c2 100644
> >> >> >> >> --- a/include/libc-symbols.h
> >> >> >> >> +++ b/include/libc-symbols.h
> >> >> >> >> @@ -352,6 +352,12 @@ for linking")
> >> >> >> >>
> >> >> >> >>   */
> >> >> >> >>
> >> >> >> >> +#ifdef HAVE_GNU_RETAIN
> >> >> >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
> >> >> >> >> +#else
> >> >> >> >> +# define attribute_used_retain __attribute__ ((__used__))
> >> >> >> >> +#endif
> >> >> >> >> +
> >> >> >> >>   /* Symbol set support macros.  */
> >> >> >> >>
> >> >> >> >>   /* Make SYMBOL, which is in the text segment, an element of SET.  */
> >> >> >> >> @@ -367,12 +373,12 @@ for linking")
> >> >> >> >>   /* When building a shared library, make the set section writable,
> >> >> >> >>      because it will need to be relocated at run time anyway.  */
> >> >> >> >>   # define _elf_set_element(set, symbol) \
> >> >> >> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> >> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >> >> >>   #else
> >> >> >> >>   # define _elf_set_element(set, symbol) \
> >> >> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> >> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> >> >> >> >>   #endif
> >> >> >> >>
> >> >> >> >>   /* Define SET as a symbol set.  This may be required (it is in a.out) to
> >> >> >> >> diff --git a/libio/Makefile b/libio/Makefile
> >> >> >> >> index 12ce41038f..ad0d53bb49 100644
> >> >> >> >> --- a/libio/Makefile
> >> >> >> >> +++ b/libio/Makefile
> >> >> >> >> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
> >> >> >> >>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
> >> >> >> >>                  $(objpfx)tst-bz24228-mem.out
> >> >> >> >>   endif
> >> >> >> >> +
> >> >> >> >> +tests += tst-cleanup-default tst-cleanup-default-static
> >> >> >> >> +tests-static += tst-cleanup-default-static
> >> >> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
> >> >> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> >> >> >> >> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
> >> >> >> >> +
> >> >> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> >> >> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
> >> >> >> >> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
> >> >> >> >> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
> >> >> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> >> >> >> >> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
> >> >> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
> >> >> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
> >> >> >> >> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
> >> >> >> >> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
> >> >> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
> >> >> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
> >> >> >> >> +endif
> >> >> >> >>   endif
> >> >> >> >>
> >> >> >> >>   include ../Rules
> >> >> >> >> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >> >> >> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >> >> >> >>   endif
> >> >> >> >>
> >> >> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> >> >> >> >> +       cmp $^ > $@; \
> >> >> >> >> +       $(evaluate-test)
> >> >> >> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
> >> >> >> >> +       $(compile.c) -o $@
> >> >> >> >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
> >> >> >> >> +       cmp $^ > $@; \
> >> >> >> >> +       $(evaluate-test)
> >> >> >> >> +$(objpfx)tst-cleanup-default-static.o: tst-cleanup.c
> >> >> >> >> +       $(compile.c) -o $@
> >> >> >> >> +
> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> >> >> >> >> +       cmp $^ > $@; \
> >> >> >> >> +       $(evaluate-test)
> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> >> >> >> >> +       $(compile.c) -o $@
> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
> >> >> >> >> +       cmp $^ > $@; \
> >> >> >> >> +       $(evaluate-test)
> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c
> >> >> >> >> +       $(compile.c) -o $@
> >> >> >> >
> >> >> >> >Please add a separate .c file for each test to get the correct dependency.
> >> >> >>
> >> >> >> Changed this block to:
> >> >> >>
> >> >> >> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >> >> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >> >> >>   endif
> >> >> >>
> >> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> >> >> >> +       cmp $^ > $@; \
> >> >> >> +       $(evaluate-test)
> >> >> >> +$(objpfx)tst-cleanup-default.c: tst-cleanup.c
> >> >> >> +       cp $< $@
> >> >> >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
> >> >> >> +       cmp $^ > $@; \
> >> >> >> +       $(evaluate-test)
> >> >> >> +$(objpfx)tst-cleanup-default-static.c: tst-cleanup.c
> >> >> >> +       cp $< $@
> >> >> >> +
> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> >> >> >> +       cmp $^ > $@; \
> >> >> >> +       $(evaluate-test)
> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> >> >> >> +       $(compile.c) -o $@
> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
> >> >> >> +       cmp $^ > $@; \
> >> >> >> +       $(evaluate-test)
> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static.c: tst-cleanup.c
> >> >> >> +       cp $< $@
> >> >> >> +
> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
> >> >> >> +       cmp $^ > $@; \
> >> >> >> +       $(evaluate-test)
> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc.c: tst-cleanup.c
> >> >> >> +       cp $< $@
> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc-static.out
> >> >> >> +       cmp $^ > $@; \
> >> >> >> +       $(evaluate-test)
> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-static.c: tst-cleanup.c
> >> >> >> +       cp $< $@
> >> >> >> +
> >> >> >>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
> >> >> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
> >> >> >>         $(common-objpfx)libio/; \
> >> >> >>
> >> >> >
> >> >> >"make clean" doesn't remove the generated files. The standard way in glibc
> >> >> >is to add a *-static.c source.
> >> >>
> >> >> I'll use .INTERMEDIATE and $(eval $(call ..))
> >> >>
> >> >> diff --git a/libio/Makefile b/libio/Makefile
> >> >> index 12ce41038f..a9b44f04df 100644
> >> >> --- a/libio/Makefile
> >> >> +++ b/libio/Makefile
> >> >> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
> >> >>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
> >> >>                  $(objpfx)tst-bz24228-mem.out
> >> >>   endif
> >> >> +
> >> >> +tests += tst-cleanup-default tst-cleanup-default-static
> >> >> +tests-static += tst-cleanup-default-static
> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> >> >> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
> >> >> +
> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
> >> >> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
> >> >> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> >> >> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
> >> >> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
> >> >> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
> >> >> +endif
> >> >>   endif
> >> >>
> >> >>   include ../Rules
> >> >> @@ -224,6 +244,17 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> >> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
> >> >>   endif
> >> >>
> >> >> +define gen-tst-cleanup
> >> >> +$(objpfx)tst-cleanup-$1-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-$1.out
> >> >> +       cmp $$^ > $$@; $$(evaluate-test)
> >> >> +$(objpfx)tst-cleanup-$1.c: tst-cleanup.c
> >> >> +       cp $$< $$@
> >> >> +.INTERMEDIATE: $(objpfx)tst-cleanup-$1.c
> >> >> +endef
> >> >> +
> >> >> +$(foreach t, default default-static start-stop-gc start-stop-gc-static nostart-stop-gc nostart-stop-gc-static, \
> >> >> +  $(eval $(call gen-tst-cleanup,$(t))))
> >> >> +
> >> >>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
> >> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
> >> >>         $(common-objpfx)libio/; \
> >> >
> >> >There are 2 issues with static tests:
> >> >
> >> >1. A separate static source is needed.
> >>
> >> .INTERMEDIATE perfectly solves the lingering copied source issue.
> >> I don't see lingering libio/tst-cleanup-*.c
> >
> >I was referring to
> >
> >elf/tst-array1-static.c
> >elf/tst-array5-static.c
> >elf/tst-dl-iter-static.c
> >elf/tst-dst-static.c
> >elf/tst-leaks1-static.c
> >elf/tst-libc_dlvsym-static.c
> >elf/tst-linkall-static.c
> >elf/tst-ptrguard1-static.c
> >elf/tst-single_threaded-pthread-static.c
> >elf/tst-single_threaded-static.c
> >elf/tst-stackguard1-static.c
> >elf/tst-tls1-static.c
> >elf/tst-tls2-static.c
> >elf/tst-tls9-static.c
> >elf/tst-tlsalign-extern-static.c
> >elf/tst-tlsalign-static.c
> >gmon/tst-gmon-static.c
> >gmon/tst-profile-static.c
> >localedata/bug-setlocale1-static.c
> >localedata/tst-langinfo-newlocale-static.c
> >localedata/tst-langinfo-setlocale-static.c
> >localedata/tst-langinfo-static.c
> >malloc/tst-malloc-usable-static.c
> >math/test-fpucw-ieee-static.c
> >math/test-fpucw-static.c
> >math/test-signgam-uchar-init-static.c
> >math/test-signgam-uchar-static.c
> >math/test-signgam-uint-init-static.c
> >math/test-signgam-uint-static.c
> >math/test-signgam-ullong-init-static.c
> >math/test-signgam-ullong-static.c
> >nptl/tst-mutex8-static.c
> >nptl/tst-mutexpi8-static.c
> >nptl/tst-sem11-static.c
> >nptl/tst-sem12-static.c
> >nptl/tst-setuid1-static.c
> >nptl/tst-stackguard1-static.c
> >nss/tst-nss-static.c
> >posix/tst-exec-static.c
> >posix/tst-spawn-static.c
> >setjmp/tst-setjmp-static.c
> >
> >> >2. We need to add the static test to both tests and tests-static.
> >>
> >> tests-static suffices. I have checked some tests-static usage in other
> >> directories.
> >
> >There are
> >
> >tests           := tst-setjmp jmpbug bug269-setjmp tst-setjmp-fp \
> >                   tst-sigsetjmp tst-setjmp-static
> >tests-static    := tst-setjmp-static
> >
> >They should be replaced by something like
> >
> >tests           := tst-setjmp jmpbug bug269-setjmp tst-setjmp-fp \
> >                   tst-sigsetjmp
> >tests-static-add := tst-setjmp-static
>
> Re-checking, the tst-cleanup* targets are in tests-special so `make tests` will build them.
> If a tests-static target is not in tests-internal/tests-special, looks like it needs to be in tests.
>
> As is, I think my usage is correct.
>

The current glibc convention is to use

[hjl@gnu-cfl-2 x86-glibc]$ cat elf/tst-tls9-static.c
#include "tst-tls9.c"
[hjl@gnu-cfl-2 x86-glibc]$

to test both dynamic and static libc.  If we want to use a single
source, we should create
a framework to cover all such tests.
  

On 2021-04-05, H.J. Lu wrote:
>On Mon, Apr 5, 2021 at 2:03 PM Fangrui Song <maskray@google.com> wrote:
>>
>> On 2021-04-05, H.J. Lu wrote:
>> >On Mon, Apr 5, 2021 at 11:17 AM Fangrui Song <maskray@google.com> wrote:
>> >>
>> >> On 2021-04-04, H.J. Lu wrote:
>> >> >On Sat, Apr 3, 2021 at 2:57 PM Fangrui Song <maskray@google.com> wrote:
>> >> >>
>> >> >> On 2021-04-03, H.J. Lu wrote:
>> >> >> >On Sat, Apr 3, 2021 at 11:02 AM Fangrui Song <maskray@google.com> wrote:
>> >> >> >>
>> >> >> >>
>> >> >> >> On 2021-04-02, H.J. Lu wrote:
>> >> >> >> >On Thu, Apr 1, 2021 at 8:23 PM Fangrui Song <maskray@google.com> wrote:
>> >> >> >> >>
>> >> >> >> >> On 2021-04-01, H.J. Lu wrote:
>> >> >> >> >> >On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song <maskray@google.com> wrote:
>> >> >> >> >> >>
>> >> >> >> >> >> So that text_set_element/data_set_element/bss_set_element defined
>> >> >> >> >> >> variables will be retained by the linker.
>> >> >> >> >> >>
>> >> >> >> >> >> Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
>> >> >> >> >> >> will not be optimized out; 'retain' prevents section garbage collection
>> >> >> >> >> >> if the linker support SHF_GNU_RETAIN.
>> >> >> >> >> >>
>> >> >> >> >> >> GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
>> >> >> >> >> >> identifier name sections to be GCed even if there are live
>> >> >> >> >> >> __start_/__stop_ references.
>> >> >> >> >> >>
>> >> >> >> >> >> Without the change, there are some static linking problems, e.g.
>> >> >> >> >> >> _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
>> >> >> >> >> >> stdout is not flushed on exit.
>> >> >> >> >> >>
>> >> >> >> >> >> Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
>> >> >> >> >> >> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
>> >> >> >> >> >> ---
>> >> >> >> >> >> Changes in v1 -> v2:
>> >> >> >> >> >> * Define attribute_used_retain_section
>> >> >> >> >> >> Changes in v2 -> v3:
>> >> >> >> >> >> * Use attribute_used_retain instead attribute_used_retain_section
>> >> >> >> >> >> Changes in v3 -> v4:
>> >> >> >> >> >> * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
>> >> >> >> >> >> Changes in v4 -> v5:
>> >> >> >> >> >> * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
>> >> >> >> >> >> * Rename *gcc_retain* to *gnu_retain*
>> >> >> >> >> >> ---
>> >> >> >> >> >>  config.h.in            |  3 +++
>> >> >> >> >> >>  configure              | 59 ++++++++++++++++++++++++++++++++++++++++++
>> >> >> >> >> >>  configure.ac           | 21 +++++++++++++++
>> >> >> >> >> >>  include/libc-symbols.h | 14 +++++++---
>> >> >> >> >> >>  libio/Makefile         | 32 +++++++++++++++++++++++
>> >> >> >> >> >>  libio/tst-cleanup.c    | 33 +++++++++++++++++++++++
>> >> >> >> >> >>  libio/tst-cleanup.exp  |  1 +
>> >> >> >> >> >>  7 files changed, 159 insertions(+), 4 deletions(-)
>> >> >> >> >> >>  create mode 100644 libio/tst-cleanup.c
>> >> >> >> >> >>  create mode 100644 libio/tst-cleanup.exp
>> >> >> >> >> >>
>> >> >> >> >> >> diff --git a/config.h.in b/config.h.in
>> >> >> >> >> >> index ca1547ae67..96a08c7757 100644
>> >> >> >> >> >> --- a/config.h.in
>> >> >> >> >> >> +++ b/config.h.in
>> >> >> >> >> >> @@ -187,6 +187,9 @@
>> >> >> >> >> >>  /* Define if gcc supports attribute ifunc.  */
>> >> >> >> >> >>  #undef HAVE_GCC_IFUNC
>> >> >> >> >> >>
>> >> >> >> >> >> +/* Define if CC supports attribute retain.  */
>> >> >> >> >> >> +#undef HAVE_GNU_RETAIN
>> >> >> >> >> >> +
>> >> >> >> >> >>  /* Define if the linker defines __ehdr_start.  */
>> >> >> >> >> >>  #undef HAVE_EHDR_START
>> >> >> >> >> >>
>> >> >> >> >> >> diff --git a/configure b/configure
>> >> >> >> >> >> index fcf43bf7de..e64b7f8efe 100755
>> >> >> >> >> >> --- a/configure
>> >> >> >> >> >> +++ b/configure
>> >> >> >> >> >> @@ -4105,6 +4105,31 @@ fi
>> >> >> >> >> >>  $as_echo "$libc_cv_textrel_ifunc" >&6; }
>> >> >> >> >> >>
>> >> >> >> >> >>
>> >> >> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
>> >> >> >> >> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
>> >> >> >> >> >> +if ${libc_cv_gnu_retain+:} false; then :
>> >> >> >> >> >> +  $as_echo_n "(cached) " >&6
>> >> >> >> >> >> +else
>> >> >> >> >> >> +  cat > conftest.c <<EOF
>> >> >> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> >> >> >> >> +EOF
>> >> >> >> >> >> +libc_cv_gnu_retain=no
>> >> >> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
>> >> >> >> >> >> +   2>&5 ; then
>> >> >> >> >> >> +  libc_cv_gnu_retain=yes
>> >> >> >> >> >> +fi
>> >> >> >> >> >> +rm -f conftest*
>> >> >> >> >> >> +fi
>> >> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
>> >> >> >> >> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
>> >> >> >> >> >> +if test $libc_cv_gnu_retain = yes; then
>> >> >> >> >> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
>> >> >> >> >> >> +
>> >> >> >> >> >> +fi
>> >> >> >> >> >> +config_vars="$config_vars
>> >> >> >> >> >> +have-gnu-retain = $libc_cv_gnu_retain"
>> >> >> >> >> >> +
>> >> >> >> >> >>  # Check if gcc warns about alias for function with incompatible types.
>> >> >> >> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
>> >> >> >> >> >>  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
>> >> >> >> >> >> @@ -5871,6 +5896,40 @@ fi
>> >> >> >> >> >>  $as_echo "$libc_linker_feature" >&6; }
>> >> >> >> >> >>
>> >> >> >> >> >>
>> >> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
>> >> >> >> >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
>> >> >> >> >> >> +libc_linker_feature=no
>> >> >> >> >> >> +if test x"$gnu_ld" = x"yes"; then
>> >> >> >> >> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
>> >> >> >> >> >> +  if test -n "$libc_linker_check"; then
>> >> >> >> >> >> +    cat > conftest.c <<EOF
>> >> >> >> >> >> +int _start (void) { return 42; }
>> >> >> >> >> >> +EOF
>> >> >> >> >> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
>> >> >> >> >> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
>> >> >> >> >> >> +                               -fPIC -shared -o conftest.so conftest.c
>> >> >> >> >> >> +                               1>&5'
>> >> >> >> >> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
>> >> >> >> >> >> +  (eval $ac_try) 2>&5
>> >> >> >> >> >> +  ac_status=$?
>> >> >> >> >> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
>> >> >> >> >> >> +  test $ac_status = 0; }; }
>> >> >> >> >> >> +    then
>> >> >> >> >> >> +      libc_linker_feature=yes
>> >> >> >> >> >> +    fi
>> >> >> >> >> >> +    rm -f conftest*
>> >> >> >> >> >> +  fi
>> >> >> >> >> >> +fi
>> >> >> >> >> >> +if test $libc_linker_feature = yes; then
>> >> >> >> >> >> +  libc_cv_z_start_stop_gc=yes
>> >> >> >> >> >> +else
>> >> >> >> >> >> +  libc_cv_z_start_stop_gc=no
>> >> >> >> >> >> +fi
>> >> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
>> >> >> >> >> >> +$as_echo "$libc_linker_feature" >&6; }
>> >> >> >> >> >> +config_vars="$config_vars
>> >> >> >> >> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
>> >> >> >> >> >> +
>> >> >> >> >> >>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>> >> >> >> >> >>  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>> >> >> >> >> >>  libc_linker_feature=no
>> >> >> >> >> >> diff --git a/configure.ac b/configure.ac
>> >> >> >> >> >> index fce967f2c2..cc47e56e82 100644
>> >> >> >> >> >> --- a/configure.ac
>> >> >> >> >> >> +++ b/configure.ac
>> >> >> >> >> >> @@ -707,6 +707,23 @@ fi
>> >> >> >> >> >>  rm -f conftest*])
>> >> >> >> >> >>  AC_SUBST(libc_cv_textrel_ifunc)
>> >> >> >> >> >>
>> >> >> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> >> >> >> >> +AC_CACHE_CHECK([for GNU attribute retain support],
>> >> >> >> >> >> +              libc_cv_gnu_retain, [dnl
>> >> >> >> >> >> +cat > conftest.c <<EOF
>> >> >> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> >> >> >> >> +EOF
>> >> >> >> >> >> +libc_cv_gnu_retain=no
>> >> >> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
>> >> >> >> >> >> +   2>&AS_MESSAGE_LOG_FD ; then
>> >> >> >> >> >> +  libc_cv_gnu_retain=yes
>> >> >> >> >> >> +fi
>> >> >> >> >> >> +rm -f conftest*])
>> >> >> >> >> >> +if test $libc_cv_gnu_retain = yes; then
>> >> >> >> >> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
>> >> >> >> >> >> +fi
>> >> >> >> >> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
>> >> >> >> >> >> +
>> >> >> >> >> >>  # Check if gcc warns about alias for function with incompatible types.
>> >> >> >> >> >>  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>> >> >> >> >> >>                libc_cv_gcc_incompatible_alias, [dnl
>> >> >> >> >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>> >> >> >> >> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>> >> >> >> >> >>  AC_SUBST(libc_cv_z_execstack)
>> >> >> >> >> >>
>> >> >> >> >> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
>> >> >> >> >> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
>> >> >> >> >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
>> >> >> >> >> >> +
>> >> >> >> >> >>  LIBC_LINKER_FEATURE([--no-dynamic-linker],
>> >> >> >> >> >>                     [-Wl,--no-dynamic-linker],
>> >> >> >> >> >>                     [libc_cv_no_dynamic_linker=yes],
>> >> >> >> >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
>> >> >> >> >> >> index 546fc26a7b..127ea656c2 100644
>> >> >> >> >> >> --- a/include/libc-symbols.h
>> >> >> >> >> >> +++ b/include/libc-symbols.h
>> >> >> >> >> >> @@ -352,6 +352,12 @@ for linking")
>> >> >> >> >> >>
>> >> >> >> >> >>  */
>> >> >> >> >> >>
>> >> >> >> >> >> +#ifdef HAVE_GNU_RETAIN
>> >> >> >> >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
>> >> >> >> >> >> +#else
>> >> >> >> >> >> +# define attribute_used_retain __attribute__ ((__used__))
>> >> >> >> >> >> +#endif
>> >> >> >> >> >> +
>> >> >> >> >> >>  /* Symbol set support macros.  */
>> >> >> >> >> >>
>> >> >> >> >> >>  /* Make SYMBOL, which is in the text segment, an element of SET.  */
>> >> >> >> >> >> @@ -367,12 +373,12 @@ for linking")
>> >> >> >> >> >>  /* When building a shared library, make the set section writable,
>> >> >> >> >> >>     because it will need to be relocated at run time anyway.  */
>> >> >> >> >> >>  # define _elf_set_element(set, symbol) \
>> >> >> >> >> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
>> >> >> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> >> >> >> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
>> >> >> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >> >> >> >> >>  #else
>> >> >> >> >> >>  # define _elf_set_element(set, symbol) \
>> >> >> >> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> >> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> >> >> >> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> >> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >> >> >> >> >>  #endif
>> >> >> >> >> >>
>> >> >> >> >> >>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
>> >> >> >> >> >> diff --git a/libio/Makefile b/libio/Makefile
>> >> >> >> >> >> index 12ce41038f..c9c232ebc2 100644
>> >> >> >> >> >> --- a/libio/Makefile
>> >> >> >> >> >> +++ b/libio/Makefile
>> >> >> >> >> >> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared))
>> >> >> >> >> >>  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>> >> >> >> >> >>                  $(objpfx)tst-bz24228-mem.out
>> >> >> >> >> >>  endif
>> >> >> >> >> >> +
>> >> >> >> >> >> +tests += tst-cleanup-default
>> >> >> >> >> >> +tests-static += tst-cleanup-default
>> >> >> >> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out
>> >> >> >> >> >
>> >> >> >> >> >Please make 2 tests,  tst-cleanup-default and tst-cleanup-default-static.
>> >> >> >> >>
>> >> >> >> >> Added.
>> >> >> >> >>
>> >> >> >> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> >> >> >> >> >> +
>> >> >> >> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> >> >> >> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
>> >> >> >> >> >> +tests-static += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
>> >> >> >> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> >> >> >> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
>> >> >> >> >> >
>> >> >> >> >> >Same here.
>> >> >> >> >>
>> >> >> >> >> Added.
>> >> >> >> >>
>> >> >> >> >> >> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
>> >> >> >> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc
>> >> >> >> >> >> +endif
>> >> >> >> >> >>  endif
>> >> >> >> >> >>
>> >> >> >> >> >>  include ../Rules
>> >> >> >> >> >> @@ -224,6 +238,24 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>> >> >> >> >> >>  $(objpfx)tst-wfile-sync.out: $(gen-locales)
>> >> >> >> >> >>  endif
>> >> >> >> >> >>
>> >> >> >> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> >> >> >> >> >> +       cmp $^ > $@; \
>> >> >> >> >> >> +       $(evaluate-test)
>> >> >> >> >> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
>> >> >> >> >> >> +       $(compile.c) -o $@
>> >> >> >> >> >> +
>> >> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> >> >> >> >> >> +       cmp $^ > $@; \
>> >> >> >> >> >> +       $(evaluate-test)
>> >> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> >> >> >> >> >> +       $(compile.c) -o $@
>> >> >> >> >> >> +
>> >> >> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
>> >> >> >> >> >> +       cmp $^ > $@; \
>> >> >> >> >> >> +       $(evaluate-test)
>> >> >> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
>> >> >> >> >> >> +       $(compile.c) -o $@
>> >> >> >> >> >>
>> >> >> >> >> >>  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>> >> >> >> >> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>> >> >> >> >> >>         $(common-objpfx)libio/; \
>> >> >> >> >> >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
>> >> >> >> >> >> new file mode 100644
>> >> >> >> >> >> index 0000000000..7f0a34a91e
>> >> >> >> >> >> --- /dev/null
>> >> >> >> >> >> +++ b/libio/tst-cleanup.c
>> >> >> >> >> >> @@ -0,0 +1,33 @@
>> >> >> >> >> >
>> >> >> >> >> >Please add a comment saying that test --gc-sections.
>> >> >> >> >>
>> >> >> >> >> OK, added.
>> >> >> >> >>
>> >> >> >> >> >> +/* Copyright (C) 2021 Free Software Foundation, Inc.
>> >> >> >> >> >> +   This file is part of the GNU C Library.
>> >> >> >> >> >> +
>> >> >> >> >> >> +   The GNU C Library is free software; you can redistribute it and/or
>> >> >> >> >> >> +   modify it under the terms of the GNU Lesser General Public
>> >> >> >> >> >> +   License as published by the Free Software Foundation; either
>> >> >> >> >> >> +   version 2.1 of the License, or (at your option) any later version.
>> >> >> >> >> >> +
>> >> >> >> >> >> +   The GNU C Library is distributed in the hope that it will be useful,
>> >> >> >> >> >> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>> >> >> >> >> >> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> >> >> >> >> >> +   Lesser General Public License for more details.
>> >> >> >> >> >> +
>> >> >> >> >> >> +   You should have received a copy of the GNU Lesser General Public
>> >> >> >> >> >> +   License along with the GNU C Library; if not, see
>> >> >> >> >> >> +   <https://www.gnu.org/licenses/>.  */
>> >> >> >> >> >> +
>> >> >> >> >> >> +/* Test that stdout is flushed after atexit callbacks were run.  */
>> >> >> >> >> >> +
>> >> >> >> >> >> +#include <stdio.h>
>> >> >> >> >> >> +#include <stdlib.h>
>> >> >> >> >> >> +
>> >> >> >> >> >> +void
>> >> >> >> >> >> +hook (void)
>> >> >> >> >> >> +{
>> >> >> >> >> >> +  puts ("hello");
>> >> >> >> >> >> +}
>> >> >> >> >> >> +
>> >> >> >> >> >> +int
>> >> >> >> >> >> +main (void)
>> >> >> >> >> >> +{
>> >> >> >> >> >> +  atexit (hook);
>> >> >> >> >> >> +}
>> >> >> >> >> >> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
>> >> >> >> >> >> new file mode 100644
>> >> >> >> >> >> index 0000000000..ce01362503
>> >> >> >> >> >> --- /dev/null
>> >> >> >> >> >> +++ b/libio/tst-cleanup.exp
>> >> >> >> >> >> @@ -0,0 +1 @@
>> >> >> >> >> >> +hello
>> >> >> >> >> >> --
>> >> >> >> >> >> 2.31.0.291.g576ba9dcdaf-goog
>> >> >> >> >> >>
>> >> >> >> >> >
>> >> >> >> >>
>> >> >> >> >> diff --git a/config.h.in b/config.h.in
>> >> >> >> >> index ca1547ae67..96a08c7757 100644
>> >> >> >> >> --- a/config.h.in
>> >> >> >> >> +++ b/config.h.in
>> >> >> >> >> @@ -187,6 +187,9 @@
>> >> >> >> >>   /* Define if gcc supports attribute ifunc.  */
>> >> >> >> >>   #undef HAVE_GCC_IFUNC
>> >> >> >> >>
>> >> >> >> >> +/* Define if CC supports attribute retain.  */
>> >> >> >> >> +#undef HAVE_GNU_RETAIN
>> >> >> >> >> +
>> >> >> >> >>   /* Define if the linker defines __ehdr_start.  */
>> >> >> >> >>   #undef HAVE_EHDR_START
>> >> >> >> >>
>> >> >> >> >> diff --git a/configure b/configure
>> >> >> >> >> index fcf43bf7de..e64b7f8efe 100755
>> >> >> >> >> --- a/configure
>> >> >> >> >> +++ b/configure
>> >> >> >> >> @@ -4105,6 +4105,31 @@ fi
>> >> >> >> >>   $as_echo "$libc_cv_textrel_ifunc" >&6; }
>> >> >> >> >>
>> >> >> >> >>
>> >> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
>> >> >> >> >> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
>> >> >> >> >> +if ${libc_cv_gnu_retain+:} false; then :
>> >> >> >> >> +  $as_echo_n "(cached) " >&6
>> >> >> >> >> +else
>> >> >> >> >> +  cat > conftest.c <<EOF
>> >> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> >> >> >> +EOF
>> >> >> >> >> +libc_cv_gnu_retain=no
>> >> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
>> >> >> >> >> +   2>&5 ; then
>> >> >> >> >> +  libc_cv_gnu_retain=yes
>> >> >> >> >> +fi
>> >> >> >> >> +rm -f conftest*
>> >> >> >> >> +fi
>> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
>> >> >> >> >> +$as_echo "$libc_cv_gnu_retain" >&6; }
>> >> >> >> >> +if test $libc_cv_gnu_retain = yes; then
>> >> >> >> >> +  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
>> >> >> >> >> +
>> >> >> >> >> +fi
>> >> >> >> >> +config_vars="$config_vars
>> >> >> >> >> +have-gnu-retain = $libc_cv_gnu_retain"
>> >> >> >> >> +
>> >> >> >> >>   # Check if gcc warns about alias for function with incompatible types.
>> >> >> >> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
>> >> >> >> >>   $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
>> >> >> >> >> @@ -5871,6 +5896,40 @@ fi
>> >> >> >> >>   $as_echo "$libc_linker_feature" >&6; }
>> >> >> >> >>
>> >> >> >> >>
>> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
>> >> >> >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
>> >> >> >> >> +libc_linker_feature=no
>> >> >> >> >> +if test x"$gnu_ld" = x"yes"; then
>> >> >> >> >> +  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
>> >> >> >> >> +  if test -n "$libc_linker_check"; then
>> >> >> >> >> +    cat > conftest.c <<EOF
>> >> >> >> >> +int _start (void) { return 42; }
>> >> >> >> >> +EOF
>> >> >> >> >> +    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
>> >> >> >> >> +                               -Wl,-z,start-stop-gc -nostdlib -nostartfiles
>> >> >> >> >> +                               -fPIC -shared -o conftest.so conftest.c
>> >> >> >> >> +                               1>&5'
>> >> >> >> >> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
>> >> >> >> >> +  (eval $ac_try) 2>&5
>> >> >> >> >> +  ac_status=$?
>> >> >> >> >> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
>> >> >> >> >> +  test $ac_status = 0; }; }
>> >> >> >> >> +    then
>> >> >> >> >> +      libc_linker_feature=yes
>> >> >> >> >> +    fi
>> >> >> >> >> +    rm -f conftest*
>> >> >> >> >> +  fi
>> >> >> >> >> +fi
>> >> >> >> >> +if test $libc_linker_feature = yes; then
>> >> >> >> >> +  libc_cv_z_start_stop_gc=yes
>> >> >> >> >> +else
>> >> >> >> >> +  libc_cv_z_start_stop_gc=no
>> >> >> >> >> +fi
>> >> >> >> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
>> >> >> >> >> +$as_echo "$libc_linker_feature" >&6; }
>> >> >> >> >> +config_vars="$config_vars
>> >> >> >> >> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
>> >> >> >> >> +
>> >> >> >> >>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>> >> >> >> >>   $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>> >> >> >> >>   libc_linker_feature=no
>> >> >> >> >> diff --git a/configure.ac b/configure.ac
>> >> >> >> >> index fce967f2c2..cc47e56e82 100644
>> >> >> >> >> --- a/configure.ac
>> >> >> >> >> +++ b/configure.ac
>> >> >> >> >> @@ -707,6 +707,23 @@ fi
>> >> >> >> >>   rm -f conftest*])
>> >> >> >> >>   AC_SUBST(libc_cv_textrel_ifunc)
>> >> >> >> >>
>> >> >> >> >> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
>> >> >> >> >> +AC_CACHE_CHECK([for GNU attribute retain support],
>> >> >> >> >> +              libc_cv_gnu_retain, [dnl
>> >> >> >> >> +cat > conftest.c <<EOF
>> >> >> >> >> +static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
>> >> >> >> >> +EOF
>> >> >> >> >> +libc_cv_gnu_retain=no
>> >> >> >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
>> >> >> >> >> +   2>&AS_MESSAGE_LOG_FD ; then
>> >> >> >> >> +  libc_cv_gnu_retain=yes
>> >> >> >> >> +fi
>> >> >> >> >> +rm -f conftest*])
>> >> >> >> >> +if test $libc_cv_gnu_retain = yes; then
>> >> >> >> >> +  AC_DEFINE(HAVE_GNU_RETAIN)
>> >> >> >> >> +fi
>> >> >> >> >> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
>> >> >> >> >> +
>> >> >> >> >>   # Check if gcc warns about alias for function with incompatible types.
>> >> >> >> >>   AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>> >> >> >> >>                libc_cv_gcc_incompatible_alias, [dnl
>> >> >> >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>> >> >> >> >>                     [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>> >> >> >> >>   AC_SUBST(libc_cv_z_execstack)
>> >> >> >> >>
>> >> >> >> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
>> >> >> >> >> +                   [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
>> >> >> >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
>> >> >> >> >> +
>> >> >> >> >>   LIBC_LINKER_FEATURE([--no-dynamic-linker],
>> >> >> >> >>                     [-Wl,--no-dynamic-linker],
>> >> >> >> >>                     [libc_cv_no_dynamic_linker=yes],
>> >> >> >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
>> >> >> >> >> index 546fc26a7b..127ea656c2 100644
>> >> >> >> >> --- a/include/libc-symbols.h
>> >> >> >> >> +++ b/include/libc-symbols.h
>> >> >> >> >> @@ -352,6 +352,12 @@ for linking")
>> >> >> >> >>
>> >> >> >> >>   */
>> >> >> >> >>
>> >> >> >> >> +#ifdef HAVE_GNU_RETAIN
>> >> >> >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
>> >> >> >> >> +#else
>> >> >> >> >> +# define attribute_used_retain __attribute__ ((__used__))
>> >> >> >> >> +#endif
>> >> >> >> >> +
>> >> >> >> >>   /* Symbol set support macros.  */
>> >> >> >> >>
>> >> >> >> >>   /* Make SYMBOL, which is in the text segment, an element of SET.  */
>> >> >> >> >> @@ -367,12 +373,12 @@ for linking")
>> >> >> >> >>   /* When building a shared library, make the set section writable,
>> >> >> >> >>      because it will need to be relocated at run time anyway.  */
>> >> >> >> >>   # define _elf_set_element(set, symbol) \
>> >> >> >> >> -  static const void *__elf_set_##set##_element_##symbol##__ \
>> >> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> >> >> >> +    static const void *__elf_set_##set##_element_##symbol##__ \
>> >> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >> >> >> >>   #else
>> >> >> >> >>   # define _elf_set_element(set, symbol) \
>> >> >> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> >> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> >> >> >> +    static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> >> >> >> +      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
>> >> >> >> >>   #endif
>> >> >> >> >>
>> >> >> >> >>   /* Define SET as a symbol set.  This may be required (it is in a.out) to
>> >> >> >> >> diff --git a/libio/Makefile b/libio/Makefile
>> >> >> >> >> index 12ce41038f..ad0d53bb49 100644
>> >> >> >> >> --- a/libio/Makefile
>> >> >> >> >> +++ b/libio/Makefile
>> >> >> >> >> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
>> >> >> >> >>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>> >> >> >> >>                  $(objpfx)tst-bz24228-mem.out
>> >> >> >> >>   endif
>> >> >> >> >> +
>> >> >> >> >> +tests += tst-cleanup-default tst-cleanup-default-static
>> >> >> >> >> +tests-static += tst-cleanup-default-static
>> >> >> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
>> >> >> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> >> >> >> >> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
>> >> >> >> >> +
>> >> >> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> >> >> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
>> >> >> >> >> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
>> >> >> >> >> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
>> >> >> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> >> >> >> >> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
>> >> >> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
>> >> >> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
>> >> >> >> >> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
>> >> >> >> >> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
>> >> >> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
>> >> >> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
>> >> >> >> >> +endif
>> >> >> >> >>   endif
>> >> >> >> >>
>> >> >> >> >>   include ../Rules
>> >> >> >> >> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>> >> >> >> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>> >> >> >> >>   endif
>> >> >> >> >>
>> >> >> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> >> >> >> >> +       cmp $^ > $@; \
>> >> >> >> >> +       $(evaluate-test)
>> >> >> >> >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
>> >> >> >> >> +       $(compile.c) -o $@
>> >> >> >> >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
>> >> >> >> >> +       cmp $^ > $@; \
>> >> >> >> >> +       $(evaluate-test)
>> >> >> >> >> +$(objpfx)tst-cleanup-default-static.o: tst-cleanup.c
>> >> >> >> >> +       $(compile.c) -o $@
>> >> >> >> >> +
>> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> >> >> >> >> +       cmp $^ > $@; \
>> >> >> >> >> +       $(evaluate-test)
>> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> >> >> >> >> +       $(compile.c) -o $@
>> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
>> >> >> >> >> +       cmp $^ > $@; \
>> >> >> >> >> +       $(evaluate-test)
>> >> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c
>> >> >> >> >> +       $(compile.c) -o $@
>> >> >> >> >
>> >> >> >> >Please add a separate .c file for each test to get the correct dependency.
>> >> >> >>
>> >> >> >> Changed this block to:
>> >> >> >>
>> >> >> >> @@ -224,6 +244,39 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>> >> >> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>> >> >> >>   endif
>> >> >> >>
>> >> >> >> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
>> >> >> >> +       cmp $^ > $@; \
>> >> >> >> +       $(evaluate-test)
>> >> >> >> +$(objpfx)tst-cleanup-default.c: tst-cleanup.c
>> >> >> >> +       cp $< $@
>> >> >> >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default-static.out
>> >> >> >> +       cmp $^ > $@; \
>> >> >> >> +       $(evaluate-test)
>> >> >> >> +$(objpfx)tst-cleanup-default-static.c: tst-cleanup.c
>> >> >> >> +       cp $< $@
>> >> >> >> +
>> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
>> >> >> >> +       cmp $^ > $@; \
>> >> >> >> +       $(evaluate-test)
>> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
>> >> >> >> +       $(compile.c) -o $@
>> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc-static.out
>> >> >> >> +       cmp $^ > $@; \
>> >> >> >> +       $(evaluate-test)
>> >> >> >> +$(objpfx)tst-cleanup-start-stop-gc-static.c: tst-cleanup.c
>> >> >> >> +       cp $< $@
>> >> >> >> +
>> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
>> >> >> >> +       cmp $^ > $@; \
>> >> >> >> +       $(evaluate-test)
>> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc.c: tst-cleanup.c
>> >> >> >> +       cp $< $@
>> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc-static.out
>> >> >> >> +       cmp $^ > $@; \
>> >> >> >> +       $(evaluate-test)
>> >> >> >> +$(objpfx)tst-cleanup-nostart-stop-gc-static.c: tst-cleanup.c
>> >> >> >> +       cp $< $@
>> >> >> >> +
>> >> >> >>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>> >> >> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>> >> >> >>         $(common-objpfx)libio/; \
>> >> >> >>
>> >> >> >
>> >> >> >"make clean" doesn't remove the generated files. The standard way in glibc
>> >> >> >is to add a *-static.c source.
>> >> >>
>> >> >> I'll use .INTERMEDIATE and $(eval $(call ..))
>> >> >>
>> >> >> diff --git a/libio/Makefile b/libio/Makefile
>> >> >> index 12ce41038f..a9b44f04df 100644
>> >> >> --- a/libio/Makefile
>> >> >> +++ b/libio/Makefile
>> >> >> @@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
>> >> >>   tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
>> >> >>                  $(objpfx)tst-bz24228-mem.out
>> >> >>   endif
>> >> >> +
>> >> >> +tests += tst-cleanup-default tst-cleanup-default-static
>> >> >> +tests-static += tst-cleanup-default-static
>> >> >> +tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
>> >> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> >> >> +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
>> >> >> +
>> >> >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>> >> >> +tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
>> >> >> +               tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
>> >> >> +tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
>> >> >> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
>> >> >> +               $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
>> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
>> >> >> +               $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
>> >> >> +LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
>> >> >> +LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
>> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
>> >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
>> >> >> +endif
>> >> >>   endif
>> >> >>
>> >> >>   include ../Rules
>> >> >> @@ -224,6 +244,17 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
>> >> >>   $(objpfx)tst-wfile-sync.out: $(gen-locales)
>> >> >>   endif
>> >> >>
>> >> >> +define gen-tst-cleanup
>> >> >> +$(objpfx)tst-cleanup-$1-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-$1.out
>> >> >> +       cmp $$^ > $$@; $$(evaluate-test)
>> >> >> +$(objpfx)tst-cleanup-$1.c: tst-cleanup.c
>> >> >> +       cp $$< $$@
>> >> >> +.INTERMEDIATE: $(objpfx)tst-cleanup-$1.c
>> >> >> +endef
>> >> >> +
>> >> >> +$(foreach t, default default-static start-stop-gc start-stop-gc-static nostart-stop-gc nostart-stop-gc-static, \
>> >> >> +  $(eval $(call gen-tst-cleanup,$(t))))
>> >> >> +
>> >> >>   $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
>> >> >>         $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'   \
>> >> >>         $(common-objpfx)libio/; \
>> >> >
>> >> >There are 2 issues with static tests:
>> >> >
>> >> >1. A separate static source is needed.
>> >>
>> >> .INTERMEDIATE perfectly solves the lingering copied source issue.
>> >> I don't see lingering libio/tst-cleanup-*.c
>> >
>> >I was referring to
>> >
>> >elf/tst-array1-static.c
>> >elf/tst-array5-static.c
>> >elf/tst-dl-iter-static.c
>> >elf/tst-dst-static.c
>> >elf/tst-leaks1-static.c
>> >elf/tst-libc_dlvsym-static.c
>> >elf/tst-linkall-static.c
>> >elf/tst-ptrguard1-static.c
>> >elf/tst-single_threaded-pthread-static.c
>> >elf/tst-single_threaded-static.c
>> >elf/tst-stackguard1-static.c
>> >elf/tst-tls1-static.c
>> >elf/tst-tls2-static.c
>> >elf/tst-tls9-static.c
>> >elf/tst-tlsalign-extern-static.c
>> >elf/tst-tlsalign-static.c
>> >gmon/tst-gmon-static.c
>> >gmon/tst-profile-static.c
>> >localedata/bug-setlocale1-static.c
>> >localedata/tst-langinfo-newlocale-static.c
>> >localedata/tst-langinfo-setlocale-static.c
>> >localedata/tst-langinfo-static.c
>> >malloc/tst-malloc-usable-static.c
>> >math/test-fpucw-ieee-static.c
>> >math/test-fpucw-static.c
>> >math/test-signgam-uchar-init-static.c
>> >math/test-signgam-uchar-static.c
>> >math/test-signgam-uint-init-static.c
>> >math/test-signgam-uint-static.c
>> >math/test-signgam-ullong-init-static.c
>> >math/test-signgam-ullong-static.c
>> >nptl/tst-mutex8-static.c
>> >nptl/tst-mutexpi8-static.c
>> >nptl/tst-sem11-static.c
>> >nptl/tst-sem12-static.c
>> >nptl/tst-setuid1-static.c
>> >nptl/tst-stackguard1-static.c
>> >nss/tst-nss-static.c
>> >posix/tst-exec-static.c
>> >posix/tst-spawn-static.c
>> >setjmp/tst-setjmp-static.c
>> >
>> >> >2. We need to add the static test to both tests and tests-static.
>> >>
>> >> tests-static suffices. I have checked some tests-static usage in other
>> >> directories.
>> >
>> >There are
>> >
>> >tests           := tst-setjmp jmpbug bug269-setjmp tst-setjmp-fp \
>> >                   tst-sigsetjmp tst-setjmp-static
>> >tests-static    := tst-setjmp-static
>> >
>> >They should be replaced by something like
>> >
>> >tests           := tst-setjmp jmpbug bug269-setjmp tst-setjmp-fp \
>> >                   tst-sigsetjmp
>> >tests-static-add := tst-setjmp-static
>>
>> Re-checking, the tst-cleanup* targets are in tests-special so `make tests` will build them.
>> If a tests-static target is not in tests-internal/tests-special, looks like it needs to be in tests.
>>
>> As is, I think my usage is correct.
>>
>
>The current glibc convention is to use
>
>[hjl@gnu-cfl-2 x86-glibc]$ cat elf/tst-tls9-static.c
>#include "tst-tls9.c"
>[hjl@gnu-cfl-2 x86-glibc]$
>
>to test both dynamic and static libc.  If we want to use a single
>source, we should create
>a framework to cover all such tests.

OK. Dropped cp $< $@ and .INTERMEDIATE


 From e937ae26a4a9a8ff6b1198f347f0b141a9285305 Mon Sep 17 00:00:00 2001
From: Fangrui Song <maskray@google.com>
Date: Tue, 6 Apr 2021 14:45:01 -0700
Subject: [PATCH] Set the retain attribute on _elf_set_element if CC supports
  [BZ #27492]
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

So that text_set_element/data_set_element/bss_set_element defined
variables will be retained by the linker.

Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
will not be optimized out; 'retain' prevents section garbage collection
if the linker support SHF_GNU_RETAIN.

GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
identifier name sections to be GCed even if there are live
__start_/__stop_ references.

Without the change, there are some static linking problems, e.g.
_IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
stdout is not flushed on exit.

Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
---
  config.h.in                                |  3 ++
  configure                                  | 59 ++++++++++++++++++++++
  configure.ac                               | 21 ++++++++
  include/libc-symbols.h                     | 14 +++--
  libio/Makefile                             | 28 ++++++++++
  libio/tst-cleanup-default-static.c         |  1 +
  libio/tst-cleanup-default.c                |  1 +
  libio/tst-cleanup-nostart-stop-gc-static.c |  1 +
  libio/tst-cleanup-nostart-stop-gc.c        |  1 +
  libio/tst-cleanup-start-stop-gc-static.c   |  1 +
  libio/tst-cleanup-start-stop-gc.c          |  1 +
  libio/tst-cleanup.c                        | 34 +++++++++++++
  libio/tst-cleanup.exp                      |  1 +
  13 files changed, 162 insertions(+), 4 deletions(-)
  create mode 100644 libio/tst-cleanup-default-static.c
  create mode 100644 libio/tst-cleanup-default.c
  create mode 100644 libio/tst-cleanup-nostart-stop-gc-static.c
  create mode 100644 libio/tst-cleanup-nostart-stop-gc.c
  create mode 100644 libio/tst-cleanup-start-stop-gc-static.c
  create mode 100644 libio/tst-cleanup-start-stop-gc.c
  create mode 100644 libio/tst-cleanup.c
  create mode 100644 libio/tst-cleanup.exp

diff --git a/config.h.in b/config.h.in
index ca1547ae67..96a08c7757 100644
--- a/config.h.in
+++ b/config.h.in
@@ -187,6 +187,9 @@
  /* Define if gcc supports attribute ifunc.  */
  #undef HAVE_GCC_IFUNC
  
+/* Define if CC supports attribute retain.  */
+#undef HAVE_GNU_RETAIN
+
  /* Define if the linker defines __ehdr_start.  */
  #undef HAVE_EHDR_START
  
diff --git a/configure b/configure
index fcf43bf7de..e64b7f8efe 100755
--- a/configure
+++ b/configure
@@ -4105,6 +4105,31 @@ fi
  $as_echo "$libc_cv_textrel_ifunc" >&6; }
  
  
+# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
+$as_echo_n "checking for GNU attribute retain support... " >&6; }
+if ${libc_cv_gnu_retain+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat > conftest.c <<EOF
+static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
+EOF
+libc_cv_gnu_retain=no
+if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
+   2>&5 ; then
+  libc_cv_gnu_retain=yes
+fi
+rm -f conftest*
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
+$as_echo "$libc_cv_gnu_retain" >&6; }
+if test $libc_cv_gnu_retain = yes; then
+  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
+
+fi
+config_vars="$config_vars
+have-gnu-retain = $libc_cv_gnu_retain"
+
  # Check if gcc warns about alias for function with incompatible types.
  { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
  $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
@@ -5871,6 +5896,40 @@ fi
  $as_echo "$libc_linker_feature" >&6; }
  
  
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
+$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
+  if test -n "$libc_linker_check"; then
+    cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+				-Wl,-z,start-stop-gc -nostdlib -nostartfiles
+				-fPIC -shared -o conftest.so conftest.c
+				1>&5'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; }
+    then
+      libc_linker_feature=yes
+    fi
+    rm -f conftest*
+  fi
+fi
+if test $libc_linker_feature = yes; then
+  libc_cv_z_start_stop_gc=yes
+else
+  libc_cv_z_start_stop_gc=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
+
  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
  libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index fce967f2c2..cc47e56e82 100644
--- a/configure.ac
+++ b/configure.ac
@@ -707,6 +707,23 @@ fi
  rm -f conftest*])
  AC_SUBST(libc_cv_textrel_ifunc)
  
+# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
+AC_CACHE_CHECK([for GNU attribute retain support],
+	       libc_cv_gnu_retain, [dnl
+cat > conftest.c <<EOF
+static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
+EOF
+libc_cv_gnu_retain=no
+if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
+   2>&AS_MESSAGE_LOG_FD ; then
+  libc_cv_gnu_retain=yes
+fi
+rm -f conftest*])
+if test $libc_cv_gnu_retain = yes; then
+  AC_DEFINE(HAVE_GNU_RETAIN)
+fi
+LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
+
  # Check if gcc warns about alias for function with incompatible types.
  AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
  	       libc_cv_gcc_incompatible_alias, [dnl
@@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
  		    [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
  AC_SUBST(libc_cv_z_execstack)
  
+LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
+		    [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
+LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
+
  LIBC_LINKER_FEATURE([--no-dynamic-linker],
  		    [-Wl,--no-dynamic-linker],
  		    [libc_cv_no_dynamic_linker=yes],
diff --git a/include/libc-symbols.h b/include/libc-symbols.h
index 546fc26a7b..127ea656c2 100644
--- a/include/libc-symbols.h
+++ b/include/libc-symbols.h
@@ -352,6 +352,12 @@ for linking")
  
  */
  
+#ifdef HAVE_GNU_RETAIN
+# define attribute_used_retain __attribute__ ((__used__, __retain__))
+#else
+# define attribute_used_retain __attribute__ ((__used__))
+#endif
+
  /* Symbol set support macros.  */
  
  /* Make SYMBOL, which is in the text segment, an element of SET.  */
@@ -367,12 +373,12 @@ for linking")
  /* When building a shared library, make the set section writable,
     because it will need to be relocated at run time anyway.  */
  # define _elf_set_element(set, symbol) \
-  static const void *__elf_set_##set##_element_##symbol##__ \
-    __attribute__ ((used, section (#set))) = &(symbol)
+    static const void *__elf_set_##set##_element_##symbol##__ \
+      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
  #else
  # define _elf_set_element(set, symbol) \
-  static const void *const __elf_set_##set##_element_##symbol##__ \
-    __attribute__ ((used, section (#set))) = &(symbol)
+    static const void *const __elf_set_##set##_element_##symbol##__ \
+      attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
  #endif
  
  /* Define SET as a symbol set.  This may be required (it is in a.out) to
diff --git a/libio/Makefile b/libio/Makefile
index 12ce41038f..ed0ce4ee81 100644
--- a/libio/Makefile
+++ b/libio/Makefile
@@ -195,6 +195,26 @@ ifeq (yes,$(build-shared))
  tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
  		 $(objpfx)tst-bz24228-mem.out
  endif
+
+tests += tst-cleanup-default tst-cleanup-default-static
+tests-static += tst-cleanup-default-static
+tests-special += $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-cleanup-default-static-cmp.out
+LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
+LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
+
+ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
+tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
+		tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
+tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
+tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
+		$(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
+		$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
+		$(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
+LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
+LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
+LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
+LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
+endif
  endif
  
  include ../Rules
@@ -224,6 +244,14 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
  $(objpfx)tst-wfile-sync.out: $(gen-locales)
  endif
  
+define gen-tst-cleanup
+$(objpfx)tst-cleanup-$1-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-$1.out
+	cmp $$^ > $$@; $$(evaluate-test)
+endef
+
+$(foreach t,default default-static start-stop-gc start-stop-gc-static nostart-stop-gc nostart-stop-gc-static, \
+  $(eval $(call gen-tst-cleanup,$(t))))
+
  $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
  	$(SHELL) $< $(common-objpfx) '$(test-program-prefix)'	\
  	$(common-objpfx)libio/; \
diff --git a/libio/tst-cleanup-default-static.c b/libio/tst-cleanup-default-static.c
new file mode 100644
index 0000000000..c39956e2a8
--- /dev/null
+++ b/libio/tst-cleanup-default-static.c
@@ -0,0 +1 @@
+#include "tst-cleanup.c"
diff --git a/libio/tst-cleanup-default.c b/libio/tst-cleanup-default.c
new file mode 100644
index 0000000000..c39956e2a8
--- /dev/null
+++ b/libio/tst-cleanup-default.c
@@ -0,0 +1 @@
+#include "tst-cleanup.c"
diff --git a/libio/tst-cleanup-nostart-stop-gc-static.c b/libio/tst-cleanup-nostart-stop-gc-static.c
new file mode 100644
index 0000000000..c39956e2a8
--- /dev/null
+++ b/libio/tst-cleanup-nostart-stop-gc-static.c
@@ -0,0 +1 @@
+#include "tst-cleanup.c"
diff --git a/libio/tst-cleanup-nostart-stop-gc.c b/libio/tst-cleanup-nostart-stop-gc.c
new file mode 100644
index 0000000000..c39956e2a8
--- /dev/null
+++ b/libio/tst-cleanup-nostart-stop-gc.c
@@ -0,0 +1 @@
+#include "tst-cleanup.c"
diff --git a/libio/tst-cleanup-start-stop-gc-static.c b/libio/tst-cleanup-start-stop-gc-static.c
new file mode 100644
index 0000000000..c39956e2a8
--- /dev/null
+++ b/libio/tst-cleanup-start-stop-gc-static.c
@@ -0,0 +1 @@
+#include "tst-cleanup.c"
diff --git a/libio/tst-cleanup-start-stop-gc.c b/libio/tst-cleanup-start-stop-gc.c
new file mode 100644
index 0000000000..c39956e2a8
--- /dev/null
+++ b/libio/tst-cleanup-start-stop-gc.c
@@ -0,0 +1 @@
+#include "tst-cleanup.c"
diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
new file mode 100644
index 0000000000..837feac164
--- /dev/null
+++ b/libio/tst-cleanup.c
@@ -0,0 +1,34 @@
+/* Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* Test that stdout is flushed after atexit callbacks were run, even if the
+ * executable is linked with --gc-sections.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+void
+hook (void)
+{
+  puts ("hello");
+}
+
+int
+main (void)
+{
+  atexit (hook);
+}
diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
new file mode 100644
index 0000000000..ce01362503
--- /dev/null
+++ b/libio/tst-cleanup.exp
@@ -0,0 +1 @@
+hello