[v4] Set the retain attribute on _elf_set_element if CC supports [BZ #27492]
Commit Message
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
---
config.h.in | 3 +++
configure | 58 ++++++++++++++++++++++++++++++++++++++++++
configure.ac | 20 +++++++++++++++
include/libc-symbols.h | 14 +++++++---
libio/Makefile | 32 +++++++++++++++++++++++
libio/tst-cleanup.c | 33 ++++++++++++++++++++++++
libio/tst-cleanup.exp | 1 +
7 files changed, 157 insertions(+), 4 deletions(-)
create mode 100644 libio/tst-cleanup.c
create mode 100644 libio/tst-cleanup.exp
Comments
On Wed, Mar 31, 2021 at 12:39 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
> ---
> config.h.in | 3 +++
> configure | 58 ++++++++++++++++++++++++++++++++++++++++++
> configure.ac | 20 +++++++++++++++
> include/libc-symbols.h | 14 +++++++---
> libio/Makefile | 32 +++++++++++++++++++++++
> libio/tst-cleanup.c | 33 ++++++++++++++++++++++++
> libio/tst-cleanup.exp | 1 +
> 7 files changed, 157 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..95af1ef229 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 gcc supports attribute retain. */
> +#undef HAVE_GCC_RETAIN
> +
> /* Define if the linker defines __ehdr_start. */
> #undef HAVE_EHDR_START
>
> diff --git a/configure b/configure
> index fcf43bf7de..fa86348342 100755
> --- a/configure
> +++ b/configure
> @@ -626,6 +626,7 @@ fno_unit_at_a_time
> libc_cv_has_glob_dat
> libc_cv_hashstyle
> libc_cv_fpie
> +libc_cv_z_start_stop_gc
> libc_cv_z_execstack
> libc_cv_z_combreloc
> ASFLAGS_config
> @@ -4105,6 +4106,29 @@ fi
> $as_echo "$libc_cv_textrel_ifunc" >&6; }
>
>
> +# Check if gcc supports attribute retain as it is used in attribute_used_retain macro.
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for gcc attribute retain support" >&5
> +$as_echo_n "checking for gcc attribute retain support... " >&6; }
> +if ${libc_cv_gcc_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_gcc_retain=no
> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> + 2>&5 ; then
> + libc_cv_gcc_retain=yes
> +fi
> +rm -f conftest*
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gcc_retain" >&5
> +$as_echo "$libc_cv_gcc_retain" >&6; }
> +if test $libc_cv_gcc_retain = yes; then
> + $as_echo "#define HAVE_GCC_RETAIN 1" >>confdefs.h
> +
> +fi
> +
> # 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 +5895,40 @@ 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..4e2907da92 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -707,6 +707,22 @@ fi
> rm -f conftest*])
> AC_SUBST(libc_cv_textrel_ifunc)
>
> +# Check if gcc supports attribute retain as it is used in attribute_used_retain macro.
> +AC_CACHE_CHECK([for gcc attribute retain support],
> + libc_cv_gcc_retain, [dnl
> +cat > conftest.c <<EOF
> +static int var __attribute__ ((used, retain, section ("__libc_atexit")));
> +EOF
> +libc_cv_gcc_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_gcc_retain=yes
> +fi
> +rm -f conftest*])
> +if test $libc_cv_gcc_retain = yes; then
> + AC_DEFINE(HAVE_GCC_RETAIN)
> +fi
> +
> # Check if gcc warns about alias for function with incompatible types.
> AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
> libc_cv_gcc_incompatible_alias, [dnl
> @@ -1317,6 +1333,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
> [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
> AC_SUBST(libc_cv_z_execstack)
>
> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> + [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$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..b311c90f0c 100644
> --- a/include/libc-symbols.h
> +++ b/include/libc-symbols.h
> @@ -352,6 +352,12 @@ for linking")
>
> */
>
> +#ifdef HAVE_GCC_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..439d22e057 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 += $(objpfx)tst-cleanup-default-cmp.out
> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> +
> +ifeq ($(have-z-start-stop-gc),yes)
> +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
> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
Won't this test fail if linker supports -z start-stop-gc and GCC doesn't support
retain attribute?
> +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 @@
> +/* 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 2021-03-31, H.J. Lu wrote:
>On Wed, Mar 31, 2021 at 12:39 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
>> ---
>> config.h.in | 3 +++
>> configure | 58 ++++++++++++++++++++++++++++++++++++++++++
>> configure.ac | 20 +++++++++++++++
>> include/libc-symbols.h | 14 +++++++---
>> libio/Makefile | 32 +++++++++++++++++++++++
>> libio/tst-cleanup.c | 33 ++++++++++++++++++++++++
>> libio/tst-cleanup.exp | 1 +
>> 7 files changed, 157 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..95af1ef229 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 gcc supports attribute retain. */
>> +#undef HAVE_GCC_RETAIN
>> +
>> /* Define if the linker defines __ehdr_start. */
>> #undef HAVE_EHDR_START
>>
>> diff --git a/configure b/configure
>> index fcf43bf7de..fa86348342 100755
>> --- a/configure
>> +++ b/configure
>> @@ -626,6 +626,7 @@ fno_unit_at_a_time
>> libc_cv_has_glob_dat
>> libc_cv_hashstyle
>> libc_cv_fpie
>> +libc_cv_z_start_stop_gc
>> libc_cv_z_execstack
>> libc_cv_z_combreloc
>> ASFLAGS_config
>> @@ -4105,6 +4106,29 @@ fi
>> $as_echo "$libc_cv_textrel_ifunc" >&6; }
>>
>>
>> +# Check if gcc supports attribute retain as it is used in attribute_used_retain macro.
>> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for gcc attribute retain support" >&5
>> +$as_echo_n "checking for gcc attribute retain support... " >&6; }
>> +if ${libc_cv_gcc_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_gcc_retain=no
>> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
>> + 2>&5 ; then
>> + libc_cv_gcc_retain=yes
>> +fi
>> +rm -f conftest*
>> +fi
>> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gcc_retain" >&5
>> +$as_echo "$libc_cv_gcc_retain" >&6; }
>> +if test $libc_cv_gcc_retain = yes; then
>> + $as_echo "#define HAVE_GCC_RETAIN 1" >>confdefs.h
>> +
>> +fi
>> +
>> # 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 +5895,40 @@ 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..4e2907da92 100644
>> --- a/configure.ac
>> +++ b/configure.ac
>> @@ -707,6 +707,22 @@ fi
>> rm -f conftest*])
>> AC_SUBST(libc_cv_textrel_ifunc)
>>
>> +# Check if gcc supports attribute retain as it is used in attribute_used_retain macro.
>> +AC_CACHE_CHECK([for gcc attribute retain support],
>> + libc_cv_gcc_retain, [dnl
>> +cat > conftest.c <<EOF
>> +static int var __attribute__ ((used, retain, section ("__libc_atexit")));
>> +EOF
>> +libc_cv_gcc_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_gcc_retain=yes
>> +fi
>> +rm -f conftest*])
>> +if test $libc_cv_gcc_retain = yes; then
>> + AC_DEFINE(HAVE_GCC_RETAIN)
>> +fi
>> +
>> # Check if gcc warns about alias for function with incompatible types.
>> AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
>> libc_cv_gcc_incompatible_alias, [dnl
>> @@ -1317,6 +1333,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
>> [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
>> AC_SUBST(libc_cv_z_execstack)
>>
>> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
>> + [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
>> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$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..b311c90f0c 100644
>> --- a/include/libc-symbols.h
>> +++ b/include/libc-symbols.h
>> @@ -352,6 +352,12 @@ for linking")
>>
>> */
>>
>> +#ifdef HAVE_GCC_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..439d22e057 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 += $(objpfx)tst-cleanup-default-cmp.out
>> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
>> +
>> +ifeq ($(have-z-start-stop-gc),yes)
>> +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 \
>> + $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
>> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
>
>Won't this test fail if linker supports -z start-stop-gc and GCC doesn't support
>retain attribute?
Yes, but that doesn't happen in practice. If ld supports -z start-stop-gc,
the GNU as should be new and the GCC should support 'retain'.
But perhaps it is good to prevent the issue, I can change
+ifeq ($(have-z-start-stop-gc),yes)
to
+ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
and add a LIBC_CONFIG_VAR in configure.ac.
>> +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 @@
>> +/* 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
>>
>
>
>--
>H.J.
On Wed, Mar 31, 2021 at 5:02 PM Fangrui Song <maskray@google.com> wrote:
>
> On 2021-03-31, H.J. Lu wrote:
> >On Wed, Mar 31, 2021 at 12:39 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
> >> ---
> >> config.h.in | 3 +++
> >> configure | 58 ++++++++++++++++++++++++++++++++++++++++++
> >> configure.ac | 20 +++++++++++++++
> >> include/libc-symbols.h | 14 +++++++---
> >> libio/Makefile | 32 +++++++++++++++++++++++
> >> libio/tst-cleanup.c | 33 ++++++++++++++++++++++++
> >> libio/tst-cleanup.exp | 1 +
> >> 7 files changed, 157 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..95af1ef229 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 gcc supports attribute retain. */
> >> +#undef HAVE_GCC_RETAIN
> >> +
> >> /* Define if the linker defines __ehdr_start. */
> >> #undef HAVE_EHDR_START
> >>
> >> diff --git a/configure b/configure
> >> index fcf43bf7de..fa86348342 100755
> >> --- a/configure
> >> +++ b/configure
> >> @@ -626,6 +626,7 @@ fno_unit_at_a_time
> >> libc_cv_has_glob_dat
> >> libc_cv_hashstyle
> >> libc_cv_fpie
> >> +libc_cv_z_start_stop_gc
> >> libc_cv_z_execstack
> >> libc_cv_z_combreloc
> >> ASFLAGS_config
> >> @@ -4105,6 +4106,29 @@ fi
> >> $as_echo "$libc_cv_textrel_ifunc" >&6; }
> >>
> >>
> >> +# Check if gcc supports attribute retain as it is used in attribute_used_retain macro.
> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for gcc attribute retain support" >&5
> >> +$as_echo_n "checking for gcc attribute retain support... " >&6; }
> >> +if ${libc_cv_gcc_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_gcc_retain=no
> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> >> + 2>&5 ; then
> >> + libc_cv_gcc_retain=yes
> >> +fi
> >> +rm -f conftest*
> >> +fi
> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gcc_retain" >&5
> >> +$as_echo "$libc_cv_gcc_retain" >&6; }
> >> +if test $libc_cv_gcc_retain = yes; then
> >> + $as_echo "#define HAVE_GCC_RETAIN 1" >>confdefs.h
> >> +
> >> +fi
> >> +
> >> # 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 +5895,40 @@ 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..4e2907da92 100644
> >> --- a/configure.ac
> >> +++ b/configure.ac
> >> @@ -707,6 +707,22 @@ fi
> >> rm -f conftest*])
> >> AC_SUBST(libc_cv_textrel_ifunc)
> >>
> >> +# Check if gcc supports attribute retain as it is used in attribute_used_retain macro.
> >> +AC_CACHE_CHECK([for gcc attribute retain support],
> >> + libc_cv_gcc_retain, [dnl
> >> +cat > conftest.c <<EOF
> >> +static int var __attribute__ ((used, retain, section ("__libc_atexit")));
> >> +EOF
> >> +libc_cv_gcc_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_gcc_retain=yes
> >> +fi
> >> +rm -f conftest*])
> >> +if test $libc_cv_gcc_retain = yes; then
> >> + AC_DEFINE(HAVE_GCC_RETAIN)
> >> +fi
> >> +
> >> # Check if gcc warns about alias for function with incompatible types.
> >> AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
> >> libc_cv_gcc_incompatible_alias, [dnl
> >> @@ -1317,6 +1333,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
> >> [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
> >> AC_SUBST(libc_cv_z_execstack)
> >>
> >> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> >> + [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$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..b311c90f0c 100644
> >> --- a/include/libc-symbols.h
> >> +++ b/include/libc-symbols.h
> >> @@ -352,6 +352,12 @@ for linking")
> >>
> >> */
> >>
> >> +#ifdef HAVE_GCC_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..439d22e057 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 += $(objpfx)tst-cleanup-default-cmp.out
> >> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> >> +
> >> +ifeq ($(have-z-start-stop-gc),yes)
> >> +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 \
> >> + $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
> >> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
> >
> >Won't this test fail if linker supports -z start-stop-gc and GCC doesn't support
> >retain attribute?
>
> Yes, but that doesn't happen in practice. If ld supports -z start-stop-gc,
> the GNU as should be new and the GCC should support 'retain'.
I am using GCC 10 and binutils 2.37.
> But perhaps it is good to prevent the issue, I can change
>
> +ifeq ($(have-z-start-stop-gc),yes)
>
> to
>
> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
>
> and add a LIBC_CONFIG_VAR in configure.ac.
>
Yes, please.
Thanks.
@@ -187,6 +187,9 @@
/* Define if gcc supports attribute ifunc. */
#undef HAVE_GCC_IFUNC
+/* Define if gcc supports attribute retain. */
+#undef HAVE_GCC_RETAIN
+
/* Define if the linker defines __ehdr_start. */
#undef HAVE_EHDR_START
@@ -626,6 +626,7 @@ fno_unit_at_a_time
libc_cv_has_glob_dat
libc_cv_hashstyle
libc_cv_fpie
+libc_cv_z_start_stop_gc
libc_cv_z_execstack
libc_cv_z_combreloc
ASFLAGS_config
@@ -4105,6 +4106,29 @@ fi
$as_echo "$libc_cv_textrel_ifunc" >&6; }
+# Check if gcc supports attribute retain as it is used in attribute_used_retain macro.
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for gcc attribute retain support" >&5
+$as_echo_n "checking for gcc attribute retain support... " >&6; }
+if ${libc_cv_gcc_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_gcc_retain=no
+if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
+ 2>&5 ; then
+ libc_cv_gcc_retain=yes
+fi
+rm -f conftest*
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gcc_retain" >&5
+$as_echo "$libc_cv_gcc_retain" >&6; }
+if test $libc_cv_gcc_retain = yes; then
+ $as_echo "#define HAVE_GCC_RETAIN 1" >>confdefs.h
+
+fi
+
# 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 +5895,40 @@ 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
@@ -707,6 +707,22 @@ fi
rm -f conftest*])
AC_SUBST(libc_cv_textrel_ifunc)
+# Check if gcc supports attribute retain as it is used in attribute_used_retain macro.
+AC_CACHE_CHECK([for gcc attribute retain support],
+ libc_cv_gcc_retain, [dnl
+cat > conftest.c <<EOF
+static int var __attribute__ ((used, retain, section ("__libc_atexit")));
+EOF
+libc_cv_gcc_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_gcc_retain=yes
+fi
+rm -f conftest*])
+if test $libc_cv_gcc_retain = yes; then
+ AC_DEFINE(HAVE_GCC_RETAIN)
+fi
+
# Check if gcc warns about alias for function with incompatible types.
AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
libc_cv_gcc_incompatible_alias, [dnl
@@ -1317,6 +1333,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
[libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
AC_SUBST(libc_cv_z_execstack)
+LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
+ [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
+LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
@@ -352,6 +352,12 @@ for linking")
*/
+#ifdef HAVE_GCC_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
@@ -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 += $(objpfx)tst-cleanup-default-cmp.out
+LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
+
+ifeq ($(have-z-start-stop-gc),yes)
+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
+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/; \
new file mode 100644
@@ -0,0 +1,33 @@
+/* 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);
+}
new file mode 100644
@@ -0,0 +1 @@
+hello