[RFC,v10,4/7] Add DT_GNU_FLAGS_1/DF_GNU_1_UNIQUE to glibc DSOs (bug 22745)

  libc.so, libpthread.so etc should have the new unique-dso-by-default
flag set to allow dlmopen to work better (libc et al instance shared
by default when DSOs dlmopened into a new namespace).
---
 Makeconfig                |  3 +++
 Makerules                 | 19 +++++++++++++-
 config.make.in            |  1 +
 configure                 | 54 ++++++++++++++++++++++++++++++++++++---
 configure.ac              | 32 +++++++++++++++++++++--
 dynamic-notes.c           |  4 +++
 elf/Makefile              |  3 +++
 extra-lib.mk              |  3 +++
 htl/Makefile              |  3 +++
 iconvdata/Makefile        |  3 +++
 iconvdata/extra-module.mk |  4 +++
 nptl/Makefile             |  3 +++
 12 files changed, 126 insertions(+), 6 deletions(-)
 create mode 100644 dynamic-notes.c
  

On 22/03/2021 12:41, Vivek Das Mohapatra via Libc-alpha wrote:
> libc.so, libpthread.so etc should have the new unique-dso-by-default
> flag set to allow dlmopen to work better (libc et al instance shared
> by default when DSOs dlmopened into a new namespace).

Some comments below.

> ---
>  Makeconfig                |  3 +++
>  Makerules                 | 19 +++++++++++++-
>  config.make.in            |  1 +
>  configure                 | 54 ++++++++++++++++++++++++++++++++++++---
>  configure.ac              | 32 +++++++++++++++++++++--
>  dynamic-notes.c           |  4 +++
>  elf/Makefile              |  3 +++
>  extra-lib.mk              |  3 +++
>  htl/Makefile              |  3 +++
>  iconvdata/Makefile        |  3 +++
>  iconvdata/extra-module.mk |  4 +++
>  nptl/Makefile             |  3 +++
>  12 files changed, 126 insertions(+), 6 deletions(-)
>  create mode 100644 dynamic-notes.c
> 
> diff --git a/Makeconfig b/Makeconfig
> index 01f8638c2e..7e1116163f 100644
> --- a/Makeconfig
> +++ b/Makeconfig
> @@ -398,6 +398,9 @@ LDFLAGS-lib.so += -Wl,-z,now
>  # Extra flags for dynamically linked non-test main programs.
>  link-extra-flags += -Wl,-z,now
>  endif
> +ifeq ($(ld-zunique),yes)
> +LDFLAGS-lib.so += -Wl,-z,unique
> +endif
>  
>  # Command to run after every final link (executable or shared object).
>  # This is invoked with $(call after-link,...), so it should operate on

Ok.

> diff --git a/Makerules b/Makerules
> index ca9885436e..d54767f3a6 100644
> --- a/Makerules
> +++ b/Makerules
> @@ -581,7 +581,8 @@ $(common-objpfx)shlib.lds: $(common-objpfx)config.make $(..)Makerules
>  		 PROVIDE(__start___libc_IO_vtables = .);\
>  		 __libc_IO_vtables : { *(__libc_IO_vtables) }\
>  		 PROVIDE(__stop___libc_IO_vtables = .);\
> -		 /DISCARD/ : { *(.gnu.glibc-stub.*) }@'
> +		 /DISCARD/ : { *(.gnu.glibc-stub.*) }@' \
> +	      -e 's/^.*\*(\.dynamic).*$$/   .dynamic : { *dynamic-notes.os(.dynamic) *(.dynamic) }/'
>  	test -s $@T
>  	mv -f $@T $@
>  common-generated += shlib.lds

Ok.

> @@ -636,6 +637,17 @@ build-shlib-objlist = $(build-module-helper-objlist) \
>  # Also omits crti.o and crtn.o, which we do not want
>  # since we define our own `.init' section specially.
>  LDFLAGS-c.so = -nostdlib -nostartfiles
> +
> +# The stub dynamic-notes.os should not have weak/undefined symbol magic in it.
> +# It's not really part of the internals, rather it is a vector for linker magic
> +# which we need when the linker isn't new enough:
> +%/dynamic-notes.os: CPPFLAGS += -UMODULE_NAME
> +%/dynamic-notes.os: dynamic-notes.c
> +
> +ifeq ($(ld-zunique),yes)
> +LDFLAGS-c.so += -Wl,-z,unique
> +endif
> +
>  # But we still want to link libc.so against $(libc.so-gnulib).
>  LDLIBS-c.so += $(libc.so-gnulib)
>  # Give libc.so an entry point and make it directly runnable itself.
> @@ -706,6 +718,11 @@ $(common-objpfx)linkobj/libc.so: $(common-objpfx)linkobj/libc_pic.a \
>  	$(build-shlib)
>  	$(call after-link,$@)
>  
> +ifneq ($(ld-zunique),yes)
> +$(common-objpfx)libc.so: $(common-objpfx)dynamic-notes.os
> +$(common-objpfx)linkobj/libc.so: $(common-objpfx)dynamic-notes.os
> +endif
> +
>  ifeq ($(build-shared),yes)
>  $(common-objpfx)libc.so: $(common-objpfx)libc.map
>  endif
> diff --git a/config.make.in b/config.make.in
> index 7f47f0caa4..c2d818681b 100644
> --- a/config.make.in
> +++ b/config.make.in
> @@ -72,6 +72,7 @@ have-cc-with-libunwind = @libc_cv_cc_with_libunwind@
>  fno-unit-at-a-time = @fno_unit_at_a_time@
>  bind-now = @bindnow@
>  have-hash-style = @libc_cv_hashstyle@
> +ld-zunique = @ld_zunique@
>  use-default-link = @use_default_link@
>  have-cxx-thread_local = @libc_cv_cxx_thread_local@
>  have-loop-to-function = @libc_cv_cc_loop_to_function@
> diff --git a/configure b/configure
> index 37cef37413..1040130d6c 100755
> --- a/configure
> +++ b/configure
> @@ -685,6 +685,7 @@ hardcoded_path_in_tests
>  enable_timezone_tools
>  extra_nonshared_cflags
>  use_default_link
> +ld_zunique
>  sysheaders
>  ac_ct_CXX
>  CXXFLAGS
> @@ -731,6 +732,7 @@ infodir
>  docdir
>  oldincludedir
>  includedir
> +runstatedir
>  localstatedir
>  sharedstatedir
>  sysconfdir

Although it being autogenerated by autoconf, the runstatedir should be added
in a different patch.  So I think it should be manually removed for now.

> @@ -843,6 +845,7 @@ datadir='${datarootdir}'
>  sysconfdir='${prefix}/etc'
>  sharedstatedir='${prefix}/com'
>  localstatedir='${prefix}/var'
> +runstatedir='${localstatedir}/run'
>  includedir='${prefix}/include'
>  oldincludedir='/usr/include'
>  docdir='${datarootdir}/doc/${PACKAGE_TARNAME}'
> @@ -1095,6 +1098,15 @@ do
>    | -silent | --silent | --silen | --sile | --sil)
>      silent=yes ;;
>  
> +  -runstatedir | --runstatedir | --runstatedi | --runstated \
> +  | --runstate | --runstat | --runsta | --runst | --runs \
> +  | --run | --ru | --r)
> +    ac_prev=runstatedir ;;
> +  -runstatedir=* | --runstatedir=* | --runstatedi=* | --runstated=* \
> +  | --runstate=* | --runstat=* | --runsta=* | --runst=* | --runs=* \
> +  | --run=* | --ru=* | --r=*)
> +    runstatedir=$ac_optarg ;;
> +
>    -sbindir | --sbindir | --sbindi | --sbind | --sbin | --sbi | --sb)
>      ac_prev=sbindir ;;
>    -sbindir=* | --sbindir=* | --sbindi=* | --sbind=* | --sbin=* \

Ditto.

> @@ -1232,7 +1244,7 @@ fi
>  for ac_var in	exec_prefix prefix bindir sbindir libexecdir datarootdir \
>  		datadir sysconfdir sharedstatedir localstatedir includedir \
>  		oldincludedir docdir infodir htmldir dvidir pdfdir psdir \
> -		libdir localedir mandir
> +		libdir localedir mandir runstatedir
>  do
>    eval ac_val=\$$ac_var
>    # Remove trailing slashes.
> @@ -1385,6 +1397,7 @@ Fine tuning of the installation directories:
>    --sysconfdir=DIR        read-only single-machine data [PREFIX/etc]
>    --sharedstatedir=DIR    modifiable architecture-independent data [PREFIX/com]
>    --localstatedir=DIR     modifiable single-machine data [PREFIX/var]
> +  --runstatedir=DIR       modifiable per-process data [LOCALSTATEDIR/run]
>    --libdir=DIR            object code libraries [EPREFIX/lib]
>    --includedir=DIR        C header files [PREFIX/include]
>    --oldincludedir=DIR     C header files for non-gcc [/usr/include]
> @@ -3331,6 +3344,7 @@ fi
>  
>  
>  
> +
>  # Check whether --with-default-link was given.
>  if test "${with_default_link+set}" = set; then :
>    withval=$with_default_link; use_default_link=$withval
> @@ -5976,6 +5990,34 @@ fi
>  $as_echo "$libc_cv_hashstyle" >&6; }
>  
>  
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker DT_GNU_FLAGS_1/ DF_GNU_1_UNIQUE support" >&5
> +$as_echo_n "checking for linker DT_GNU_FLAGS_1/ DF_GNU_1_UNIQUE support... " >&6; }
> +if ${libc_cv_ld_zunique+:} false; then :
> +  $as_echo_n "(cached) " >&6
> +else
> +  cat > conftest.ld.c <<\EOF
> +int x (void) { return 0; }
> +EOF
> +libc_cv_ld_zunique=no;
> +if { ac_try='${CC-cc} -Wl,--fatal-warnings -Wl,-z,unique -shared -o conftest.ld.so conftest.ld.c'
> +  { { 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 $ac_status = 0; }; }
> +then
> +  libc_cv_ld_zunique=yes
> +else
> +  echo >&5 "\
> +${CC-cc} does not support -Wl,-z,unique from:
> +$ac_try"
> +fi;
> +ld_zunique=$libc_cv_ld_zunique
> +rm -f conftest*
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_ld_zunique" >&5
> +$as_echo "$libc_cv_ld_zunique" >&6; }
> +
>  # The linker's default -shared behavior is good enough if it
>  # does these things that our custom linker scripts ensure that
>  # all allocated NOTE sections come first.
> @@ -6021,10 +6063,16 @@ EOF
>        esac
>        shift 2
>      done
> -    case "$libc_seen_a$libc_seen_b" in
> -    yesyes)
> +    case "$libc_seen_a$libc_seen_b$libc_cv_ld_zunique" in
> +    yesyesyes)
>        libc_cv_use_default_link=yes
>        ;;
> +    yesyesno)
> +      echo >&5 "\
> +shared layout from:
> +$ac_try
> +is OK but -Wl,-z,unique is unsupported anyway"
> +      ;;
>      *)
>        echo >&5 "\
>  $libc_seen_a$libc_seen_b from:
> diff --git a/configure.ac b/configure.ac
> index 16b15b6f90..178874aa12 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -148,6 +148,7 @@ AC_ARG_WITH([headers],
>  	    [sysheaders=''])
>  AC_SUBST(sysheaders)
>  
> +AC_SUBST(ld_zunique)

Move it to where it is actually set below.

>  AC_SUBST(use_default_link)
>  AC_ARG_WITH([default-link],
>  	    AS_HELP_STRING([--with-default-link],
> @@ -1352,6 +1353,27 @@ fi
>  rm -f conftest*])
>  AC_SUBST(libc_cv_hashstyle)
>  
> +AC_CACHE_CHECK([for linker DT_GNU_FLAGS_1/ DF_GNU_1_UNIQUE support],
> +                libc_cv_ld_zunique, [dnl
> +cat > conftest.ld.c <<\EOF
> +int x (void) { return 0; }
> +EOF
> +libc_cv_ld_zunique=no;

Move it to the else below, as other tests do.

> +dnl FIXME FIXME FIXME FIXME FIXME FIXME FIXME FIXME FIXME FIXME FIXME FIXME
> +dnl THIS IS DELIBERATELY WRONG SO WE CAN TEST BUILDING WITH A TOO-OLD LINKER
> +dnl FIXME FIXME FIXME FIXME FIXME FIXME FIXME FIXME FIXME FIXME FIXME FIXME

I think this is leftover from development.

> +if AC_TRY_COMMAND([dnl
> +${CC-cc} -Wl,--fatal-warnings -Wl,-z,unique -shared -o conftest.ld.so conftest.ld.c])
> +then
> +  libc_cv_ld_zunique=yes
> +else
> +  echo >&AS_MESSAGE_LOG_FD "\
> +${CC-cc} does not support -Wl,-z,unique from:
> +$ac_try"
> +fi;
> +ld_zunique=$libc_cv_ld_zunique
> +rm -f conftest*])
> +
>  # The linker's default -shared behavior is good enough if it
>  # does these things that our custom linker scripts ensure that
>  # all allocated NOTE sections come first.
> @@ -1390,10 +1412,16 @@ EOF
>        esac
>        shift 2
>      done
> -    case "$libc_seen_a$libc_seen_b" in
> -    yesyes)
> +    case "$libc_seen_a$libc_seen_b$libc_cv_ld_zunique" in
> +    yesyesyes)
>        libc_cv_use_default_link=yes
>        ;;
> +    yesyesno)
> +      echo >&AS_MESSAGE_LOG_FD "\
> +shared layout from:
> +$ac_try
> +is OK but -Wl,-z,unique is unsupported anyway"
> +      ;;
>      *)
>        echo >&AS_MESSAGE_LOG_FD "\
>  $libc_seen_a$libc_seen_b from:

I am not sure this message here add much extra diagnosit .

> diff --git a/dynamic-notes.c b/dynamic-notes.c
> new file mode 100644
> index 0000000000..d0b487e970
> --- /dev/null
> +++ b/dynamic-notes.c
> @@ -0,0 +1,4 @@
> +#include <link.h>
> +
> +const ElfW(Dyn) __dynamic_note __attribute__ ((section (".dynamic"))) =
> +  { .d_tag = DT_GNU_FLAGS_1, .d_un.d_val = DF_GNU_1_UNIQUE };

I think we should put the note on the elf directory, even though it
is used on mutiples modules.

> diff --git a/elf/Makefile b/elf/Makefile
> index 3b8e13e066..22f2a87fcb 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -102,6 +102,9 @@ endif
>  
>  ifeq (yes,$(build-shared))
>  extra-objs	= $(all-rtld-routines:%=%.os) sofini.os interp.os
> +ifneq (yes,$(ld-zunique))
> +extra-objs      += ../dynamic-notes.os
> +endif
>  generated	+= librtld.os dl-allobjs.os ld.so ldd
>  install-others	= $(inst_rtlddir)/$(rtld-installed-name)
>  install-bin-script = ldd

Ok, although I think this implementation should be moved to elf/

> diff --git a/extra-lib.mk b/extra-lib.mk
> index 72f8d2e1df..4e4a447d5e 100644
> --- a/extra-lib.mk
> +++ b/extra-lib.mk
> @@ -101,6 +101,9 @@ $(objpfx)$(lib).so: $(firstword $($(lib)-map) \
>  				$(addprefix $(common-objpfx), \
>  					    $(filter $(lib).map, \
>  						     $(version-maps))))
> +ifneq ($(ld-zunique),yes)
> +$(objpfx)$(lib).so: $(common-objpfx)dynamic-notes.os
> +endif
>  endif
>  
>  endif

Ditto.

> diff --git a/htl/Makefile b/htl/Makefile
> index 895a6f777c..65ddd202a1 100644
> --- a/htl/Makefile
> +++ b/htl/Makefile
> @@ -205,6 +205,9 @@ libc-link.so = $(common-objpfx)libc.so
>  
>  extra-B-pthread.so = -B$(common-objpfx)htl/
>  LDFLAGS-pthread.so = -Wl,--enable-new-dtags,-z,nodelete,-z,initfirst
> +ifeq ($(ld-zunique),yes)
> +LDFLAGS-pthread.so += -Wl,-z,unique
> +endif
>  
>  include ../Rules
>  

Ok.

> diff --git a/iconvdata/Makefile b/iconvdata/Makefile
> index 55c527a5f7..2fe2404ade 100644
> --- a/iconvdata/Makefile
> +++ b/iconvdata/Makefile
> @@ -67,6 +67,9 @@ modules	:= ISO8859-1 ISO8859-2 ISO8859-3 ISO8859-4 ISO8859-5		 \
>  ifeq ($(bind-now),yes)
>  LDFLAGS.so += -Wl,-z,now
>  endif
> +ifeq ($(ld-zunique),yes)
> +LDFLAGS.so += -Wl,-z,unique
> +endif
>  
>  modules.so := $(addsuffix .so, $(modules))
>  

Ok, it does make sense to make the iconvdata unique.

> diff --git a/iconvdata/extra-module.mk b/iconvdata/extra-module.mk
> index ecaf507624..4d81358f19 100644
> --- a/iconvdata/extra-module.mk
> +++ b/iconvdata/extra-module.mk
> @@ -7,6 +7,10 @@ $(objpfx)$(mod).so: $(addprefix $(objpfx),$(addsuffix .os,$($(mod)-routines)))\
>  		    $(shlib-lds) $(link-libc-deps)
>  	$(build-module-asneeded)
>  
> +ifneq ($(ld-zunique),yes)
> +$(objpfx)$(mod).so: $(common-objpfx)dynamic-notes.os
> +endif
> +
>  ifneq (,$(extra-modules-left))
>  include extra-module.mk
>  endif

Ok.

> diff --git a/nptl/Makefile b/nptl/Makefile
> index b1948cc47a..dedfe389c0 100644
> --- a/nptl/Makefile
> +++ b/nptl/Makefile
> @@ -396,6 +396,9 @@ tests-printers-libs := $(static-thread-library)
>  endif
>  
>  LDFLAGS-pthread.so = -Wl,--enable-new-dtags,-z,nodelete,-z,initfirst
> +ifeq ($(ld-zunique),yes)
> +LDFLAGS-pthread.so += -Wl,-z,unique
> +endif
>  
>  tests += tst-cancelx7 tst-cancelx17 tst-cleanupx4
>  
> 

With the libpthread symbol move I think there is no need to add 'unique'
on libpthread.so anylonger.
  

> On 22/03/2021 12:41, Vivek Das Mohapatra via Libc-alpha wrote:

>> @@ -636,6 +637,17 @@ build-shlib-objlist = $(build-module-helper-objlist) \
>>  # Also omits crti.o and crtn.o, which we do not want
>>  # since we define our own `.init' section specially.
>>  LDFLAGS-c.so = -nostdlib -nostartfiles
>> +
>> +# The stub dynamic-notes.os should not have weak/undefined symbol magic in it.
>> +# It's not really part of the internals, rather it is a vector for linker magic
>> +# which we need when the linker isn't new enough:
>> +%/dynamic-notes.os: CPPFLAGS += -UMODULE_NAME

Although it seems correct to built it without defining MODULE_NAME, 
I wonder if there is a simpler way to define as MODULE_NAME=nonlib
(it seems be more correct than not defining any module name).

>> +%/dynamic-notes.os: dynamic-notes.c
I think this is not really required.
  

On Mai 28 2021, Adhemerval Zanella via Libc-alpha wrote:

> Although it being autogenerated by autoconf, the runstatedir should be added
> in a different patch.  So I think it should be manually removed for now.

That is the sign of a patched autoconf.  Only use a vanilla version.

Andreas.