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

["H.J. Lu" <hjl.tools@gmail.com>]

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.


-- 
H.J.