[PATCH v5] Set the retain attribute on _elf_set_element if CC supports [BZ #27492]
Fangrui Song
maskray@google.com
Fri Apr 2 17:09:41 GMT 2021
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.
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