Message ID | 20210329232440.3083493-1-maskray@google.com |
---|---|
State | New |
Headers | show |
Series | [v3] Set the retain attribute on _elf_set_element if CC supports [BZ #27492] | expand |
On Mon, Mar 29, 2021 at 4:24 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 > --- > config.h.in | 3 +++ > configure | 23 +++++++++++++++++++++++ > configure.ac | 16 ++++++++++++++++ > include/libc-symbols.h | 14 ++++++++++---- > 4 files changed, 52 insertions(+), 4 deletions(-) > > 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..6a6b8ac264 100755 > --- a/configure > +++ b/configure > @@ -4105,6 +4105,29 @@ fi > $as_echo "$libc_cv_textrel_ifunc" >&6; } > > > +# Check if gcc supports attribute ifunc as it is used in libc_ifunc 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; } > diff --git a/configure.ac b/configure.ac > index fce967f2c2..031b8c3fb3 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 ifunc as it is used in libc_ifunc 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 > 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 > -- > 2.31.0.291.g576ba9dcdaf-goog > Need gc-sections tests for linkers with and without -z start-stop-gc.
On Tue, Mar 30, 2021 at 11:17 AM H.J. Lu <hjl.tools@gmail.com> wrote: > > On Mon, Mar 29, 2021 at 4:24 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 > > --- > > config.h.in | 3 +++ > > configure | 23 +++++++++++++++++++++++ > > configure.ac | 16 ++++++++++++++++ > > include/libc-symbols.h | 14 ++++++++++---- > > 4 files changed, 52 insertions(+), 4 deletions(-) > > > > 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..6a6b8ac264 100755 > > --- a/configure > > +++ b/configure > > @@ -4105,6 +4105,29 @@ fi > > $as_echo "$libc_cv_textrel_ifunc" >&6; } > > > > > > +# Check if gcc supports attribute ifunc as it is used in libc_ifunc 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; } > > diff --git a/configure.ac b/configure.ac > > index fce967f2c2..031b8c3fb3 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 ifunc as it is used in libc_ifunc 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 > > 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 > > -- > > 2.31.0.291.g576ba9dcdaf-goog > > > > Need gc-sections tests for linkers with and without -z start-stop-gc. > > -- > H.J. I don't know how to add such a test... It needs to check flush at ext time but I cannot find a template in libio/tst-* ...
On Tue, Mar 30, 2021 at 12:17 PM Fāng-ruì Sòng <maskray@google.com> wrote: > > On Tue, Mar 30, 2021 at 11:17 AM H.J. Lu <hjl.tools@gmail.com> wrote: > > > > On Mon, Mar 29, 2021 at 4:24 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 > > > --- > > > config.h.in | 3 +++ > > > configure | 23 +++++++++++++++++++++++ > > > configure.ac | 16 ++++++++++++++++ > > > include/libc-symbols.h | 14 ++++++++++---- > > > 4 files changed, 52 insertions(+), 4 deletions(-) > > > > > > 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..6a6b8ac264 100755 > > > --- a/configure > > > +++ b/configure > > > @@ -4105,6 +4105,29 @@ fi > > > $as_echo "$libc_cv_textrel_ifunc" >&6; } > > > > > > > > > +# Check if gcc supports attribute ifunc as it is used in libc_ifunc 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; } > > > diff --git a/configure.ac b/configure.ac > > > index fce967f2c2..031b8c3fb3 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 ifunc as it is used in libc_ifunc 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 > > > 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 > > > -- > > > 2.31.0.291.g576ba9dcdaf-goog > > > > > > > Need gc-sections tests for linkers with and without -z start-stop-gc. > > > > -- > > H.J. > > I don't know how to add such a test... It needs to check flush at ext > time but I cannot find a template in libio/tst-* ... You can add a special rule to check for linker output with --print-gc-sections.
On 2021-03-30, H.J. Lu wrote: >On Tue, Mar 30, 2021 at 12:17 PM Fāng-ruì Sòng <maskray@google.com> wrote: >> >> On Tue, Mar 30, 2021 at 11:17 AM H.J. Lu <hjl.tools@gmail.com> wrote: >> > >> > On Mon, Mar 29, 2021 at 4:24 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 >> > > --- >> > > config.h.in | 3 +++ >> > > configure | 23 +++++++++++++++++++++++ >> > > configure.ac | 16 ++++++++++++++++ >> > > include/libc-symbols.h | 14 ++++++++++---- >> > > 4 files changed, 52 insertions(+), 4 deletions(-) >> > > >> > > 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..6a6b8ac264 100755 >> > > --- a/configure >> > > +++ b/configure >> > > @@ -4105,6 +4105,29 @@ fi >> > > $as_echo "$libc_cv_textrel_ifunc" >&6; } >> > > >> > > >> > > +# Check if gcc supports attribute ifunc as it is used in libc_ifunc 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; } >> > > diff --git a/configure.ac b/configure.ac >> > > index fce967f2c2..031b8c3fb3 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 ifunc as it is used in libc_ifunc 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 >> > > 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 >> > > -- >> > > 2.31.0.291.g576ba9dcdaf-goog >> > > >> > >> > Need gc-sections tests for linkers with and without -z start-stop-gc. >> > >> > -- >> > H.J. >> >> I don't know how to add such a test... It needs to check flush at ext >> time but I cannot find a template in libio/tst-* ... > >You can add a special rule to check for linker output with >--print-gc-sections. I can come up runtime tests. ( https://github.com/MaskRay/glibc/tree/retain) Runtime tests are direct. (Unsure how to test --print-gc-sections with tests-static...) diff --git a/libio/Makefile b/libio/Makefile index 12ce41038f..5e0e7f00cd 100644 --- a/libio/Makefile +++ b/libio/Makefile @@ -195,6 +195,13 @@ 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-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.out \ + $(objpfx)tst-cleanup-nostart-stop-gc.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 include ../Rules @@ -224,6 +231,20 @@ $(objpfx)tst_wprintf2.out: $(gen-locales) $(objpfx)tst-wfile-sync.out: $(gen-locales) endif +$(objpfx)tst-cleanup-start-stop-gc.out: $(objpfx)tst-cleanup-start-stop-gc + $< > $@T + grep hello $@T; $(evaluate-test) + rm -f $@T +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c + $(compile.c) -o $@ + +$(objpfx)tst-cleanup-nostart-stop-gc.out: $(objpfx)tst-cleanup-nostart-stop-gc + $< > $@T + grep hello $@T; $(evaluate-test) + rm -f $@T +$(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..de8130a482 --- /dev/null +++ b/libio/tst-cleanup.c @@ -0,0 +1,14 @@ +#include <stdio.h> +#include <stdlib.h> + +void +hook (void) +{ + puts ("hello"); +} + +int +main (void) +{ + atexit (hook); +}
On Tue, Mar 30, 2021 at 9:34 PM Fāng-ruì Sòng <maskray@google.com> wrote: > > On 2021-03-30, H.J. Lu wrote: > >On Tue, Mar 30, 2021 at 12:17 PM Fāng-ruì Sòng <maskray@google.com> wrote: > >> > >> On Tue, Mar 30, 2021 at 11:17 AM H.J. Lu <hjl.tools@gmail.com> wrote: > >> > > >> > On Mon, Mar 29, 2021 at 4:24 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 > >> > > --- > >> > > config.h.in | 3 +++ > >> > > configure | 23 +++++++++++++++++++++++ > >> > > configure.ac | 16 ++++++++++++++++ > >> > > include/libc-symbols.h | 14 ++++++++++---- > >> > > 4 files changed, 52 insertions(+), 4 deletions(-) > >> > > > >> > > 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..6a6b8ac264 100755 > >> > > --- a/configure > >> > > +++ b/configure > >> > > @@ -4105,6 +4105,29 @@ fi > >> > > $as_echo "$libc_cv_textrel_ifunc" >&6; } > >> > > > >> > > > >> > > +# Check if gcc supports attribute ifunc as it is used in libc_ifunc 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; } > >> > > diff --git a/configure.ac b/configure.ac > >> > > index fce967f2c2..031b8c3fb3 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 ifunc as it is used in libc_ifunc 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 > >> > > 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 > >> > > -- > >> > > 2.31.0.291.g576ba9dcdaf-goog > >> > > > >> > > >> > Need gc-sections tests for linkers with and without -z start-stop-gc. > >> > > >> > -- > >> > H.J. > >> > >> I don't know how to add such a test... It needs to check flush at ext > >> time but I cannot find a template in libio/tst-* ... > > > >You can add a special rule to check for linker output with > >--print-gc-sections. > > I can come up runtime tests. ( https://github.com/MaskRay/glibc/tree/retain) > Runtime tests are direct. > (Unsure how to test --print-gc-sections with tests-static...) > > > diff --git a/libio/Makefile b/libio/Makefile > index 12ce41038f..5e0e7f00cd 100644 > --- a/libio/Makefile > +++ b/libio/Makefile > @@ -195,6 +195,13 @@ 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-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.out \ > + $(objpfx)tst-cleanup-nostart-stop-gc.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 1. Need to check if linker supports -z start-stop-gc. 2. Need to test with only -Wl,--gc-sections. > endif > > include ../Rules > @@ -224,6 +231,20 @@ $(objpfx)tst_wprintf2.out: $(gen-locales) > $(objpfx)tst-wfile-sync.out: $(gen-locales) > endif > > +$(objpfx)tst-cleanup-start-stop-gc.out: $(objpfx)tst-cleanup-start-stop-gc > + $< > $@T > + grep hello $@T; $(evaluate-test) > + rm -f $@T tst-cleanup-start-stop-gc.out isn't generated. You should add a ".exp" file and compare the .out file against it. > +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c > + $(compile.c) -o $@ > + > +$(objpfx)tst-cleanup-nostart-stop-gc.out: $(objpfx)tst-cleanup-nostart-stop-gc > + $< > $@T > + grep hello $@T; $(evaluate-test) > + rm -f $@T > +$(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..de8130a482 > --- /dev/null > +++ b/libio/tst-cleanup.c > @@ -0,0 +1,14 @@ Missing comments and copyright notice. > +#include <stdio.h> > +#include <stdlib.h> > + > +void > +hook (void) > +{ > + puts ("hello"); > +} > + > +int > +main (void) > +{ > + atexit (hook); > +} -- H.J.
On 2021-03-31, H.J. Lu wrote: >On Tue, Mar 30, 2021 at 9:34 PM Fāng-ruì Sòng <maskray@google.com> wrote: >> >> On 2021-03-30, H.J. Lu wrote: >> >On Tue, Mar 30, 2021 at 12:17 PM Fāng-ruì Sòng <maskray@google.com> wrote: >> >> >> >> On Tue, Mar 30, 2021 at 11:17 AM H.J. Lu <hjl.tools@gmail.com> wrote: >> >> > >> >> > On Mon, Mar 29, 2021 at 4:24 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 >> >> > > --- >> >> > > config.h.in | 3 +++ >> >> > > configure | 23 +++++++++++++++++++++++ >> >> > > configure.ac | 16 ++++++++++++++++ >> >> > > include/libc-symbols.h | 14 ++++++++++---- >> >> > > 4 files changed, 52 insertions(+), 4 deletions(-) >> >> > > >> >> > > 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..6a6b8ac264 100755 >> >> > > --- a/configure >> >> > > +++ b/configure >> >> > > @@ -4105,6 +4105,29 @@ fi >> >> > > $as_echo "$libc_cv_textrel_ifunc" >&6; } >> >> > > >> >> > > >> >> > > +# Check if gcc supports attribute ifunc as it is used in libc_ifunc 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; } >> >> > > diff --git a/configure.ac b/configure.ac >> >> > > index fce967f2c2..031b8c3fb3 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 ifunc as it is used in libc_ifunc 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 >> >> > > 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 >> >> > > -- >> >> > > 2.31.0.291.g576ba9dcdaf-goog >> >> > > >> >> > >> >> > Need gc-sections tests for linkers with and without -z start-stop-gc. >> >> > >> >> > -- >> >> > H.J. >> >> >> >> I don't know how to add such a test... It needs to check flush at ext >> >> time but I cannot find a template in libio/tst-* ... >> > >> >You can add a special rule to check for linker output with >> >--print-gc-sections. >> >> I can come up runtime tests. ( https://github.com/MaskRay/glibc/tree/retain) >> Runtime tests are direct. >> (Unsure how to test --print-gc-sections with tests-static...) >> >> >> diff --git a/libio/Makefile b/libio/Makefile >> index 12ce41038f..5e0e7f00cd 100644 >> --- a/libio/Makefile >> +++ b/libio/Makefile >> @@ -195,6 +195,13 @@ 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-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.out \ >> + $(objpfx)tst-cleanup-nostart-stop-gc.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 > >1. Need to check if linker supports -z start-stop-gc. This seems difficult to do with Makefile... Second, do we need to check it? ld warns instead of errors for an unknown -z option, so not checking it may be fine. (GNU ld warns even with --fatal-warnings.) >2. Need to test with only -Wl,--gc-sections. OK, removed -z,nostart-stop-gc -LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections >> endif >> >> include ../Rules >> @@ -224,6 +231,20 @@ $(objpfx)tst_wprintf2.out: $(gen-locales) >> $(objpfx)tst-wfile-sync.out: $(gen-locales) >> endif >> >> +$(objpfx)tst-cleanup-start-stop-gc.out: $(objpfx)tst-cleanup-start-stop-gc >> + $< > $@T >> + grep hello $@T; $(evaluate-test) >> + rm -f $@T > >tst-cleanup-start-stop-gc.out isn't generated. You should add a ".exp" file >and compare the .out file against it. Thanks for the tip. Added tst-cleanup.exp with the content "hello\n" (see the usage below). > >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c >> + $(compile.c) -o $@ >> + >> +$(objpfx)tst-cleanup-nostart-stop-gc.out: $(objpfx)tst-cleanup-nostart-stop-gc >> + $< > $@T >> + grep hello $@T; $(evaluate-test) >> + rm -f $@T >> +$(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)' \ >> $(common-objpfx)libio/; \ >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c >> new file mode 100644 >> index 0000000000..de8130a482 >> --- /dev/null >> +++ b/libio/tst-cleanup.c >> @@ -0,0 +1,14 @@ > >Missing comments and copyright notice. OK. I find that many tst* files don't have a copyright notice.. Added. >> +#include <stdio.h> >> +#include <stdlib.h> >> + >> +void >> +hook (void) >> +{ >> + puts ("hello"); >> +} >> + >> +int >> +main (void) >> +{ >> + atexit (hook); >> +} diff --git a/libio/Makefile b/libio/Makefile index 12ce41038f..472a1e064c 100644 --- a/libio/Makefile +++ b/libio/Makefile @@ -195,6 +195,13 @@ ifeq (yes,$(build-shared)) tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \ $(objpfx)tst-bz24228-mem.out endif + +tests += tst-cleanup-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 include ../Rules @@ -224,6 +231,18 @@ $(objpfx)tst_wprintf2.out: $(gen-locales) $(objpfx)tst-wfile-sync.out: $(gen-locales) endif +$(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); +}
On Wed, Mar 31, 2021 at 11:09 AM Fāng-ruì Sòng <maskray@google.com> wrote: > > > On 2021-03-31, H.J. Lu wrote: > >On Tue, Mar 30, 2021 at 9:34 PM Fāng-ruì Sòng <maskray@google.com> wrote: > >> > >> On 2021-03-30, H.J. Lu wrote: > >> >On Tue, Mar 30, 2021 at 12:17 PM Fāng-ruì Sòng <maskray@google.com> wrote: > >> >> > >> >> On Tue, Mar 30, 2021 at 11:17 AM H.J. Lu <hjl.tools@gmail.com> wrote: > >> >> > > >> >> > On Mon, Mar 29, 2021 at 4:24 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 > >> >> > > --- > >> >> > > config.h.in | 3 +++ > >> >> > > configure | 23 +++++++++++++++++++++++ > >> >> > > configure.ac | 16 ++++++++++++++++ > >> >> > > include/libc-symbols.h | 14 ++++++++++---- > >> >> > > 4 files changed, 52 insertions(+), 4 deletions(-) > >> >> > > > >> >> > > 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..6a6b8ac264 100755 > >> >> > > --- a/configure > >> >> > > +++ b/configure > >> >> > > @@ -4105,6 +4105,29 @@ fi > >> >> > > $as_echo "$libc_cv_textrel_ifunc" >&6; } > >> >> > > > >> >> > > > >> >> > > +# Check if gcc supports attribute ifunc as it is used in libc_ifunc 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; } > >> >> > > diff --git a/configure.ac b/configure.ac > >> >> > > index fce967f2c2..031b8c3fb3 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 ifunc as it is used in libc_ifunc 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 > >> >> > > 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 > >> >> > > -- > >> >> > > 2.31.0.291.g576ba9dcdaf-goog > >> >> > > > >> >> > > >> >> > Need gc-sections tests for linkers with and without -z start-stop-gc. > >> >> > > >> >> > -- > >> >> > H.J. > >> >> > >> >> I don't know how to add such a test... It needs to check flush at ext > >> >> time but I cannot find a template in libio/tst-* ... > >> > > >> >You can add a special rule to check for linker output with > >> >--print-gc-sections. > >> > >> I can come up runtime tests. ( https://github.com/MaskRay/glibc/tree/retain) > >> Runtime tests are direct. > >> (Unsure how to test --print-gc-sections with tests-static...) > >> > >> > >> diff --git a/libio/Makefile b/libio/Makefile > >> index 12ce41038f..5e0e7f00cd 100644 > >> --- a/libio/Makefile > >> +++ b/libio/Makefile > >> @@ -195,6 +195,13 @@ 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-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.out \ > >> + $(objpfx)tst-cleanup-nostart-stop-gc.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 > > > >1. Need to check if linker supports -z start-stop-gc. > > This seems difficult to do with Makefile... Second, do we need to check it? > ld warns instead of errors for an unknown -z option, so not checking it > may be fine. (GNU ld warns even with --fatal-warnings.) Please use LIBC_LINKER_FEATURE and LIBC_CONFIG_VAR to detect and check linker features. > >2. Need to test with only -Wl,--gc-sections. > > OK, removed -z,nostart-stop-gc We need all 3 tests with -Wl,--gc-sections. > -LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc > +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections > > >> endif > >> > >> include ../Rules > >> @@ -224,6 +231,20 @@ $(objpfx)tst_wprintf2.out: $(gen-locales) > >> $(objpfx)tst-wfile-sync.out: $(gen-locales) > >> endif > >> > >> +$(objpfx)tst-cleanup-start-stop-gc.out: $(objpfx)tst-cleanup-start-stop-gc > >> + $< > $@T > >> + grep hello $@T; $(evaluate-test) > >> + rm -f $@T > > > >tst-cleanup-start-stop-gc.out isn't generated. You should add a ".exp" file > >and compare the .out file against it. > > Thanks for the tip. Added tst-cleanup.exp with the content "hello\n" (see the usage below). > > > >> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c > >> + $(compile.c) -o $@ > >> + > >> +$(objpfx)tst-cleanup-nostart-stop-gc.out: $(objpfx)tst-cleanup-nostart-stop-gc > >> + $< > $@T > >> + grep hello $@T; $(evaluate-test) > >> + rm -f $@T > >> +$(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)' \ > >> $(common-objpfx)libio/; \ > >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c > >> new file mode 100644 > >> index 0000000000..de8130a482 > >> --- /dev/null > >> +++ b/libio/tst-cleanup.c > >> @@ -0,0 +1,14 @@ > > > >Missing comments and copyright notice. > > OK. I find that many tst* files don't have a copyright notice.. > Added. > > >> +#include <stdio.h> > >> +#include <stdlib.h> > >> + > >> +void > >> +hook (void) > >> +{ > >> + puts ("hello"); > >> +} > >> + > >> +int > >> +main (void) > >> +{ > >> + atexit (hook); > >> +} > > > diff --git a/libio/Makefile b/libio/Makefile > index 12ce41038f..472a1e064c 100644 > --- a/libio/Makefile > +++ b/libio/Makefile > @@ -195,6 +195,13 @@ ifeq (yes,$(build-shared)) > tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \ > $(objpfx)tst-bz24228-mem.out > endif > + > +tests += tst-cleanup-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 > > include ../Rules > @@ -224,6 +231,18 @@ $(objpfx)tst_wprintf2.out: $(gen-locales) > $(objpfx)tst-wfile-sync.out: $(gen-locales) > endif > > +$(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/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..6a6b8ac264 100755 --- a/configure +++ b/configure @@ -4105,6 +4105,29 @@ fi $as_echo "$libc_cv_textrel_ifunc" >&6; } +# Check if gcc supports attribute ifunc as it is used in libc_ifunc 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; } diff --git a/configure.ac b/configure.ac index fce967f2c2..031b8c3fb3 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 ifunc as it is used in libc_ifunc 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 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