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[v2] Set the retain attribute on _elf_set_element if CC supports [BZ #27492]

Message ID 20210322040044.2559211-1-maskray@google.com
State New
Headers show
Series [v2] Set the retain attribute on _elf_set_element if CC supports [BZ #27492] | expand

Commit Message

Fangrui Song March 22, 2021, 4 a.m. UTC 
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).
---
 config.h.in            |  3 +++
 configure              | 23 +++++++++++++++++++++++
 configure.ac           | 16 ++++++++++++++++
 include/libc-symbols.h | 30 +++++++++++++++++++++---------
 4 files changed, 63 insertions(+), 9 deletions(-)

Comments

H.J. Lu March 22, 2021, 4:24 a.m. UTC | #1 
On Sun, Mar 21, 2021 at 9:01 PM Fangrui Song via Libc-alpha
<libc-alpha@sourceware.org> 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).
> ---
>  config.h.in            |  3 +++
>  configure              | 23 +++++++++++++++++++++++
>  configure.ac           | 16 ++++++++++++++++
>  include/libc-symbols.h | 30 +++++++++++++++++++++---------
>  4 files changed, 63 insertions(+), 9 deletions(-)
>
> diff --git a/config.h.in b/config.h.in
> index f21bf04e47..cc875e90f9 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 37cef37413..28494de748 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 16b15b6f90..94ad713820 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 c83e550b03..f8eafcf1f3 100644
> --- a/include/libc-symbols.h
> +++ b/include/libc-symbols.h
> @@ -373,17 +373,29 @@ for linking")
>
>  /* These are all done the same way in ELF.
>     There is a new section created for each set.  */
> -#ifdef SHARED
> +#ifdef HAVE_GCC_RETAIN
> +# ifdef SHARED
>  /* 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)

You should define __attribute_used_and_retain__ instead.

> +  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, retain, section (#set))) = &(symbol)
> +# else
> +#  define _elf_set_element(set, symbol) \
> +     static const void *const __elf_set_##set##_element_##symbol##__ \
> +       __attribute__ ((used, retain, section (#set))) = &(symbol)
> +# endif
>  #else
> -# define _elf_set_element(set, symbol) \
> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> -    __attribute__ ((used, section (#set))) = &(symbol)
> -#endif
> +# ifdef SHARED
> +#  define _elf_set_element(set, symbol) \
> +     static const void *__elf_set_##set##_element_##symbol##__ \
> +       __attribute__ ((used, section (#set))) = &(symbol)
> +# else
> +#  define _elf_set_element(set, symbol) \
> +     static const void *const __elf_set_##set##_element_##symbol##__ \
> +       __attribute__ ((used, section (#set))) = &(symbol)
> +# endif
> +#endif /* HAVE_GCC_RETAIN  */
>
>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
>     be able to use the set's contents.  */
> --
> 2.31.0.rc2.261.g7f71774620-goog
>

libc.a is an installed file.  Does this work with older linkers?
Fangrui Song March 22, 2021, 4:40 a.m. UTC | #2 
On 2021-03-21, H.J. Lu wrote:
>On Sun, Mar 21, 2021 at 9:01 PM Fangrui Song via Libc-alpha
><libc-alpha@sourceware.org> 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).
>> ---
>>  config.h.in            |  3 +++
>>  configure              | 23 +++++++++++++++++++++++
>>  configure.ac           | 16 ++++++++++++++++
>>  include/libc-symbols.h | 30 +++++++++++++++++++++---------
>>  4 files changed, 63 insertions(+), 9 deletions(-)
>>
>> diff --git a/config.h.in b/config.h.in
>> index f21bf04e47..cc875e90f9 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 37cef37413..28494de748 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 16b15b6f90..94ad713820 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 c83e550b03..f8eafcf1f3 100644
>> --- a/include/libc-symbols.h
>> +++ b/include/libc-symbols.h
>> @@ -373,17 +373,29 @@ for linking")
>>
>>  /* These are all done the same way in ELF.
>>     There is a new section created for each set.  */
>> -#ifdef SHARED
>> +#ifdef HAVE_GCC_RETAIN
>> +# ifdef SHARED
>>  /* 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)
>
>You should define __attribute_used_and_retain__ instead.
>
>> +  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, retain, section (#set))) = &(symbol)
>> +# else
>> +#  define _elf_set_element(set, symbol) \
>> +     static const void *const __elf_set_##set##_element_##symbol##__ \
>> +       __attribute__ ((used, retain, section (#set))) = &(symbol)
>> +# endif
>>  #else
>> -# define _elf_set_element(set, symbol) \
>> -  static const void *const __elf_set_##set##_element_##symbol##__ \
>> -    __attribute__ ((used, section (#set))) = &(symbol)
>> -#endif
>> +# ifdef SHARED
>> +#  define _elf_set_element(set, symbol) \
>> +     static const void *__elf_set_##set##_element_##symbol##__ \
>> +       __attribute__ ((used, section (#set))) = &(symbol)
>> +# else
>> +#  define _elf_set_element(set, symbol) \
>> +     static const void *const __elf_set_##set##_element_##symbol##__ \
>> +       __attribute__ ((used, section (#set))) = &(symbol)
>> +# endif
>> +#endif /* HAVE_GCC_RETAIN  */
>>
>>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
>>     be able to use the set's contents.  */
>> --
>> 2.31.0.rc2.261.g7f71774620-goog
>>
>
>libc.a is an installed file.  Does this work with older linkers?
>
>-- 
>H.J.

How about 

   /* These are all done the same way in ELF.
      There is a new section created for each set.  */
   #ifdef HAVE_GCC_RETAIN
   # define attribute_used_retain_section(sec) \
       __attribute__ ((used, retain, section (sec)))
   #else
   # define attribute_used_retain_section(sec) \
       __attribute__ ((used, section (sec)))
   #endif
   #ifdef SHARED
   /* 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_retain_section(#set) = &(symbol)
   #else
   # define _elf_set_element(set, symbol) \
       static const void *const __elf_set_##set##_element_##symbol##__ \
         attribute_used_retain_section(#set) = &(symbol)
   #endif

? Yes, older linkers just ignore unknown section flags. That is the ELF spirit.
H.J. Lu March 22, 2021, 8:28 p.m. UTC | #3 
On Sun, Mar 21, 2021 at 9:40 PM Fangrui Song <maskray@google.com> wrote:
>
> On 2021-03-21, H.J. Lu wrote:
> >On Sun, Mar 21, 2021 at 9:01 PM Fangrui Song via Libc-alpha
> ><libc-alpha@sourceware.org> 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).
> >> ---
> >>  config.h.in            |  3 +++
> >>  configure              | 23 +++++++++++++++++++++++
> >>  configure.ac           | 16 ++++++++++++++++
> >>  include/libc-symbols.h | 30 +++++++++++++++++++++---------
> >>  4 files changed, 63 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/config.h.in b/config.h.in
> >> index f21bf04e47..cc875e90f9 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 37cef37413..28494de748 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 16b15b6f90..94ad713820 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 c83e550b03..f8eafcf1f3 100644
> >> --- a/include/libc-symbols.h
> >> +++ b/include/libc-symbols.h
> >> @@ -373,17 +373,29 @@ for linking")
> >>
> >>  /* These are all done the same way in ELF.
> >>     There is a new section created for each set.  */
> >> -#ifdef SHARED
> >> +#ifdef HAVE_GCC_RETAIN
> >> +# ifdef SHARED
> >>  /* 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)
> >
> >You should define __attribute_used_and_retain__ instead.
> >
> >> +  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, retain, section (#set))) = &(symbol)
> >> +# else
> >> +#  define _elf_set_element(set, symbol) \
> >> +     static const void *const __elf_set_##set##_element_##symbol##__ \
> >> +       __attribute__ ((used, retain, section (#set))) = &(symbol)
> >> +# endif
> >>  #else
> >> -# define _elf_set_element(set, symbol) \
> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> -#endif
> >> +# ifdef SHARED
> >> +#  define _elf_set_element(set, symbol) \
> >> +     static const void *__elf_set_##set##_element_##symbol##__ \
> >> +       __attribute__ ((used, section (#set))) = &(symbol)
> >> +# else
> >> +#  define _elf_set_element(set, symbol) \
> >> +     static const void *const __elf_set_##set##_element_##symbol##__ \
> >> +       __attribute__ ((used, section (#set))) = &(symbol)
> >> +# endif
> >> +#endif /* HAVE_GCC_RETAIN  */
> >>
> >>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
> >>     be able to use the set's contents.  */
> >> --
> >> 2.31.0.rc2.261.g7f71774620-goog
> >>
> >
> >libc.a is an installed file.  Does this work with older linkers?
> >
> >--
> >H.J.
>
> How about
>
>    /* These are all done the same way in ELF.
>       There is a new section created for each set.  */
>    #ifdef HAVE_GCC_RETAIN
>    # define attribute_used_retain_section(sec) \
>        __attribute__ ((used, retain, section (sec)))
>    #else

__attribute_used_and_retain__ is more flex and can be used
without section.

>    # define attribute_used_retain_section(sec) \
>        __attribute__ ((used, section (sec)))
>    #endif
>    #ifdef SHARED
>    /* 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_retain_section(#set) = &(symbol)
>    #else
>    # define _elf_set_element(set, symbol) \
>        static const void *const __elf_set_##set##_element_##symbol##__ \
>          attribute_used_retain_section(#set) = &(symbol)
>    #endif
> ? Yes, older linkers just ignore unknown section flags. That is the ELF spirit.
Fangrui Song March 23, 2021, 4:14 a.m. UTC | #4 
On 2021-03-22, H.J. Lu wrote:
>On Sun, Mar 21, 2021 at 9:40 PM Fangrui Song <maskray@google.com> wrote:
>>
>> On 2021-03-21, H.J. Lu wrote:
>> >On Sun, Mar 21, 2021 at 9:01 PM Fangrui Song via Libc-alpha
>> ><libc-alpha@sourceware.org> 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).
>> >> ---
>> >>  config.h.in            |  3 +++
>> >>  configure              | 23 +++++++++++++++++++++++
>> >>  configure.ac           | 16 ++++++++++++++++
>> >>  include/libc-symbols.h | 30 +++++++++++++++++++++---------
>> >>  4 files changed, 63 insertions(+), 9 deletions(-)
>> >>
>> >> diff --git a/config.h.in b/config.h.in
>> >> index f21bf04e47..cc875e90f9 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 37cef37413..28494de748 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 16b15b6f90..94ad713820 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 c83e550b03..f8eafcf1f3 100644
>> >> --- a/include/libc-symbols.h
>> >> +++ b/include/libc-symbols.h
>> >> @@ -373,17 +373,29 @@ for linking")
>> >>
>> >>  /* These are all done the same way in ELF.
>> >>     There is a new section created for each set.  */
>> >> -#ifdef SHARED
>> >> +#ifdef HAVE_GCC_RETAIN
>> >> +# ifdef SHARED
>> >>  /* 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)
>> >
>> >You should define __attribute_used_and_retain__ instead.
>> >
>> >> +  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, retain, section (#set))) = &(symbol)
>> >> +# else
>> >> +#  define _elf_set_element(set, symbol) \
>> >> +     static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> +       __attribute__ ((used, retain, section (#set))) = &(symbol)
>> >> +# endif
>> >>  #else
>> >> -# define _elf_set_element(set, symbol) \
>> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> -    __attribute__ ((used, section (#set))) = &(symbol)
>> >> -#endif
>> >> +# ifdef SHARED
>> >> +#  define _elf_set_element(set, symbol) \
>> >> +     static const void *__elf_set_##set##_element_##symbol##__ \
>> >> +       __attribute__ ((used, section (#set))) = &(symbol)
>> >> +# else
>> >> +#  define _elf_set_element(set, symbol) \
>> >> +     static const void *const __elf_set_##set##_element_##symbol##__ \
>> >> +       __attribute__ ((used, section (#set))) = &(symbol)
>> >> +# endif
>> >> +#endif /* HAVE_GCC_RETAIN  */
>> >>
>> >>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
>> >>     be able to use the set's contents.  */
>> >> --
>> >> 2.31.0.rc2.261.g7f71774620-goog
>> >>
>> >
>> >libc.a is an installed file.  Does this work with older linkers?
>> >
>> >--
>> >H.J.
>>
>> How about
>>
>>    /* These are all done the same way in ELF.
>>       There is a new section created for each set.  */
>>    #ifdef HAVE_GCC_RETAIN
>>    # define attribute_used_retain_section(sec) \
>>        __attribute__ ((used, retain, section (sec)))
>>    #else
>
>__attribute_used_and_retain__ is more flex and can be used
>without section.
>
>>    # define attribute_used_retain_section(sec) \
>>        __attribute__ ((used, section (sec)))
>>    #endif
>>    #ifdef SHARED
>>    /* 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_retain_section(#set) = &(symbol)
>>    #else
>>    # define _elf_set_element(set, symbol) \
>>        static const void *const __elf_set_##set##_element_##symbol##__ \
>>          attribute_used_retain_section(#set) = &(symbol)
>>    #endif
>> ? Yes, older linkers just ignore unknown section flags. That is the ELF spirit.
>
>
>
>-- 
>H.J.

+#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.  */
@@ -377,12 +383,12 @@ 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
H.J. Lu March 29, 2021, 11:11 p.m. UTC | #5 
On Mon, Mar 22, 2021 at 9:15 PM Fangrui Song <maskray@google.com> wrote:
>
>
> On 2021-03-22, H.J. Lu wrote:
> >On Sun, Mar 21, 2021 at 9:40 PM Fangrui Song <maskray@google.com> wrote:
> >>
> >> On 2021-03-21, H.J. Lu wrote:
> >> >On Sun, Mar 21, 2021 at 9:01 PM Fangrui Song via Libc-alpha
> >> ><libc-alpha@sourceware.org> 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).
> >> >> ---
> >> >>  config.h.in            |  3 +++
> >> >>  configure              | 23 +++++++++++++++++++++++
> >> >>  configure.ac           | 16 ++++++++++++++++
> >> >>  include/libc-symbols.h | 30 +++++++++++++++++++++---------
> >> >>  4 files changed, 63 insertions(+), 9 deletions(-)
> >> >>
> >> >> diff --git a/config.h.in b/config.h.in
> >> >> index f21bf04e47..cc875e90f9 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 37cef37413..28494de748 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 16b15b6f90..94ad713820 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 c83e550b03..f8eafcf1f3 100644
> >> >> --- a/include/libc-symbols.h
> >> >> +++ b/include/libc-symbols.h
> >> >> @@ -373,17 +373,29 @@ for linking")
> >> >>
> >> >>  /* These are all done the same way in ELF.
> >> >>     There is a new section created for each set.  */
> >> >> -#ifdef SHARED
> >> >> +#ifdef HAVE_GCC_RETAIN
> >> >> +# ifdef SHARED
> >> >>  /* 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)
> >> >
> >> >You should define __attribute_used_and_retain__ instead.
> >> >
> >> >> +  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, retain, section (#set))) = &(symbol)
> >> >> +# else
> >> >> +#  define _elf_set_element(set, symbol) \
> >> >> +     static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> +       __attribute__ ((used, retain, section (#set))) = &(symbol)
> >> >> +# endif
> >> >>  #else
> >> >> -# define _elf_set_element(set, symbol) \
> >> >> -  static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> -    __attribute__ ((used, section (#set))) = &(symbol)
> >> >> -#endif
> >> >> +# ifdef SHARED
> >> >> +#  define _elf_set_element(set, symbol) \
> >> >> +     static const void *__elf_set_##set##_element_##symbol##__ \
> >> >> +       __attribute__ ((used, section (#set))) = &(symbol)
> >> >> +# else
> >> >> +#  define _elf_set_element(set, symbol) \
> >> >> +     static const void *const __elf_set_##set##_element_##symbol##__ \
> >> >> +       __attribute__ ((used, section (#set))) = &(symbol)
> >> >> +# endif
> >> >> +#endif /* HAVE_GCC_RETAIN  */
> >> >>
> >> >>  /* Define SET as a symbol set.  This may be required (it is in a.out) to
> >> >>     be able to use the set's contents.  */
> >> >> --
> >> >> 2.31.0.rc2.261.g7f71774620-goog
> >> >>
> >> >
> >> >libc.a is an installed file.  Does this work with older linkers?
> >> >
> >> >--
> >> >H.J.
> >>
> >> How about
> >>
> >>    /* These are all done the same way in ELF.
> >>       There is a new section created for each set.  */
> >>    #ifdef HAVE_GCC_RETAIN
> >>    # define attribute_used_retain_section(sec) \
> >>        __attribute__ ((used, retain, section (sec)))
> >>    #else
> >
> >__attribute_used_and_retain__ is more flex and can be used
> >without section.
> >
> >>    # define attribute_used_retain_section(sec) \
> >>        __attribute__ ((used, section (sec)))
> >>    #endif
> >>    #ifdef SHARED
> >>    /* 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_retain_section(#set) = &(symbol)
> >>    #else
> >>    # define _elf_set_element(set, symbol) \
> >>        static const void *const __elf_set_##set##_element_##symbol##__ \
> >>          attribute_used_retain_section(#set) = &(symbol)
> >>    #endif
> >> ? Yes, older linkers just ignore unknown section flags. That is the ELF spirit.
> >
> >
> >
> >--
> >H.J.
>
> +#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.  */
> @@ -377,12 +383,12 @@ 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
>

Please submit a v2 patch.

Thanks.
diff mbox series

Patch

diff --git a/config.h.in b/config.h.in
index f21bf04e47..cc875e90f9 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 37cef37413..28494de748 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 16b15b6f90..94ad713820 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 c83e550b03..f8eafcf1f3 100644
--- a/include/libc-symbols.h
+++ b/include/libc-symbols.h
@@ -373,17 +373,29 @@  for linking")
 
 /* These are all done the same way in ELF.
    There is a new section created for each set.  */
-#ifdef SHARED
+#ifdef HAVE_GCC_RETAIN
+# ifdef SHARED
 /* 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)
+  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, retain, section (#set))) = &(symbol)
+# else
+#  define _elf_set_element(set, symbol) \
+     static const void *const __elf_set_##set##_element_##symbol##__ \
+       __attribute__ ((used, retain, section (#set))) = &(symbol)
+# endif
 #else
-# define _elf_set_element(set, symbol) \
-  static const void *const __elf_set_##set##_element_##symbol##__ \
-    __attribute__ ((used, section (#set))) = &(symbol)
-#endif
+# ifdef SHARED
+#  define _elf_set_element(set, symbol) \
+     static const void *__elf_set_##set##_element_##symbol##__ \
+       __attribute__ ((used, section (#set))) = &(symbol)
+# else
+#  define _elf_set_element(set, symbol) \
+     static const void *const __elf_set_##set##_element_##symbol##__ \
+       __attribute__ ((used, section (#set))) = &(symbol)
+# endif
+#endif /* HAVE_GCC_RETAIN  */
 
 /* Define SET as a symbol set.  This may be required (it is in a.out) to
    be able to use the set's contents.  */