From: "H.J. Lu" <hjl.tools@gmail.com>
To: Fangrui Song <maskray@google.com>
Cc: GNU C Library <libc-alpha@sourceware.org>,
Florian Weimer <fweimer@redhat.com>
Subject: Re: [PATCH v5] Set the retain attribute on _elf_set_element if CC supports [BZ #27492]
Date: Thu, 1 Apr 2021 05:52:37 -0700 [thread overview]
Message-ID: <CAMe9rOpSpNDhR0+hS6eeeSp-dRjLcxSdgzBOE-Nd8LW1gq8a1A@mail.gmail.com> (raw)
In-Reply-To: <20210401010657.3474569-1-maskray@google.com>
On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song <maskray@google.com> wrote:
>
> So that text_set_element/data_set_element/bss_set_element defined
> variables will be retained by the linker.
>
> Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
> will not be optimized out; 'retain' prevents section garbage collection
> if the linker support SHF_GNU_RETAIN.
>
> GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
> identifier name sections to be GCed even if there are live
> __start_/__stop_ references.
>
> Without the change, there are some static linking problems, e.g.
> _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
> stdout is not flushed on exit.
>
> Note: GCC may warning ‘retain’ attribute ignored while __has_attribute(retain) is 1
> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
> ---
> Changes in v1 -> v2:
> * Define attribute_used_retain_section
> Changes in v2 -> v3:
> * Use attribute_used_retain instead attribute_used_retain_section
> Changes in v3 -> v4:
> * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-cleanup* tests
> Changes in v4 -> v5:
> * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are supported
> * Rename *gcc_retain* to *gnu_retain*
> ---
> config.h.in | 3 +++
> configure | 59 ++++++++++++++++++++++++++++++++++++++++++
> configure.ac | 21 +++++++++++++++
> include/libc-symbols.h | 14 +++++++---
> libio/Makefile | 32 +++++++++++++++++++++++
> libio/tst-cleanup.c | 33 +++++++++++++++++++++++
> libio/tst-cleanup.exp | 1 +
> 7 files changed, 159 insertions(+), 4 deletions(-)
> create mode 100644 libio/tst-cleanup.c
> create mode 100644 libio/tst-cleanup.exp
>
> diff --git a/config.h.in b/config.h.in
> index ca1547ae67..96a08c7757 100644
> --- a/config.h.in
> +++ b/config.h.in
> @@ -187,6 +187,9 @@
> /* Define if gcc supports attribute ifunc. */
> #undef HAVE_GCC_IFUNC
>
> +/* Define if CC supports attribute retain. */
> +#undef HAVE_GNU_RETAIN
> +
> /* Define if the linker defines __ehdr_start. */
> #undef HAVE_EHDR_START
>
> diff --git a/configure b/configure
> index fcf43bf7de..e64b7f8efe 100755
> --- a/configure
> +++ b/configure
> @@ -4105,6 +4105,31 @@ fi
> $as_echo "$libc_cv_textrel_ifunc" >&6; }
>
>
> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
> +$as_echo_n "checking for GNU attribute retain support... " >&6; }
> +if ${libc_cv_gnu_retain+:} false; then :
> + $as_echo_n "(cached) " >&6
> +else
> + cat > conftest.c <<EOF
> +static int var __attribute__ ((used, retain, section ("__libc_atexit")));
> +EOF
> +libc_cv_gnu_retain=no
> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
> + 2>&5 ; then
> + libc_cv_gnu_retain=yes
> +fi
> +rm -f conftest*
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
> +$as_echo "$libc_cv_gnu_retain" >&6; }
> +if test $libc_cv_gnu_retain = yes; then
> + $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
> +
> +fi
> +config_vars="$config_vars
> +have-gnu-retain = $libc_cv_gnu_retain"
> +
> # Check if gcc warns about alias for function with incompatible types.
> { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
> $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
> @@ -5871,6 +5896,40 @@ fi
> $as_echo "$libc_linker_feature" >&6; }
>
>
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
> +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
> +libc_linker_feature=no
> +if test x"$gnu_ld" = x"yes"; then
> + libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
> + if test -n "$libc_linker_check"; then
> + cat > conftest.c <<EOF
> +int _start (void) { return 42; }
> +EOF
> + if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> + -Wl,-z,start-stop-gc -nostdlib -nostartfiles
> + -fPIC -shared -o conftest.so conftest.c
> + 1>&5'
> + { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> + (eval $ac_try) 2>&5
> + ac_status=$?
> + $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> + test $ac_status = 0; }; }
> + then
> + libc_linker_feature=yes
> + fi
> + rm -f conftest*
> + fi
> +fi
> +if test $libc_linker_feature = yes; then
> + libc_cv_z_start_stop_gc=yes
> +else
> + libc_cv_z_start_stop_gc=no
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> +$as_echo "$libc_linker_feature" >&6; }
> +config_vars="$config_vars
> +have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
> +
> { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
> $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
> libc_linker_feature=no
> diff --git a/configure.ac b/configure.ac
> index fce967f2c2..cc47e56e82 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -707,6 +707,23 @@ fi
> rm -f conftest*])
> AC_SUBST(libc_cv_textrel_ifunc)
>
> +# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
> +AC_CACHE_CHECK([for GNU attribute retain support],
> + libc_cv_gnu_retain, [dnl
> +cat > conftest.c <<EOF
> +static int var __attribute__ ((used, retain, section ("__libc_atexit")));
> +EOF
> +libc_cv_gnu_retain=no
> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
> + 2>&AS_MESSAGE_LOG_FD ; then
> + libc_cv_gnu_retain=yes
> +fi
> +rm -f conftest*])
> +if test $libc_cv_gnu_retain = yes; then
> + AC_DEFINE(HAVE_GNU_RETAIN)
> +fi
> +LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
> +
> # Check if gcc warns about alias for function with incompatible types.
> AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
> libc_cv_gcc_incompatible_alias, [dnl
> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
> [libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
> AC_SUBST(libc_cv_z_execstack)
>
> +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
> + [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
> +
> LIBC_LINKER_FEATURE([--no-dynamic-linker],
> [-Wl,--no-dynamic-linker],
> [libc_cv_no_dynamic_linker=yes],
> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
> index 546fc26a7b..127ea656c2 100644
> --- a/include/libc-symbols.h
> +++ b/include/libc-symbols.h
> @@ -352,6 +352,12 @@ for linking")
>
> */
>
> +#ifdef HAVE_GNU_RETAIN
> +# define attribute_used_retain __attribute__ ((__used__, __retain__))
> +#else
> +# define attribute_used_retain __attribute__ ((__used__))
> +#endif
> +
> /* Symbol set support macros. */
>
> /* Make SYMBOL, which is in the text segment, an element of SET. */
> @@ -367,12 +373,12 @@ for linking")
> /* When building a shared library, make the set section writable,
> because it will need to be relocated at run time anyway. */
> # define _elf_set_element(set, symbol) \
> - static const void *__elf_set_##set##_element_##symbol##__ \
> - __attribute__ ((used, section (#set))) = &(symbol)
> + static const void *__elf_set_##set##_element_##symbol##__ \
> + attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> #else
> # define _elf_set_element(set, symbol) \
> - static const void *const __elf_set_##set##_element_##symbol##__ \
> - __attribute__ ((used, section (#set))) = &(symbol)
> + static const void *const __elf_set_##set##_element_##symbol##__ \
> + attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
> #endif
>
> /* Define SET as a symbol set. This may be required (it is in a.out) to
> diff --git a/libio/Makefile b/libio/Makefile
> index 12ce41038f..c9c232ebc2 100644
> --- a/libio/Makefile
> +++ b/libio/Makefile
> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared))
> tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out \
> $(objpfx)tst-bz24228-mem.out
> endif
> +
> +tests += tst-cleanup-default
> +tests-static += tst-cleanup-default
> +tests-special += $(objpfx)tst-cleanup-default-cmp.out
Please make 2 tests, tst-cleanup-default and tst-cleanup-default-static.
> +LDFLAGS-tst-cleanup-default = -Wl,--gc-sections
> +
> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
> +tests += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> +tests-static += tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc
> +tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
> + $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out
Same here.
> +LDFLAGS-tst-cleanup-start-stop-gc = -Wl,--gc-sections,-z,start-stop-gc
> +LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc
> +endif
> endif
>
> include ../Rules
> @@ -224,6 +238,24 @@ $(objpfx)tst_wprintf2.out: $(gen-locales)
> $(objpfx)tst-wfile-sync.out: $(gen-locales)
> endif
>
> +$(objpfx)tst-cleanup-default-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-default.out
> + cmp $^ > $@; \
> + $(evaluate-test)
> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c
> + $(compile.c) -o $@
> +
> +$(objpfx)tst-cleanup-start-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-start-stop-gc.out
> + cmp $^ > $@; \
> + $(evaluate-test)
> +$(objpfx)tst-cleanup-start-stop-gc.o: tst-cleanup.c
> + $(compile.c) -o $@
> +
> +$(objpfx)tst-cleanup-nostart-stop-gc-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-nostart-stop-gc.out
> + cmp $^ > $@; \
> + $(evaluate-test)
> +$(objpfx)tst-cleanup-nostart-stop-gc.o: tst-cleanup.c
> + $(compile.c) -o $@
>
> $(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
> $(SHELL) $< $(common-objpfx) '$(test-program-prefix)' \
> $(common-objpfx)libio/; \
> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
> new file mode 100644
> index 0000000000..7f0a34a91e
> --- /dev/null
> +++ b/libio/tst-cleanup.c
> @@ -0,0 +1,33 @@
Please add a comment saying that test --gc-sections.
> +/* Copyright (C) 2021 Free Software Foundation, Inc.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <https://www.gnu.org/licenses/>. */
> +
> +/* Test that stdout is flushed after atexit callbacks were run. */
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +
> +void
> +hook (void)
> +{
> + puts ("hello");
> +}
> +
> +int
> +main (void)
> +{
> + atexit (hook);
> +}
> diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
> new file mode 100644
> index 0000000000..ce01362503
> --- /dev/null
> +++ b/libio/tst-cleanup.exp
> @@ -0,0 +1 @@
> +hello
> --
> 2.31.0.291.g576ba9dcdaf-goog
>
--
H.J.
next prev parent reply other threads:[~2021-04-01 12:53 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-15 1:10 [PATCH] " Fangrui Song
2021-03-15 7:28 ` Florian Weimer
2021-03-15 7:45 ` Fāng-ruì Sòng
2021-03-15 8:13 ` Florian Weimer
2021-03-22 4:00 ` [PATCH v2] " Fangrui Song
2021-03-22 4:24 ` H.J. Lu
2021-03-22 4:40 ` Fangrui Song
2021-03-22 20:28 ` H.J. Lu
2021-03-23 4:14 ` Fangrui Song
2021-03-29 23:11 ` H.J. Lu
2021-03-29 23:24 ` [PATCH v3] " Fangrui Song
2021-03-30 18:17 ` H.J. Lu
2021-03-30 19:17 ` Fāng-ruì Sòng
2021-03-30 19:30 ` H.J. Lu
2021-03-31 4:34 ` Fāng-ruì Sòng
2021-03-31 16:17 ` H.J. Lu
2021-03-31 18:09 ` Fāng-ruì Sòng
2021-03-31 18:57 ` H.J. Lu
2021-03-31 19:39 ` [PATCH v4] " Fangrui Song
2021-03-31 23:38 ` H.J. Lu
2021-04-01 0:02 ` Fangrui Song
2021-04-01 1:00 ` H.J. Lu
2021-04-01 1:06 ` [PATCH v5] " Fangrui Song
2021-04-01 12:52 ` H.J. Lu [this message]
2021-04-02 3:23 ` Fangrui Song
2021-04-02 14:14 ` H.J. Lu
2021-04-02 17:09 ` Fangrui Song
2021-04-02 17:33 ` H.J. Lu
2021-04-03 18:02 ` Fangrui Song
2021-04-03 20:47 ` H.J. Lu
2021-04-03 21:57 ` Fangrui Song
2021-04-05 1:55 ` H.J. Lu
2021-04-05 18:17 ` Fangrui Song
2021-04-05 20:35 ` H.J. Lu
2021-04-05 21:03 ` Fangrui Song
2021-04-05 21:58 ` H.J. Lu
2021-04-06 21:46 ` Fangrui Song
2021-04-09 22:36 ` Fāng-ruì Sòng
2021-04-16 3:51 ` Fāng-ruì Sòng
2021-04-16 13:00 ` H.J. Lu
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