From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-x530.google.com (mail-pg1-x530.google.com [IPv6:2607:f8b0:4864:20::530]) by sourceware.org (Postfix) with ESMTPS id AEF903858012 for ; Wed, 31 Mar 2021 04:34:17 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org AEF903858012 Received: by mail-pg1-x530.google.com with SMTP id k8so4127278pgf.4 for ; Tue, 30 Mar 2021 21:34:17 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to; bh=vga+TLYkuNTbcI+Hwvsubq9fsJtdUH0lL9WWXsFeq5c=; b=cSd7VpWWzpdKNqM/wUHaS2SBzNanvrIqKp/2rLr3FHmAMqXm01v1quwskKwB9lu54G t9h37TQqD0pJizG8VWbXQyB0yPnmRM1dwb1FcbXa+XQvR9z28odhNrHwKOmcG3oKcumy EZEzyRIPjVTBBOrJn4XU8L7CnsUuyf1imENLj4J3jVsAXNd/rRf3JvcQ/BIufXmNiaBn 81BrLVbcmaoA2Dc+TRTKhhu95mdi+ZhMmXlt3Bm7UVwZdMiDlgafPusIRUZJOOeOEDQf E64mQYxFqhENyg0wbwxzEvS7Pgm5D1OzzNEVFBRZ4qpLFu2sVSIGQa12M5HdypyYmx4s 2NOw== X-Gm-Message-State: AOAM5333dDmQq2oPwr0q+BjquDyDvZ6GS73zz/Fx4ACS9KP7u13w8EQj iWdBQUaLOeWZlKKdjNydPdEPAgCQPonImg== X-Google-Smtp-Source: ABdhPJybdIoHz9NJoSKKREFZ/cHqZEJra6gUCAOcnnd4/oKj0etvhDVWpcbIYUTjSPO/ONV5QEAgAA== X-Received: by 2002:a62:76c5:0:b029:1f2:e6af:e2ab with SMTP id r188-20020a6276c50000b02901f2e6afe2abmr1310461pfc.10.1617165256529; Tue, 30 Mar 2021 21:34:16 -0700 (PDT) Received: from google.com ([2620:15c:2ce:0:9106:8d2e:6ec7:9708]) by smtp.gmail.com with ESMTPSA id x186sm558058pfc.65.2021.03.30.21.34.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 30 Mar 2021 21:34:16 -0700 (PDT) Date: Tue, 30 Mar 2021 21:34:13 -0700 From: =?utf-8?B?RsSBbmctcnXDrCBTw7JuZw==?= To: "H.J. Lu" Cc: GNU C Library , Florian Weimer Subject: Re: [PATCH v3] Set the retain attribute on _elf_set_element if CC supports [BZ #27492] Message-ID: <20210331043413.havjfvkjw3ljhsfl@google.com> References: <20210329232440.3083493-1-maskray@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Spam-Status: No, score=-27.1 required=5.0 tests=BAYES_00, DKIMWL_WL_MED, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, ENV_AND_HDR_SPF_MATCH, GIT_PATCH_0, KAM_SHORT, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP, USER_IN_DEF_DKIM_WL, USER_IN_DEF_SPF_WL autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 31 Mar 2021 04:34:22 -0000 On 2021-03-30, H.J. Lu wrote: >On Tue, Mar 30, 2021 at 12:17 PM Fāng-ruì Sòng wrote: >> >> On Tue, Mar 30, 2021 at 11:17 AM H.J. Lu wrote: >> > >> > On Mon, Mar 29, 2021 at 4:24 PM Fangrui Song 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 <> > > +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 <> > > +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 +#include + +void +hook (void) +{ + puts ("hello"); +} + +int +main (void) +{ + atexit (hook); +}