From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oo1-xc30.google.com (mail-oo1-xc30.google.com [IPv6:2607:f8b0:4864:20::c30]) by sourceware.org (Postfix) with ESMTPS id 0351A384C003 for ; Wed, 31 Mar 2021 18:58:00 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 0351A384C003 Received: by mail-oo1-xc30.google.com with SMTP id x187-20020a4a41c40000b02901b664cf3220so4860528ooa.10 for ; Wed, 31 Mar 2021 11:57:59 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=JSlbzENq4pbwgSSo0gy3va1m5b5nhqdBNt2/btww4aQ=; b=gvHNIFe9m6PuhOwyZ4KrNFD58kYCu1nzI9AG5LT18JpksDkQv1UYLgXgopAUXYqV3s 8KeGXDniFGqQa/weVrvRDiHCSTgIxZ/vQJWmH7F5jx3cnrreBJn/aonTQkRIc4qmZRDN RsCq3b+vNcS8jcBCs5BOibhPrCtCIPMR8OebH9Sj1ogFqkq7t1R097/81A/sS/In+HEr gLW9ejExOK0TPkOD6iiXxnj9glSJe82Na6Ow/M6/TDBWiwryYERn5EAmNXcSGc0k2orD OWW+XOpYWGfA5wn59aY+0nL4F+7xFtBdRqZMHmteZ+LuOSWuNh91Gnk2nv6ZZGJ29bGx PWfw== X-Gm-Message-State: AOAM530wBnPe1rVplr+e94wjG3UTMie4arp7rYYraUTR0yJxOJaFb0wu OckIaXMSJ8e8qTMwLqJPqD4J0akD4Ok7xJ/ScEk= X-Google-Smtp-Source: ABdhPJxyUvDy6eDb1is94B0dZpGcnm79y2K28Gb+E8RAYbDfD14AuWMTRz3Hw5HNdhXKqMmLI26Mv7xlG2d/e6QwhMc= X-Received: by 2002:a4a:d1da:: with SMTP id a26mr3870025oos.58.1617217079288; Wed, 31 Mar 2021 11:57:59 -0700 (PDT) MIME-Version: 1.0 References: <20210329232440.3083493-1-maskray@google.com> <20210331043413.havjfvkjw3ljhsfl@google.com> <20210331180916.5diupvuxa6lqlg4r@google.com> In-Reply-To: <20210331180916.5diupvuxa6lqlg4r@google.com> From: "H.J. Lu" Date: Wed, 31 Mar 2021 11:57:23 -0700 Message-ID: Subject: Re: [PATCH v3] Set the retain attribute on _elf_set_element if CC supports [BZ #27492] To: =?UTF-8?B?RsSBbmctcnXDrCBTw7JuZw==?= Cc: GNU C Library , Florian Weimer Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-3035.2 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, KAM_SHORT, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP 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 18:58:03 -0000 On Wed, Mar 31, 2021 at 11:09 AM F=C4=81ng-ru=C3=AC S=C3=B2ng wrote: > > > On 2021-03-31, H.J. Lu wrote: > >On Tue, Mar 30, 2021 at 9:34 PM F=C4=81ng-ru=C3=AC S=C3=B2ng wrote: > >> > >> On 2021-03-30, H.J. Lu wrote: > >> >On Tue, Mar 30, 2021 at 12:17 PM F=C4=81ng-ru=C3=AC S=C3=B2ng wrote: > >> >> > >> >> On Tue, Mar 30, 2021 at 11:17 AM H.J. Lu wrot= e: > >> >> > > >> >> > On Mon, Mar 29, 2021 at 4:24 PM Fangrui Song = wrote: > >> >> > > > >> >> > > So that text_set_element/data_set_element/bss_set_element defin= ed > >> >> > > 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 co= llection > >> >> > > if the linker support SHF_GNU_RETAIN. > >> >> > > > >> >> > > GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allo= w 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-sectio= ns, so > >> >> > > stdout is not flushed on exit. > >> >> > > > >> >> > > Note: GCC may warning =E2=80=98retain=E2=80=99 attribute ignore= d while __has_attribute(retain) is 1 > >> >> > > (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99587). > >> >> > > --- > >> >> > > Changes in v1 -> v2: > >> >> > > * Define attribute_used_retain_section > >> >> > > Changes in v2 -> v3: > >> >> > > * Use attribute_used_retain instead attribute_used_retain_secti= on > >> >> > > --- > >> >> > > 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 attr= ibute 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=3Dno > >> >> > > +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \ > >> >> > > + 2>&5 ; then > >> >> > > + libc_cv_gcc_retain=3Dyes > >> >> > > +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 =3D yes; then > >> >> > > + $as_echo "#define HAVE_GCC_RETAIN 1" >>confdefs.h > >> >> > > + > >> >> > > +fi > >> >> > > + > >> >> > > # Check if gcc warns about alias for function with incompatibl= e 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 functio= n 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=3Dno > >> >> > > +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_L= OG_FD \ > >> >> > > + 2>&AS_MESSAGE_LOG_FD ; then > >> >> > > + libc_cv_gcc_retain=3Dyes > >> >> > > +fi > >> >> > > +rm -f conftest*]) > >> >> > > +if test $libc_cv_gcc_retain =3D yes; then > >> >> > > + AC_DEFINE(HAVE_GCC_RETAIN) > >> >> > > +fi > >> >> > > + > >> >> > > # Check if gcc warns about alias for function with incompatibl= e types. > >> >> > > AC_CACHE_CHECK([if compiler warns about alias for function wit= h 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__, __ret= ain__)) > >> >> > > +#else > >> >> > > +# define attribute_used_retain __attribute__ ((__used__)) > >> >> > > +#endif > >> >> > > + > >> >> > > /* Symbol set support macros. */ > >> >> > > > >> >> > > /* Make SYMBOL, which is in the text segment, an element of SE= T. */ > >> >> > > @@ -367,12 +373,12 @@ for linking") > >> >> > > /* When building a shared library, make the set section writab= le, > >> >> > > 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))) =3D &(symbol) > >> >> > > + static const void *__elf_set_##set##_element_##symbol##__ = \ > >> >> > > + attribute_used_retain __attribute__ ((section (#set))) = =3D &(symbol) > >> >> > > #else > >> >> > > # define _elf_set_element(set, symbol) \ > >> >> > > - static const void *const __elf_set_##set##_element_##symbol#= #__ \ > >> >> > > - __attribute__ ((used, section (#set))) =3D &(symbol) > >> >> > > + static const void *const __elf_set_##set##_element_##symbo= l##__ \ > >> >> > > + attribute_used_retain __attribute__ ((section (#set))) = =3D &(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 e= xt > >> >> 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/r= etain) > >> 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 +=3D $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenl= oc-mem.out \ > >> $(objpfx)tst-bz24228-mem.out > >> endif > >> + > >> +tests +=3D tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc > >> +tests-static +=3D tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-= gc > >> +tests-special +=3D $(objpfx)tst-cleanup-start-stop-gc.out \ > >> + $(objpfx)tst-cleanup-nostart-stop-gc.out > >> +LDFLAGS-tst-cleanup-start-stop-gc =3D -Wl,--gc-sections,-z,start-stop= -gc > >> +LDFLAGS-tst-cleanup-nostart-stop-gc =3D -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 i= t? > 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 =3D -Wl,--gc-sections,-z,nostart-sto= p-gc > +LDFLAGS-tst-cleanup-nostart-stop-gc =3D -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-st= op-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-nostar= t-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)' \ > >> $(common-objpfx)libio/; \ > >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c > >> new file mode 100644 > >> index 0000000000..de8130a482 > >> --- /dev/null > >> +++ b/libio/tst-cleanup.c > >> @@ -0,0 +1,14 @@ > > > >Missing comments and copyright notice. > > OK. I find that many tst* files don't have a copyright notice.. > Added. > > >> +#include > >> +#include > >> + > >> +void > >> +hook (void) > >> +{ > >> + puts ("hello"); > >> +} > >> + > >> +int > >> +main (void) > >> +{ > >> + atexit (hook); > >> +} > > > diff --git a/libio/Makefile b/libio/Makefile > index 12ce41038f..472a1e064c 100644 > --- a/libio/Makefile > +++ b/libio/Makefile > @@ -195,6 +195,13 @@ ifeq (yes,$(build-shared)) > tests-special +=3D $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-= mem.out \ > $(objpfx)tst-bz24228-mem.out > endif > + > +tests +=3D tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc > +tests-static +=3D tst-cleanup-start-stop-gc tst-cleanup-nostart-stop-gc > +tests-special +=3D $(objpfx)tst-cleanup-start-stop-gc-cmp.out \ > + $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out > +LDFLAGS-tst-cleanup-start-stop-gc =3D -Wl,--gc-sections,-z,start-stop-gc > +LDFLAGS-tst-cleanup-nostart-stop-gc =3D -Wl,--gc-sections,-z,nostart-sto= p-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)t= st-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 > + . */ > + > +/* Test that stdout is flushed after atexit callbacks were run. */ > + > +#include > +#include > + > +void > +hook (void) > +{ > + puts ("hello"); > +} > + > +int > +main (void) > +{ > + atexit (hook); > +} --=20 H.J.