From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot1-x32f.google.com (mail-ot1-x32f.google.com [IPv6:2607:f8b0:4864:20::32f]) by sourceware.org (Postfix) with ESMTPS id 9BA113858012 for ; Thu, 1 Apr 2021 12:53:14 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 9BA113858012 Received: by mail-ot1-x32f.google.com with SMTP id m21-20020a9d7ad50000b02901b83efc84a0so1973543otn.10 for ; Thu, 01 Apr 2021 05:53:14 -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=HQvsGjDTkfuGj87wx+t0Hktav+khUFOU3SExKRsh7TU=; b=TmzWQ/XnpDYpL+r5xINDG7rNBWhwVT6HpX2+19tkXBSzPfIK+x8QIZTbgPsuyLDOrH soDiku50Hlo/CkLpsQqitkpU4Az6E/S5ASoAVsb4JkvXqxHRQp2huqTOaTdFNvFxdPDt XSp+aDl0bC3bCgN3/iSTb2HCL6B1R3V9NPFc3+Yf9jo6ZiX/gtUJLRfHH8K7cP/c3jeu X7ocEy/1M8xQhvNX7p8ebr4HbBJPMGVxW0bDRo9VLKyrJ+dnpTRDo80f1MAXKsXKqeoD lovOtChTMb1tUAjZn7ov6JRgm5eF0H61S4nJ5LVudWeYARqSYjf+MuQjdLWPOodzwTct GsCQ== X-Gm-Message-State: AOAM532+9arA2TBKloVrkSb6uHVwE8lRS9BO6/TUaL1RHhajiDsNuusd DP72tb4D9BSa7h8QVIiEci0ZzcuPC31VY7n2EFkbrYeFlVAk1g== X-Google-Smtp-Source: ABdhPJz30ty2amyLpSJCTYiZptFn1WLbEf8fGnCOY46Gf06r42/3n6Nyc+3LZq09afGaAZ11x0vjpQgrFzPrtqrA/Eg= X-Received: by 2002:a05:6830:1515:: with SMTP id k21mr6688074otp.269.1617281593964; Thu, 01 Apr 2021 05:53:13 -0700 (PDT) MIME-Version: 1.0 References: <20210401010657.3474569-1-maskray@google.com> In-Reply-To: <20210401010657.3474569-1-maskray@google.com> From: "H.J. Lu" Date: Thu, 1 Apr 2021 05:52:37 -0700 Message-ID: Subject: Re: [PATCH v5] Set the retain attribute on _elf_set_element if CC supports [BZ #27492] To: Fangrui Song Cc: GNU C Library , Florian Weimer Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-3036.6 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: Thu, 01 Apr 2021 12:53:19 -0000 On Wed, Mar 31, 2021 at 6:07 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 =E2=80=98retain=E2=80=99 attribute ignored 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_section > Changes in v3 -> v4: > * Add LIBC_LINKER_FEATURE detection for -z start-stop-gc and add tst-clea= nup* tests > Changes in v4 -> v5: > * Enable -z start-stop-gc tests if both retain and -z start-stop-gc are s= upported > * 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 reta= in 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 < +static int var __attribute__ ((used, retain, section ("__libc_atexit"))= ); > +EOF > +libc_cv_gnu_retain=3Dno > +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \ > + 2>&5 ; then > + libc_cv_gnu_retain=3Dyes > +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 =3D yes; then > + $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h > + > +fi > +config_vars=3D"$config_vars > +have-gnu-retain =3D $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 abou= t alias for function with incompatible types" >&5 > $as_echo_n "checking if compiler warns about alias for function with inc= ompatible types... " >&6; } > @@ -5871,6 +5896,40 @@ fi > $as_echo "$libc_linker_feature" >&6; } > > > +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that suppor= ts -z start-stop-gc" >&5 > +$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6;= } > +libc_linker_feature=3Dno > +if test x"$gnu_ld" =3D x"yes"; then > + libc_linker_check=3D`$LD -v --help 2>/dev/null | grep "\-z start-stop-= gc"` > + if test -n "$libc_linker_check"; then > + cat > conftest.c < +int _start (void) { return 42; } > +EOF > + if { ac_try=3D'${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp > + -Wl,-z,start-stop-gc -nostdlib -nostartfi= les > + -fPIC -shared -o conftest.so conftest.c > + 1>&5' > + { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5 > + (eval $ac_try) 2>&5 > + ac_status=3D$? > + $as_echo "$as_me:${as_lineno-$LINENO}: \$? =3D $ac_status" >&5 > + test $ac_status =3D 0; }; } > + then > + libc_linker_feature=3Dyes > + fi > + rm -f conftest* > + fi > +fi > +if test $libc_linker_feature =3D yes; then > + libc_cv_z_start_stop_gc=3Dyes > +else > + libc_cv_z_start_stop_gc=3Dno > +fi > +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >= &5 > +$as_echo "$libc_linker_feature" >&6; } > +config_vars=3D"$config_vars > +have-z-start-stop-gc =3D $libc_cv_z_start_stop_gc" > + > { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that suppor= ts --no-dynamic-linker" >&5 > $as_echo_n "checking for linker that supports --no-dynamic-linker... " >= &6; } > libc_linker_feature=3Dno > 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 < +static int var __attribute__ ((used, retain, section ("__libc_atexit"))= ); > +EOF > +libc_cv_gnu_retain=3Dno > +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=3Dyes > +fi > +rm -f conftest*]) > +if test $libc_cv_gnu_retain =3D yes; then > + AC_DEFINE(HAVE_GNU_RETAIN) > +fi > +LIBC_CONFIG_VAR([have-gnu-retain], [$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 incompat= ible types], > libc_cv_gcc_incompatible_alias, [dnl > @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execst= ack], > [libc_cv_z_execstack=3Dyes], [libc_cv_z_execstack=3Dn= o]) > AC_SUBST(libc_cv_z_execstack) > > +LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc], > + [libc_cv_z_start_stop_gc=3Dyes], [libc_cv_z_start_sto= p_gc=3Dno]) > +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc]) > + > LIBC_LINKER_FEATURE([--no-dynamic-linker], > [-Wl,--no-dynamic-linker], > [libc_cv_no_dynamic_linker=3Dyes], > diff --git a/include/libc-symbols.h b/include/libc-symbols.h > index 546fc26a7b..127ea656c2 100644 > --- a/include/libc-symbols.h > +++ b/include/libc-symbols.h > @@ -352,6 +352,12 @@ for linking") > > */ > > +#ifdef HAVE_GNU_RETAIN > +# define attribute_used_retain __attribute__ ((__used__, __retain__)) > +#else > +# define attribute_used_retain __attribute__ ((__used__)) > +#endif > + > /* Symbol set support macros. */ > > /* Make SYMBOL, which is in the text segment, an element of SET. */ > @@ -367,12 +373,12 @@ for linking") > /* When building a shared library, make the set section writable, > because it will need to be relocated at run time anyway. */ > # define _elf_set_element(set, symbol) \ > - static const void *__elf_set_##set##_element_##symbol##__ \ > - __attribute__ ((used, section (#set))) =3D &(symbol) > + static const void *__elf_set_##set##_element_##symbol##__ \ > + attribute_used_retain __attribute__ ((section (#set))) =3D &(symbo= l) > #else > # define _elf_set_element(set, symbol) \ > - static const void *const __elf_set_##set##_element_##symbol##__ \ > - __attribute__ ((used, section (#set))) =3D &(symbol) > + static const void *const __elf_set_##set##_element_##symbol##__ \ > + attribute_used_retain __attribute__ ((section (#set))) =3D &(symbo= l) > #endif > > /* Define SET as a symbol set. This may be required (it is in a.out) to > diff --git a/libio/Makefile b/libio/Makefile > index 12ce41038f..c9c232ebc2 100644 > --- a/libio/Makefile > +++ b/libio/Makefile > @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared)) > tests-special +=3D $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-m= em.out \ > $(objpfx)tst-bz24228-mem.out > endif > + > +tests +=3D tst-cleanup-default > +tests-static +=3D tst-cleanup-default > +tests-special +=3D $(objpfx)tst-cleanup-default-cmp.out Please make 2 tests, tst-cleanup-default and tst-cleanup-default-static. > +LDFLAGS-tst-cleanup-default =3D -Wl,--gc-sections > + > +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes) > +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 Same here. > +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 > 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-clean= up-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)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 @@ 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 > + . */ > + > +/* Test that stdout is flushed after atexit callbacks were run. */ > + > +#include > +#include > + > +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 > --=20 H.J.