From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi1-x22a.google.com (mail-oi1-x22a.google.com [IPv6:2607:f8b0:4864:20::22a]) by sourceware.org (Postfix) with ESMTPS id ED3193854808 for ; Fri, 2 Apr 2021 17:34:26 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org ED3193854808 Received: by mail-oi1-x22a.google.com with SMTP id i3so5553972oik.7 for ; Fri, 02 Apr 2021 10:34:26 -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=Ew4bIQIDuCNKFTqEzRaLH3moPQl57ssK3Iwx2t/Jvmg=; b=j23a44uifx+vSRAzP4DaCLgPYTa8YqEv29DFFUiF0Tm7XqPLD41TSKmrko6dlGd1EY LftS8djbKPmDjepBlJj3hZRWlkhoWlXD1aL3K4OjVvxVnRLyLdUeR/jHBKNoUh4rj9Yk HoKXFKDN1ZQiN9hRp2SxPbtHTZZlVorSJl5ZKHEwzTufMCjx5+Ypqq6wRJNLd3D6p69Z uQ16tfq8EyNoikBhi2TGuJqIKhqMnqM7RurezEl+ZPrJdid85svPsrVtdgVRnmNBDcco wDeFf3SJbeWnJdrdU0SMur8K2rpg3otxtwtdU01KaMlOy79XlK5jDBiOVKPVjbFhaKdv kCMQ== X-Gm-Message-State: AOAM531w0Dhxu2yAiPnK8d+670qfjX4rtyxIBMezvzeP07NdreW0ftui fVDC0CaqtZogHBancDOb3wXiqegdjtS1ShrhQoFOX/xp2JrguA== X-Google-Smtp-Source: ABdhPJz42r9RmyutFpCBKjnxy58jf0FCRgBqXpUq7VshUxWTwJL1dM453A5LX6/1paTPENdk90/WKWWVrpoSBcill5I= X-Received: by 2002:a05:6808:10c5:: with SMTP id s5mr10305971ois.58.1617384866159; Fri, 02 Apr 2021 10:34:26 -0700 (PDT) MIME-Version: 1.0 References: <20210401010657.3474569-1-maskray@google.com> <20210402032329.c5d3zzlrtm3d3do3@google.com> <20210402170941.evhs2o42zqq5dexq@google.com> In-Reply-To: <20210402170941.evhs2o42zqq5dexq@google.com> From: "H.J. Lu" Date: Fri, 2 Apr 2021 10:33:49 -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=-3034.7 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: Fri, 02 Apr 2021 17:34:30 -0000 On Fri, Apr 2, 2021 at 10:09 AM Fangrui Song wrote: > > On 2021-04-02, H.J. Lu wrote: > >On Thu, Apr 1, 2021 at 8:23 PM Fangrui Song wrote: > >> > >> On 2021-04-01, H.J. Lu wrote: > >> >On Wed, Mar 31, 2021 at 6:07 PM Fangrui Song wro= te: > >> >> > >> >> 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 var= iable > >> >> will not be optimized out; 'retain' prevents section garbage collec= tion > >> >> 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 wh= ile __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 ts= t-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 attribut= e 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 < >> >> +static int var __attribute__ ((used, retain, section ("__libc_ate= xit"))); > >> >> +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: $libc_cv_gnu_reta= in" >&5 > >> >> +$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 ty= pes. > >> >> { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warn= s about alias for function with incompatible types" >&5 > >> >> $as_echo_n "checking if compiler warns about alias for function wi= th 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 > >> >> +$as_echo_n "checking for linker that supports -z start-stop-gc... = " >&6; } > >> >> +libc_linker_feature=3Dno > >> >> +if test x"$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 $no_ssp > >> >> + -Wl,-z,start-stop-gc -nostdlib -nos= tartfiles > >> >> + -fPIC -shared -o conftest.so confte= st.c > >> >> + 1>&5' > >> >> + { { eval echo "\"\$as_me\":${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: $libc_linker_feat= ure" >&5 > >> >> +$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 = supports --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_ate= xit"))); > >> >> +EOF > >> >> +libc_cv_gnu_retain=3Dno > >> >> +if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_F= D \ > >> >> + 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 ty= pes. > >> >> AC_CACHE_CHECK([if compiler warns about alias for function with in= compatible types], > >> >> libc_cv_gcc_incompatible_alias, [dnl > >> >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,= execstack], > >> >> [libc_cv_z_execstack=3Dyes], [libc_cv_z_execsta= ck=3Dno]) > >> >> 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_sta= rt_stop_gc=3Dno]) > >> >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc]= ) > >> >> + > >> >> LIBC_LINKER_FEATURE([--no-dynamic-linker], > >> >> [-Wl,--no-dynamic-linker], > >> >> [libc_cv_no_dynamic_linker=3Dyes], > >> >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h > >> >> index 546fc26a7b..127ea656c2 100644 > >> >> --- a/include/libc-symbols.h > >> >> +++ b/include/libc-symbols.h > >> >> @@ -352,6 +352,12 @@ for linking") > >> >> > >> >> */ > >> >> > >> >> +#ifdef HAVE_GNU_RETAIN > >> >> +# define attribute_used_retain __attribute__ ((__used__, __retain_= _)) > >> >> +#else > >> >> +# define attribute_used_retain __attribute__ ((__used__)) > >> >> +#endif > >> >> + > >> >> /* Symbol set support macros. */ > >> >> > >> >> /* Make SYMBOL, which is in the text segment, an element of SET. = */ > >> >> @@ -367,12 +373,12 @@ for linking") > >> >> /* When building a shared library, make the set section writable, > >> >> because it will need to be relocated at run time anyway. */ > >> >> # define _elf_set_element(set, symbol) \ > >> >> - static const void *__elf_set_##set##_element_##symbol##__ \ > >> >> - __attribute__ ((used, section (#set))) =3D &(symbol) > >> >> + static const void *__elf_set_##set##_element_##symbol##__ \ > >> >> + attribute_used_retain __attribute__ ((section (#set))) =3D &= (symbol) > >> >> #else > >> >> # define _elf_set_element(set, symbol) \ > >> >> - static const void *const __elf_set_##set##_element_##symbol##__ = \ > >> >> - __attribute__ ((used, section (#set))) =3D &(symbol) > >> >> + static const void *const __elf_set_##set##_element_##symbol##_= _ \ > >> >> + attribute_used_retain __attribute__ ((section (#set))) =3D &= (symbol) > >> >> #endif > >> >> > >> >> /* Define SET as a symbol set. This may be required (it is in a.o= ut) to > >> >> diff --git a/libio/Makefile b/libio/Makefile > >> >> index 12ce41038f..c9c232ebc2 100644 > >> >> --- a/libio/Makefile > >> >> +++ b/libio/Makefile > >> >> @@ -195,6 +195,20 @@ ifeq (yes,$(build-shared)) > >> >> tests-special +=3D $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fope= nloc-mem.out \ > >> >> $(objpfx)tst-bz24228-mem.out > >> >> endif > >> >> + > >> >> +tests +=3D tst-cleanup-default > >> >> +tests-static +=3D tst-cleanup-default > >> >> +tests-special +=3D $(objpfx)tst-cleanup-default-cmp.out > >> > > >> >Please make 2 tests, tst-cleanup-default and tst-cleanup-default-sta= tic. > >> > >> Added. > >> > >> >> +LDFLAGS-tst-cleanup-default =3D -Wl,--gc-sections > >> >> + > >> >> +ifeq ($(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-st= op-gc > >> >> +tests-special +=3D $(objpfx)tst-cleanup-start-stop-gc-cmp.out \ > >> >> + $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out > >> > > >> >Same here. > >> > >> Added. > >> > >> >> +LDFLAGS-tst-cleanup-start-stop-gc =3D -Wl,--gc-sections,-z,start-s= top-gc > >> >> +LDFLAGS-tst-cleanup-nostart-stop-gc =3D -Wl,--gc-sections,-z,nosta= rt-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 $(objp= fx)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 $(ob= jpfx)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. > >> > >> OK, added. > >> > >> >> +/* 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 versi= on. > >> >> + > >> >> + The GNU C Library is distributed in the hope that it will be us= eful, > >> >> + but WITHOUT ANY WARRANTY; without even the implied warranty of > >> >> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the G= NU > >> >> + Lesser General Public License for more details. > >> >> + > >> >> + You should have received a copy of the GNU Lesser General Publi= c > >> >> + 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 > >> >> > >> > > >> > >> 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_us= ed_retain macro. > >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute r= etain 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 type= s. > >> { $as_echo "$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 sup= ports -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`$LD -v --help 2>/dev/null | grep "\-z start-st= op-gc"` > >> + if test -n "$libc_linker_check"; then > >> + cat > conftest.c < >> +int _start (void) { return 42; } > >> +EOF > >> + if { ac_try=3D'${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp > >> + -Wl,-z,start-stop-gc -nostdlib -nostar= tfiles > >> + -fPIC -shared -o conftest.so conftest.= c > >> + 1>&5' > >> + { { eval echo "\"\$as_me\":${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 su= pports --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_us= ed_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 type= s. > >> AC_CACHE_CHECK([if compiler warns about alias for function with inco= mpatible types], > >> libc_cv_gcc_incompatible_alias, [dnl > >> @@ -1317,6 +1334,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,exe= cstack], > >> [libc_cv_z_execstack=3Dyes], [libc_cv_z_execstack= =3Dno]) > >> 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_= stop_gc=3Dno]) > >> +LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc]) > >> + > >> LIBC_LINKER_FEATURE([--no-dynamic-linker], > >> [-Wl,--no-dynamic-linker], > >> [libc_cv_no_dynamic_linker=3Dyes], > >> diff --git a/include/libc-symbols.h b/include/libc-symbols.h > >> index 546fc26a7b..127ea656c2 100644 > >> --- a/include/libc-symbols.h > >> +++ b/include/libc-symbols.h > >> @@ -352,6 +352,12 @@ for linking") > >> > >> */ > >> > >> +#ifdef HAVE_GNU_RETAIN > >> +# define attribute_used_retain __attribute__ ((__used__, __retain__)) > >> +#else > >> +# define attribute_used_retain __attribute__ ((__used__)) > >> +#endif > >> + > >> /* Symbol set support macros. */ > >> > >> /* Make SYMBOL, which is in the text segment, an element of SET. */ > >> @@ -367,12 +373,12 @@ for linking") > >> /* When building a shared library, make the set section writable, > >> because it will need to be relocated at run time anyway. */ > >> # define _elf_set_element(set, symbol) \ > >> - static const void *__elf_set_##set##_element_##symbol##__ \ > >> - __attribute__ ((used, section (#set))) =3D &(symbol) > >> + static const void *__elf_set_##set##_element_##symbol##__ \ > >> + attribute_used_retain __attribute__ ((section (#set))) =3D &(sy= mbol) > >> #else > >> # define _elf_set_element(set, symbol) \ > >> - static const void *const __elf_set_##set##_element_##symbol##__ \ > >> - __attribute__ ((used, section (#set))) =3D &(symbol) > >> + static const void *const __elf_set_##set##_element_##symbol##__ \ > >> + attribute_used_retain __attribute__ ((section (#set))) =3D &(sy= mbol) > >> #endif > >> > >> /* Define SET as a symbol set. This may be required (it is in a.out= ) to > >> diff --git a/libio/Makefile b/libio/Makefile > >> index 12ce41038f..ad0d53bb49 100644 > >> --- a/libio/Makefile > >> +++ b/libio/Makefile > >> @@ -195,6 +195,26 @@ ifeq (yes,$(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-default tst-cleanup-default-static > >> +tests-static +=3D tst-cleanup-default-static > >> +tests-special +=3D $(objpfx)tst-cleanup-default-cmp.out $(objpfx)tst-= cleanup-default-static-cmp.out > >> +LDFLAGS-tst-cleanup-default =3D -Wl,--gc-sections > >> +LDFLAGS-tst-cleanup-default-static =3D -Wl,--gc-sections > >> + > >> +ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes) > >> +tests +=3D tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static= \ > >> + tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-g= c-static > >> +tests-static +=3D tst-cleanup-start-stop-gc-static tst-cleanup-nostar= t-stop-gc-static > >> +tests-special +=3D $(objpfx)tst-cleanup-start-stop-gc-cmp.out \ > >> + $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \ > >> + $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \ > >> + $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out > >> +LDFLAGS-tst-cleanup-start-stop-gc :=3D -Wl,--gc-sections,-z,start-sto= p-gc > >> +LDFLAGS-tst-cleanup-start-stop-gc-static :=3D -Wl,--gc-sections,-z,st= art-stop-gc > >> +LDFLAGS-tst-cleanup-nostart-stop-gc :=3D -Wl,--gc-sections,-z,nostart= -stop-gc > >> +LDFLAGS-tst-cleanup-nostart-stop-gc-static :=3D -Wl,--gc-sections,-z,= nostart-stop-gc > >> +endif > >> endif > >> > >> include ../Rules > >> @@ -224,6 +244,39 @@ $(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-cl= eanup-default.out > >> + cmp $^ > $@; \ > >> + $(evaluate-test) > >> +$(objpfx)tst-cleanup-default.o: tst-cleanup.c > >> + $(compile.c) -o $@ > >> +$(objpfx)tst-cleanup-default-static-cmp.out: tst-cleanup.exp $(objpfx= )tst-cleanup-default-static.out > >> + cmp $^ > $@; \ > >> + $(evaluate-test) > >> +$(objpfx)tst-cleanup-default-static.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-start-stop-gc-static-cmp.out: tst-cleanup.exp $(= objpfx)tst-cleanup-start-stop-gc-static.out > >> + cmp $^ > $@; \ > >> + $(evaluate-test) > >> +$(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c > >> + $(compile.c) -o $@ > > > >Please add a separate .c file for each test to get the correct dependenc= y. > > This is unnecessary. > > $(objpfx)tst-cleanup-start-stop-gc-static.o: tst-cleanup.c > > does the work perfectly. > What does tst-cleanup-start-stop-gc-static.o.d contain? --=20 H.J.