From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-x52e.google.com (mail-pg1-x52e.google.com [IPv6:2607:f8b0:4864:20::52e]) by sourceware.org (Postfix) with ESMTPS id 7112738515F1 for ; Wed, 31 Mar 2021 18:09:21 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 7112738515F1 Received: by mail-pg1-x52e.google.com with SMTP id f3so5536098pgv.0 for ; Wed, 31 Mar 2021 11:09:21 -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=Zi+g6x/BDwHxbLYMsIB+buxIBHUFMBecfuPiWpEmq0E=; b=O1b4u2lxQrjg03bG7jnzbPMOli7EhwjON3bjzogwOUhhMa6v/YZEcyi2fEL3OBDXHx VrLILUs3v/UKfQF+tUx7yc0B5GNzIwZuhYO7iIHYcd3jgAPmjYGnVyOua1EvGp4EF0Hv fNpYpe85WOu57rBPYylDm0lWmoDJFjIEUc6DCuhIcaHOu4OzPkJZRH6sLD1dQl+ovne5 e7sPZOCyhR3JCanNqxuzRx/L5jlgHdCGjo7ktjSHdU+4Hs3x39j3qKx48BdG03zogUud 8lPHWKq8ayC/DnDZtdY6tZ5GvtllnmW2yf5tpqneRarqTHHkZxHzaM+dPyeafscZlkXk Q12Q== X-Gm-Message-State: AOAM533lzgDHVMmaGy0vRneJUs8kN9k9x/hzh3PQNbl4sALNWQi2osmC dflAmrxs/a0vOUigp9b8L4Xxyym4nn6sgw== X-Google-Smtp-Source: ABdhPJyuYUs3xlKA12YWaC5GLriRmATMK9xziGMwdYkfTqY2NC08tAVjJBy9vrXiFNESgbtzcFmt5Q== X-Received: by 2002:a62:2d6:0:b029:204:9b3b:dced with SMTP id 205-20020a6202d60000b02902049b3bdcedmr4130198pfc.36.1617214160366; Wed, 31 Mar 2021 11:09:20 -0700 (PDT) Received: from google.com ([2620:15c:2ce:0:9106:8d2e:6ec7:9708]) by smtp.gmail.com with ESMTPSA id b19sm2891165pfo.7.2021.03.31.11.09.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 31 Mar 2021 11:09:19 -0700 (PDT) Date: Wed, 31 Mar 2021 11:09:16 -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: <20210331180916.5diupvuxa6lqlg4r@google.com> References: <20210329232440.3083493-1-maskray@google.com> <20210331043413.havjfvkjw3ljhsfl@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=-27.2 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 18:09:25 -0000 On 2021-03-31, H.J. Lu wrote: >On Tue, Mar 30, 2021 at 9:34 PM Fāng-ruì Sòng wrote: >> >> 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 > >1. Need to check if linker supports -z start-stop-gc. This seems difficult to do with Makefile... Second, do we need to check it? ld warns instead of errors for an unknown -z option, so not checking it may be fine. (GNU ld warns even with --fatal-warnings.) >2. Need to test with only -Wl,--gc-sections. OK, removed -z,nostart-stop-gc -LDFLAGS-tst-cleanup-nostart-stop-gc = -Wl,--gc-sections,-z,nostart-stop-gc +LDFLAGS-tst-cleanup-nostart-stop-gc = -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-stop-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-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)' \ >> $(common-objpfx)libio/; \ >> diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c >> new file mode 100644 >> index 0000000000..de8130a482 >> --- /dev/null >> +++ b/libio/tst-cleanup.c >> @@ -0,0 +1,14 @@ > >Missing comments and copyright notice. OK. I find that many tst* files don't have a copyright notice.. Added. >> +#include >> +#include >> + >> +void >> +hook (void) >> +{ >> + puts ("hello"); >> +} >> + >> +int >> +main (void) >> +{ >> + atexit (hook); >> +} diff --git a/libio/Makefile b/libio/Makefile index 12ce41038f..472a1e064c 100644 --- a/libio/Makefile +++ b/libio/Makefile @@ -195,6 +195,13 @@ ifeq (yes,$(build-shared)) tests-special += $(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-cmp.out \ + $(objpfx)tst-cleanup-nostart-stop-gc-cmp.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 +231,18 @@ $(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)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 @@ +/* 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); +}