From patchwork Wed May 20 18:12:27 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Florian Weimer X-Patchwork-Id: 39344 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 3BC02395A837; Wed, 20 May 2020 18:12:46 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 3BC02395A837 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1589998366; bh=zBE7ruwI9hK2iyPDM2u9YJpM5C4Ei0D+c9mPnXgK7Kc=; h=To:Subject:In-Reply-To:References:Date:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To: From; b=lT4CWgtGiXqV1sXrF5e+SRj/Y7AraDn8nDLbEiCHieCZWTiLQjrdgKuSso9Y2cJUt bBXOdCsZC9jOPiXx8o6TL8leNjZI34sSWuKsLJEbc/cilLsVMcd/Bfw2auhIVlvBh2 i7QhaaCtK/+6eZdcb5np/0V2Z3Myr+sLlBSTzNWg= X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from us-smtp-delivery-1.mimecast.com (us-smtp-1.mimecast.com [207.211.31.81]) by sourceware.org (Postfix) with ESMTP id A58EF385DC32 for ; Wed, 20 May 2020 18:12:39 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org A58EF385DC32 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-419-eQb3jVoDOHesRgRuwLwVhQ-1; Wed, 20 May 2020 14:12:30 -0400 X-MC-Unique: eQb3jVoDOHesRgRuwLwVhQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EEB0D80183C for ; Wed, 20 May 2020 18:12:29 +0000 (UTC) Received: from oldenburg2.str.redhat.com (ovpn-113-191.ams2.redhat.com [10.36.113.191]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C2B744734E for ; Wed, 20 May 2020 18:12:28 +0000 (UTC) To: libc-alpha@sourceware.org Subject: [PATCH 1/2] Add the __libc_single_threaded variable In-Reply-To: References: Message-Id: Date: Wed, 20 May 2020 20:12:27 +0200 User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-Spam-Status: No, score=-14.0 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_SHORT, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, 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-Patchwork-Original-From: Florian Weimer via Libc-alpha From: Florian Weimer Reply-To: Florian Weimer Errors-To: libc-alpha-bounces@sourceware.org Sender: "Libc-alpha" The variable is placed in libc.so, and it can be true only in an outer libc, not libcs loaded via dlmopen or static dlopen. Since thread creation from inner namespaces does not work, pthread_create can update __libc_single_threaded directly. Using __libc_early_init and its initial flag, implementation of this variable is very straightforward. A future version may reset the flag during fork (but not in an inner namespace), or after joining all threads except one. --- NEWS | 6 + elf/Makefile | 33 +++- elf/libc_early_init.c | 4 + elf/tst-single_threaded-mod1.c | 25 +++ elf/tst-single_threaded-mod2.c | 25 +++ elf/tst-single_threaded-mod3.c | 25 +++ elf/tst-single_threaded-mod4.c | 25 +++ elf/tst-single_threaded-pthread-static.c | 86 +++++++++ elf/tst-single_threaded-pthread.c | 174 ++++++++++++++++++ elf/tst-single_threaded-static-dlopen.c | 56 ++++++ elf/tst-single_threaded-static.c | 29 +++ elf/tst-single_threaded.c | 70 +++++++ htl/pt-create.c | 5 + include/sys/single_threaded.h | 1 + misc/Makefile | 5 +- misc/Versions | 3 + misc/single_threaded.c | 27 +++ misc/sys/single_threaded.h | 33 ++++ nptl/pthread_create.c | 5 + sysdeps/generic/ldsodefs.h | 5 + sysdeps/generic/libc.abilist | 1 + sysdeps/mach/hurd/i386/libc.abilist | 1 + sysdeps/unix/sysv/linux/aarch64/libc.abilist | 1 + sysdeps/unix/sysv/linux/alpha/libc.abilist | 1 + sysdeps/unix/sysv/linux/arm/be/libc.abilist | 1 + sysdeps/unix/sysv/linux/arm/le/libc.abilist | 1 + sysdeps/unix/sysv/linux/csky/libc.abilist | 1 + sysdeps/unix/sysv/linux/hppa/libc.abilist | 1 + sysdeps/unix/sysv/linux/i386/libc.abilist | 1 + sysdeps/unix/sysv/linux/ia64/libc.abilist | 1 + .../sysv/linux/m68k/coldfire/libc.abilist | 1 + .../unix/sysv/linux/m68k/m680x0/libc.abilist | 1 + .../sysv/linux/microblaze/be/libc.abilist | 1 + .../sysv/linux/microblaze/le/libc.abilist | 1 + .../sysv/linux/mips/mips32/fpu/libc.abilist | 1 + .../sysv/linux/mips/mips32/nofpu/libc.abilist | 1 + .../sysv/linux/mips/mips64/n32/libc.abilist | 1 + .../sysv/linux/mips/mips64/n64/libc.abilist | 1 + sysdeps/unix/sysv/linux/nios2/libc.abilist | 1 + .../linux/powerpc/powerpc32/fpu/libc.abilist | 1 + .../powerpc/powerpc32/nofpu/libc.abilist | 1 + .../linux/powerpc/powerpc64/be/libc.abilist | 1 + .../linux/powerpc/powerpc64/le/libc.abilist | 1 + .../unix/sysv/linux/riscv/rv64/libc.abilist | 1 + .../unix/sysv/linux/s390/s390-32/libc.abilist | 1 + .../unix/sysv/linux/s390/s390-64/libc.abilist | 1 + sysdeps/unix/sysv/linux/sh/be/libc.abilist | 1 + sysdeps/unix/sysv/linux/sh/le/libc.abilist | 1 + .../sysv/linux/sparc/sparc32/libc.abilist | 1 + .../sysv/linux/sparc/sparc64/libc.abilist | 1 + .../unix/sysv/linux/x86_64/64/libc.abilist | 1 + .../unix/sysv/linux/x86_64/x32/libc.abilist | 1 + 52 files changed, 666 insertions(+), 8 deletions(-) create mode 100644 elf/tst-single_threaded-mod1.c create mode 100644 elf/tst-single_threaded-mod2.c create mode 100644 elf/tst-single_threaded-mod3.c create mode 100644 elf/tst-single_threaded-mod4.c create mode 100644 elf/tst-single_threaded-pthread-static.c create mode 100644 elf/tst-single_threaded-pthread.c create mode 100644 elf/tst-single_threaded-static-dlopen.c create mode 100644 elf/tst-single_threaded-static.c create mode 100644 elf/tst-single_threaded.c create mode 100644 include/sys/single_threaded.h create mode 100644 misc/single_threaded.c create mode 100644 misc/sys/single_threaded.h diff --git a/NEWS b/NEWS index b7c229b32a..0230f0a58e 100644 --- a/NEWS +++ b/NEWS @@ -27,6 +27,12 @@ Major new features: several APIs have been annotated with GCC 'access' attribute. This should help GCC 10 issue better warnings. +* The GNU C Library now provides the header file + which declares the variable __libc_single_threaded. Applications are + encouraged to use this variable for single-thread optimizations, + instead of weak references to symbols historically defined in + libpthread. + Deprecated and removed features, and other changes affecting compatibility: * The deprecated header and the sysctl function have been diff --git a/elf/Makefile b/elf/Makefile index 6fe1df90bb..81a696c3ef 100644 --- a/elf/Makefile +++ b/elf/Makefile @@ -155,7 +155,9 @@ endif tests-static-normal := tst-leaks1-static tst-array1-static tst-array5-static \ tst-dl-iter-static \ tst-tlsalign-static tst-tlsalign-extern-static \ - tst-linkall-static tst-env-setuid tst-env-setuid-tunables + tst-linkall-static tst-env-setuid tst-env-setuid-tunables \ + tst-single_threaded-static tst-single_threaded-pthread-static + tests-static-internal := tst-tls1-static tst-tls2-static \ tst-ptrguard1-static tst-stackguard1-static \ tst-tls1-static-non-pie tst-libc_dlvsym-static @@ -174,9 +176,11 @@ tests-internal := tst-tls1 tst-tls2 $(tests-static-internal) tests-static := $(tests-static-normal) $(tests-static-internal) ifeq (yes,$(build-shared)) -tests-static += tst-tls9-static -tst-tls9-static-ENV = \ - LD_LIBRARY_PATH=$(objpfx):$(common-objpfx):$(common-objpfx)dlfcn +tests-static += tst-tls9-static tst-single_threaded-static-dlopen +static-dlopen-environment = \ + LD_LIBRARY_PATH=$(objpfx):$(common-objpfx):$(common-objpfx)dlfcn +tst-tls9-static-ENV = $(static-dlopen-environment) +tst-single_threaded-static-dlopen-ENV = $(static-dlopen-environment) tests += restest1 preloadtest loadfail multiload origtest resolvfail \ constload1 order noload filter \ @@ -204,7 +208,8 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \ tst-dlopen-self tst-auditmany tst-initfinilazyfail tst-dlopenfail \ tst-dlopenfail-2 \ tst-filterobj tst-filterobj-dlopen tst-auxobj tst-auxobj-dlopen \ - tst-audit14 tst-audit15 tst-audit16 + tst-audit14 tst-audit15 tst-audit16 \ + tst-single_threaded tst-single_threaded-pthread # reldep9 tests-internal += loadtest unload unload2 circleload1 \ neededtest neededtest2 neededtest3 neededtest4 \ @@ -317,7 +322,9 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \ tst-dlopenfailmod1 tst-dlopenfaillinkmod tst-dlopenfailmod2 \ tst-dlopenfailmod3 tst-ldconfig-ld-mod \ tst-filterobj-flt tst-filterobj-aux tst-filterobj-filtee \ - tst-auditlogmod-1 tst-auditlogmod-2 tst-auditlogmod-3 + tst-auditlogmod-1 tst-auditlogmod-2 tst-auditlogmod-3 \ + tst-single_threaded-mod1 tst-single_threaded-mod2 \ + tst-single_threaded-mod3 tst-single_threaded-mod4 # Most modules build with _ISOMAC defined, but those filtered out # depend on internal headers. modules-names-tests = $(filter-out ifuncmod% tst-libc_dlvsym-dso tst-tlsmod%,\ @@ -1748,3 +1755,17 @@ $(objpfx)tst-auxobj: $(objpfx)tst-filterobj-aux.so $(objpfx)tst-auxobj-dlopen: $(libdl) $(objpfx)tst-auxobj.out: $(objpfx)tst-filterobj-filtee.so $(objpfx)tst-auxobj-dlopen.out: $(objpfx)tst-filterobj-filtee.so + +$(objpfx)tst-single_threaded: $(objpfx)tst-single_threaded-mod1.so $(libdl) +$(objpfx)tst-single_threaded.out: \ + $(objpfx)tst-single_threaded-mod2.so $(objpfx)tst-single_threaded-mod3.so +$(objpfx)tst-single_threaded-static-dlopen: \ + $(objpfx)tst-single_threaded-mod1.o $(common-objpfx)dlfcn/libdl.a +$(objpfx)tst-single_threaded-static-dlopen.out: \ + $(objpfx)tst-single_threaded-mod2.so +$(objpfx)tst-single_threaded-pthread: \ + $(objpfx)tst-single_threaded-mod1.so $(libdl) $(shared-thread-library) +$(objpfx)tst-single_threaded-pthread.out: \ + $(objpfx)tst-single_threaded-mod2.so $(objpfx)tst-single_threaded-mod3.so \ + $(objpfx)tst-single_threaded-mod4.so +$(objpfx)tst-single_threaded-pthread-static: $(static-thread-library) diff --git a/elf/libc_early_init.c b/elf/libc_early_init.c index e6c64fb526..725ab2f811 100644 --- a/elf/libc_early_init.c +++ b/elf/libc_early_init.c @@ -18,10 +18,14 @@ #include #include +#include void __libc_early_init (_Bool initial) { /* Initialize ctype data. */ __ctype_init (); + + /* Only the outer namespace is marked as single-threaded. */ + __libc_single_threaded = initial; } diff --git a/elf/tst-single_threaded-mod1.c b/elf/tst-single_threaded-mod1.c new file mode 100644 index 0000000000..9fe94b2526 --- /dev/null +++ b/elf/tst-single_threaded-mod1.c @@ -0,0 +1,25 @@ +/* Test support for single-thread optimizations. Shared object 1. + Copyright (C) 2019 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 + . */ + +#include + +_Bool +single_threaded_1 (void) +{ + return __libc_single_threaded; +} diff --git a/elf/tst-single_threaded-mod2.c b/elf/tst-single_threaded-mod2.c new file mode 100644 index 0000000000..a5166c9ebc --- /dev/null +++ b/elf/tst-single_threaded-mod2.c @@ -0,0 +1,25 @@ +/* Test support for single-thread optimizations. Shared object 2. + Copyright (C) 2019 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 + . */ + +#include + +_Bool +single_threaded_2 (void) +{ + return __libc_single_threaded; +} diff --git a/elf/tst-single_threaded-mod3.c b/elf/tst-single_threaded-mod3.c new file mode 100644 index 0000000000..53df13e3a7 --- /dev/null +++ b/elf/tst-single_threaded-mod3.c @@ -0,0 +1,25 @@ +/* Test support for single-thread optimizations. Shared object 3. + Copyright (C) 2019 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 + . */ + +#include + +_Bool +single_threaded_3 (void) +{ + return __libc_single_threaded; +} diff --git a/elf/tst-single_threaded-mod4.c b/elf/tst-single_threaded-mod4.c new file mode 100644 index 0000000000..3bf5e555a4 --- /dev/null +++ b/elf/tst-single_threaded-mod4.c @@ -0,0 +1,25 @@ +/* Test support for single-thread optimizations. Shared object 4. + Copyright (C) 2019 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 + . */ + +#include + +_Bool +single_threaded_4 (void) +{ + return __libc_single_threaded; +} diff --git a/elf/tst-single_threaded-pthread-static.c b/elf/tst-single_threaded-pthread-static.c new file mode 100644 index 0000000000..780564c40c --- /dev/null +++ b/elf/tst-single_threaded-pthread-static.c @@ -0,0 +1,86 @@ +/* Test support for single-thread optimizations. With threads, static version. + Copyright (C) 2019 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 + . */ + +/* This test is a stripped-down version of + tst-single_threaded-pthread.c, without any loading of dynamic + objects. */ + +#include +#include +#include +#include + +/* First barrier synchronizes main thread, thread 1, thread 2. */ +static pthread_barrier_t barrier1; + +/* Second barrier synchronizes main thread, thread 2. */ +static pthread_barrier_t barrier2; + +static void * +threadfunc (void *closure) +{ + TEST_VERIFY (!__libc_single_threaded); + + /* Wait for the main thread and the other thread. */ + xpthread_barrier_wait (&barrier1); + TEST_VERIFY (!__libc_single_threaded); + + /* Second thread waits on second barrier, too. */ + if (closure != NULL) + xpthread_barrier_wait (&barrier2); + TEST_VERIFY (!__libc_single_threaded); + + return NULL; +} + +static int +do_test (void) +{ + TEST_VERIFY (__libc_single_threaded); + + /* Two threads plus main thread. */ + xpthread_barrier_init (&barrier1, NULL, 3); + + /* Main thread and second thread. */ + xpthread_barrier_init (&barrier2, NULL, 2); + + pthread_t thr1 = xpthread_create (NULL, threadfunc, NULL); + TEST_VERIFY (!__libc_single_threaded); + + pthread_t thr2 = xpthread_create (NULL, threadfunc, &thr2); + TEST_VERIFY (!__libc_single_threaded); + + xpthread_barrier_wait (&barrier1); + TEST_VERIFY (!__libc_single_threaded); + + /* Join first thread. This should not bring us back into + single-threaded mode. */ + xpthread_join (thr1); + TEST_VERIFY (!__libc_single_threaded); + + /* We may be back in single-threaded mode after joining both + threads, but this is not guaranteed. */ + xpthread_barrier_wait (&barrier2); + xpthread_join (thr2); + printf ("info: __libc_single_threaded after joining all threads: %d\n", + __libc_single_threaded); + + return 0; +} + +#include diff --git a/elf/tst-single_threaded-pthread.c b/elf/tst-single_threaded-pthread.c new file mode 100644 index 0000000000..c02f4047d1 --- /dev/null +++ b/elf/tst-single_threaded-pthread.c @@ -0,0 +1,174 @@ +/* Test support for single-thread optimizations. With threads. + Copyright (C) 2019 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 + . */ + +#include +#include +#include +#include +#include +#include +#include + +/* First barrier synchronizes main thread, thread 1, thread 2. */ +static pthread_barrier_t barrier1; + +/* Second barrier synchronizes main thread, thread 2. */ +static pthread_barrier_t barrier2; + +/* Defined in tst-single-threaded-mod1.so. */ +_Bool single_threaded_1 (void); + +/* Initialized via dlsym. */ +static _Bool (*single_threaded_2) (void); +static _Bool (*single_threaded_3) (void); +static _Bool (*single_threaded_4) (void); + +static void * +threadfunc (void *closure) +{ + TEST_VERIFY (!__libc_single_threaded); + TEST_VERIFY (!single_threaded_1 ()); + TEST_VERIFY (!single_threaded_2 ()); + + /* Wait until the main thread loads more functions. */ + xpthread_barrier_wait (&barrier1); + + TEST_VERIFY (!__libc_single_threaded); + TEST_VERIFY (!single_threaded_1 ()); + TEST_VERIFY (!single_threaded_2 ()); + TEST_VERIFY (!single_threaded_3 ()); + TEST_VERIFY (!single_threaded_4 ()); + + /* Second thread waits on second barrier, too. */ + if (closure != NULL) + xpthread_barrier_wait (&barrier2); + TEST_VERIFY (!__libc_single_threaded); + TEST_VERIFY (!single_threaded_1 ()); + TEST_VERIFY (!single_threaded_2 ()); + TEST_VERIFY (!single_threaded_3 ()); + TEST_VERIFY (!single_threaded_4 ()); + + return NULL; +} + +/* Used for closure arguments to the subprocess function. */ +static char expected_false = 0; +static char expected_true = 1; + +/* A subprocess inherits currently inherits the single-threaded state + of the parent process. */ +static void +subprocess (void *closure) +{ + const char *expected = closure; + TEST_COMPARE (__libc_single_threaded, *expected); + TEST_COMPARE (single_threaded_1 (), *expected); + if (single_threaded_2 != NULL) + TEST_COMPARE (single_threaded_2 (), *expected); + if (single_threaded_3 != NULL) + TEST_COMPARE (single_threaded_3 (), *expected); + if (single_threaded_4 != NULL) + TEST_VERIFY (!single_threaded_4 ()); +} + +static int +do_test (void) +{ + printf ("info: main __libc_single_threaded address: %p\n", + &__libc_single_threaded); + TEST_VERIFY (__libc_single_threaded); + TEST_VERIFY (single_threaded_1 ()); + support_isolate_in_subprocess (subprocess, &expected_true); + + void *handle_mod2 = xdlopen ("tst-single_threaded-mod2.so", RTLD_LAZY); + single_threaded_2 = xdlsym (handle_mod2, "single_threaded_2"); + TEST_VERIFY (single_threaded_2 ()); + + /* Two threads plus main thread. */ + xpthread_barrier_init (&barrier1, NULL, 3); + + /* Main thread and second thread. */ + xpthread_barrier_init (&barrier2, NULL, 2); + + pthread_t thr1 = xpthread_create (NULL, threadfunc, NULL); + TEST_VERIFY (!__libc_single_threaded); + TEST_VERIFY (!single_threaded_1 ()); + TEST_VERIFY (!single_threaded_2 ()); + support_isolate_in_subprocess (subprocess, &expected_false); + + pthread_t thr2 = xpthread_create (NULL, threadfunc, &thr2); + TEST_VERIFY (!__libc_single_threaded); + TEST_VERIFY (!single_threaded_1 ()); + TEST_VERIFY (!single_threaded_2 ()); + support_isolate_in_subprocess (subprocess, &expected_false); + + /* Delayed library load, while already multi-threaded. */ + void *handle_mod3 = xdlopen ("tst-single_threaded-mod3.so", RTLD_LAZY); + single_threaded_3 = xdlsym (handle_mod3, "single_threaded_3"); + TEST_VERIFY (!__libc_single_threaded); + TEST_VERIFY (!single_threaded_1 ()); + TEST_VERIFY (!single_threaded_2 ()); + TEST_VERIFY (!single_threaded_3 ()); + support_isolate_in_subprocess (subprocess, &expected_false); + + /* Same with dlmopen. */ + void *handle_mod4 = dlmopen (LM_ID_NEWLM, "tst-single_threaded-mod4.so", + RTLD_LAZY); + single_threaded_4 = xdlsym (handle_mod4, "single_threaded_4"); + TEST_VERIFY (!__libc_single_threaded); + TEST_VERIFY (!single_threaded_1 ()); + TEST_VERIFY (!single_threaded_2 ()); + TEST_VERIFY (!single_threaded_3 ()); + TEST_VERIFY (!single_threaded_4 ()); + support_isolate_in_subprocess (subprocess, &expected_false); + + /* Run the newly loaded functions from the other threads as + well. */ + xpthread_barrier_wait (&barrier1); + TEST_VERIFY (!__libc_single_threaded); + TEST_VERIFY (!single_threaded_1 ()); + TEST_VERIFY (!single_threaded_2 ()); + TEST_VERIFY (!single_threaded_3 ()); + TEST_VERIFY (!single_threaded_4 ()); + support_isolate_in_subprocess (subprocess, &expected_false); + + /* Join first thread. This should not bring us back into + single-threaded mode. */ + xpthread_join (thr1); + TEST_VERIFY (!__libc_single_threaded); + TEST_VERIFY (!single_threaded_1 ()); + TEST_VERIFY (!single_threaded_2 ()); + TEST_VERIFY (!single_threaded_3 ()); + TEST_VERIFY (!single_threaded_4 ()); + support_isolate_in_subprocess (subprocess, &expected_false); + + /* We may be back in single-threaded mode after joining both + threads, but this is not guaranteed. */ + xpthread_barrier_wait (&barrier2); + xpthread_join (thr2); + printf ("info: __libc_single_threaded after joining all threads: %d\n", + __libc_single_threaded); + + xdlclose (handle_mod4); + xdlclose (handle_mod3); + xdlclose (handle_mod2); + + return 0; +} + +#include diff --git a/elf/tst-single_threaded-static-dlopen.c b/elf/tst-single_threaded-static-dlopen.c new file mode 100644 index 0000000000..f270cf452e --- /dev/null +++ b/elf/tst-single_threaded-static-dlopen.c @@ -0,0 +1,56 @@ +/* Test support for single-thread optimizations. No threads, static dlopen. + Copyright (C) 2019 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 + . */ + +/* In a static dlopen scenario, the single-threaded optimization is + not possible because their is no globally shared dynamic linker + across all namespaces. */ + +#include +#include +#include +#include + +static int +do_test (void) +{ + TEST_VERIFY (__libc_single_threaded); + + /* Defined in tst-single-threaded-mod1.o. */ + extern _Bool single_threaded_1 (void); + TEST_VERIFY (single_threaded_1 ()); + + /* Even after a failed dlopen, assume multi-threaded mode. */ + TEST_VERIFY (dlopen ("tst-single_threaded-does-not-exist.so", RTLD_LAZY) + == NULL); + TEST_VERIFY (__libc_single_threaded); + TEST_VERIFY (single_threaded_1 ()); + + void *handle_mod2 = xdlopen ("tst-single_threaded-mod2.so", RTLD_LAZY); + _Bool (*single_threaded_2) (void) + = xdlsym (handle_mod2, "single_threaded_2"); + TEST_VERIFY (__libc_single_threaded); + TEST_VERIFY (single_threaded_1 ()); + /* The inner libc always assumes multi-threaded use. */ + TEST_VERIFY (!single_threaded_2 ()); + + xdlclose (handle_mod2); + + return 0; +} + +#include diff --git a/elf/tst-single_threaded-static.c b/elf/tst-single_threaded-static.c new file mode 100644 index 0000000000..29d7ab2731 --- /dev/null +++ b/elf/tst-single_threaded-static.c @@ -0,0 +1,29 @@ +/* Test support for single-thread optimizations. Static, no threads. + Copyright (C) 2019 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 + . */ + +#include +#include + +static int +do_test (void) +{ + TEST_VERIFY (__libc_single_threaded); + return 0; +} + +#include diff --git a/elf/tst-single_threaded.c b/elf/tst-single_threaded.c new file mode 100644 index 0000000000..478c2dc259 --- /dev/null +++ b/elf/tst-single_threaded.c @@ -0,0 +1,70 @@ +/* Test support for single-thread optimizations. No threads. + Copyright (C) 2020 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 + . */ + +#include +#include +#include +#include +#include +#include + +/* Defined in tst-single-threaded-mod1.so. */ +extern _Bool single_threaded_1 (void); + +/* Initialized via dlsym. */ +_Bool (*single_threaded_2) (void); +_Bool (*single_threaded_3) (void); + +static void +subprocess (void *closure) +{ + TEST_VERIFY (__libc_single_threaded); + TEST_VERIFY (single_threaded_1 ()); + if (single_threaded_2 != NULL) + TEST_VERIFY (single_threaded_2 ()); + if (single_threaded_3 != NULL) + TEST_VERIFY (!single_threaded_3 ()); +} + +static int +do_test (void) +{ + TEST_VERIFY (__libc_single_threaded); + TEST_VERIFY (single_threaded_1 ()); + support_isolate_in_subprocess (subprocess, NULL); + + void *handle_mod2 = xdlopen ("tst-single_threaded-mod2.so", RTLD_LAZY); + single_threaded_2 = xdlsym (handle_mod2, "single_threaded_2"); + TEST_VERIFY (single_threaded_2 ()); + support_isolate_in_subprocess (subprocess, NULL); + + /* The current implementation treats the inner namespace as + multi-threaded. */ + void *handle_mod3 = dlmopen (LM_ID_NEWLM, "tst-single_threaded-mod3.so", + RTLD_LAZY); + single_threaded_3 = xdlsym (handle_mod3, "single_threaded_3"); + TEST_VERIFY (!single_threaded_3 ()); + support_isolate_in_subprocess (subprocess, NULL); + + xdlclose (handle_mod3); + xdlclose (handle_mod2); + + return 0; +} + +#include diff --git a/htl/pt-create.c b/htl/pt-create.c index f501a12017..7ac875cbf7 100644 --- a/htl/pt-create.c +++ b/htl/pt-create.c @@ -24,6 +24,7 @@ #include #include +#include #include #include @@ -104,6 +105,10 @@ __pthread_create_internal (struct __pthread **thread, sigset_t sigset; size_t stacksize; + /* Avoid a data race in the multi-threaded case. */ + if (__libc_single_threaded) + __libc_single_threaded = 0; + /* Allocate a new thread structure. */ err = __pthread_alloc (&pthread); if (err) diff --git a/include/sys/single_threaded.h b/include/sys/single_threaded.h new file mode 100644 index 0000000000..18f6972482 --- /dev/null +++ b/include/sys/single_threaded.h @@ -0,0 +1 @@ +#include diff --git a/misc/Makefile b/misc/Makefile index 67c5237f97..58959f6913 100644 --- a/misc/Makefile +++ b/misc/Makefile @@ -37,7 +37,8 @@ headers := sys/uio.h bits/uio-ext.h bits/uio_lim.h \ bits/syslog.h bits/syslog-ldbl.h bits/syslog-path.h bits/error.h \ bits/select2.h bits/hwcap.h sys/auxv.h \ sys/sysmacros.h bits/sysmacros.h bits/types/struct_iovec.h \ - bits/err-ldbl.h bits/error-ldbl.h + bits/err-ldbl.h bits/error-ldbl.h \ + sys/single_threaded.h routines := brk sbrk sstk ioctl \ readv writev preadv preadv64 pwritev pwritev64 \ @@ -72,7 +73,7 @@ routines := brk sbrk sstk ioctl \ fgetxattr flistxattr fremovexattr fsetxattr getxattr \ listxattr lgetxattr llistxattr lremovexattr lsetxattr \ removexattr setxattr getauxval ifunc-impl-list makedev \ - allocate_once fd_to_filename + allocate_once fd_to_filename single_threaded generated += tst-error1.mtrace tst-error1-mem.out \ tst-allocate_once.mtrace tst-allocate_once-mem.out diff --git a/misc/Versions b/misc/Versions index e749582369..95666f6548 100644 --- a/misc/Versions +++ b/misc/Versions @@ -161,6 +161,9 @@ libc { GLIBC_2.30 { twalk_r; } + GLIBC_2.32 { + __libc_single_threaded; + } GLIBC_PRIVATE { __madvise; __mktemp; diff --git a/misc/single_threaded.c b/misc/single_threaded.c new file mode 100644 index 0000000000..d7c55b784b --- /dev/null +++ b/misc/single_threaded.c @@ -0,0 +1,27 @@ +/* Support for single-thread optimizations. Statically linked version. + Copyright (C) 2019 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 + . */ + +#include + +/* In dynamically linked programs, this variable is initialized in + __libc_early_init (as false for inner libcs). */ +#ifdef SHARED +char __libc_single_threaded; +#else +char __libc_single_threaded = 1; +#endif diff --git a/misc/sys/single_threaded.h b/misc/sys/single_threaded.h new file mode 100644 index 0000000000..c721141d35 --- /dev/null +++ b/misc/sys/single_threaded.h @@ -0,0 +1,33 @@ +/* Support for single-thread optimizations. + Copyright (C) 2019 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 + . */ + +#ifndef _SYS_SINGLE_THREADED_H +#define _SYS_SINGLE_THREADED_H + +#include + +__BEGIN_DECLS + +/* If this variable is non-zero, then the current thread is the only + thread in the process image. If it is zero, the process can be + multi-threaded. */ +extern char __libc_single_threaded; + +__END_DECLS + +#endif /* _SYS_SINGLE_THREADED_H */ diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c index a43089065c..6fffe07ffa 100644 --- a/nptl/pthread_create.c +++ b/nptl/pthread_create.c @@ -34,6 +34,7 @@ #include #include #include "libioP.h" +#include #include @@ -611,6 +612,10 @@ __pthread_create_2_1 (pthread_t *newthread, const pthread_attr_t *attr, { STACK_VARIABLES; + /* Avoid a data race in the multi-threaded case. */ + if (__libc_single_threaded) + __libc_single_threaded = 0; + const struct pthread_attr *iattr = (struct pthread_attr *) attr; struct pthread_attr default_attr; bool free_cpuset = false; diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h index 5ff4a2831b..fa5c200f73 100644 --- a/sysdeps/generic/ldsodefs.h +++ b/sysdeps/generic/ldsodefs.h @@ -482,9 +482,11 @@ struct rtld_global # define __rtld_local_attribute__ __attribute__ ((visibility ("hidden"))) # endif extern struct rtld_global _rtld_local __rtld_local_attribute__; +extern char __libc_single_threaded_local __rtld_local_attribute__; # undef __rtld_local_attribute__ # endif extern struct rtld_global _rtld_global __rtld_global_attribute__; +extern char __libc_single_threaded __rtld_global_attribute__; # undef __rtld_global_attribute__ #endif @@ -1124,6 +1126,9 @@ extern struct link_map * _dl_get_dl_main_map (void) If libpthread is not linked in, this is an empty function. */ void __pthread_initialize_minimal (void) weak_function; +/* Update both copies of __libc_single_threaded. */ +void _dl_single_threaded_update (char value); + /* Allocate memory for static TLS block (unless MEM is nonzero) and dtv. */ extern void *_dl_allocate_tls (void *mem); rtld_hidden_proto (_dl_allocate_tls) diff --git a/sysdeps/generic/libc.abilist b/sysdeps/generic/libc.abilist index e69de29bb2..8ca9b93c2f 100644 --- a/sysdeps/generic/libc.abilist +++ b/sysdeps/generic/libc.abilist @@ -0,0 +1 @@ +GLIBC_2.32 __libc_single_threaded D 0x1 diff --git a/sysdeps/mach/hurd/i386/libc.abilist b/sysdeps/mach/hurd/i386/libc.abilist index 60696d827f..67a98ae86f 100644 --- a/sysdeps/mach/hurd/i386/libc.abilist +++ b/sysdeps/mach/hurd/i386/libc.abilist @@ -2181,6 +2181,7 @@ GLIBC_2.3.4 setsourcefilter F GLIBC_2.3.4 xdr_quad_t F GLIBC_2.3.4 xdr_u_quad_t F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 mach_print F GLIBC_2.32 thrd_current F GLIBC_2.32 thrd_equal F diff --git a/sysdeps/unix/sysv/linux/aarch64/libc.abilist b/sysdeps/unix/sysv/linux/aarch64/libc.abilist index 41bb214bb9..c526f8d661 100644 --- a/sysdeps/unix/sysv/linux/aarch64/libc.abilist +++ b/sysdeps/unix/sysv/linux/aarch64/libc.abilist @@ -2146,4 +2146,5 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F diff --git a/sysdeps/unix/sysv/linux/alpha/libc.abilist b/sysdeps/unix/sysv/linux/alpha/libc.abilist index 6430af207f..cdc5c27fa9 100644 --- a/sysdeps/unix/sysv/linux/alpha/libc.abilist +++ b/sysdeps/unix/sysv/linux/alpha/libc.abilist @@ -2226,6 +2226,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 _IO_fprintf F GLIBC_2.4 _IO_printf F diff --git a/sysdeps/unix/sysv/linux/arm/be/libc.abilist b/sysdeps/unix/sysv/linux/arm/be/libc.abilist index f4ea1756d5..18c6901a47 100644 --- a/sysdeps/unix/sysv/linux/arm/be/libc.abilist +++ b/sysdeps/unix/sysv/linux/arm/be/libc.abilist @@ -133,6 +133,7 @@ GLIBC_2.30 twalk_r F GLIBC_2.31 msgctl F GLIBC_2.31 semctl F GLIBC_2.31 shmctl F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 _Exit F GLIBC_2.4 _IO_2_1_stderr_ D 0xa0 diff --git a/sysdeps/unix/sysv/linux/arm/le/libc.abilist b/sysdeps/unix/sysv/linux/arm/le/libc.abilist index f1456b26b2..f3bfff868b 100644 --- a/sysdeps/unix/sysv/linux/arm/le/libc.abilist +++ b/sysdeps/unix/sysv/linux/arm/le/libc.abilist @@ -130,6 +130,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 _Exit F GLIBC_2.4 _IO_2_1_stderr_ D 0xa0 diff --git a/sysdeps/unix/sysv/linux/csky/libc.abilist b/sysdeps/unix/sysv/linux/csky/libc.abilist index c54aed2f8e..d61457aef0 100644 --- a/sysdeps/unix/sysv/linux/csky/libc.abilist +++ b/sysdeps/unix/sysv/linux/csky/libc.abilist @@ -2090,4 +2090,5 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F diff --git a/sysdeps/unix/sysv/linux/hppa/libc.abilist b/sysdeps/unix/sysv/linux/hppa/libc.abilist index 87373f755b..b9e28741eb 100644 --- a/sysdeps/unix/sysv/linux/hppa/libc.abilist +++ b/sysdeps/unix/sysv/linux/hppa/libc.abilist @@ -2047,6 +2047,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 __confstr_chk F GLIBC_2.4 __fgets_chk F diff --git a/sysdeps/unix/sysv/linux/i386/libc.abilist b/sysdeps/unix/sysv/linux/i386/libc.abilist index 1bd2e02f79..ae74842837 100644 --- a/sysdeps/unix/sysv/linux/i386/libc.abilist +++ b/sysdeps/unix/sysv/linux/i386/libc.abilist @@ -2213,6 +2213,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 __confstr_chk F GLIBC_2.4 __fgets_chk F diff --git a/sysdeps/unix/sysv/linux/ia64/libc.abilist b/sysdeps/unix/sysv/linux/ia64/libc.abilist index 07e51d46bf..b7190f60f6 100644 --- a/sysdeps/unix/sysv/linux/ia64/libc.abilist +++ b/sysdeps/unix/sysv/linux/ia64/libc.abilist @@ -2079,6 +2079,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 __confstr_chk F GLIBC_2.4 __fgets_chk F diff --git a/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist b/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist index 42ea4c24bf..48ab675319 100644 --- a/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist +++ b/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist @@ -134,6 +134,7 @@ GLIBC_2.30 twalk_r F GLIBC_2.31 msgctl F GLIBC_2.31 semctl F GLIBC_2.31 shmctl F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 _Exit F GLIBC_2.4 _IO_2_1_stderr_ D 0x98 diff --git a/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist b/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist index e9358fb092..125d98b17c 100644 --- a/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist +++ b/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist @@ -2159,6 +2159,7 @@ GLIBC_2.30 twalk_r F GLIBC_2.31 msgctl F GLIBC_2.31 semctl F GLIBC_2.31 shmctl F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 __confstr_chk F GLIBC_2.4 __fgets_chk F diff --git a/sysdeps/unix/sysv/linux/microblaze/be/libc.abilist b/sysdeps/unix/sysv/linux/microblaze/be/libc.abilist index 2cefe739c0..d40ead85d2 100644 --- a/sysdeps/unix/sysv/linux/microblaze/be/libc.abilist +++ b/sysdeps/unix/sysv/linux/microblaze/be/libc.abilist @@ -2141,4 +2141,5 @@ GLIBC_2.30 twalk_r F GLIBC_2.31 msgctl F GLIBC_2.31 semctl F GLIBC_2.31 shmctl F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F diff --git a/sysdeps/unix/sysv/linux/microblaze/le/libc.abilist b/sysdeps/unix/sysv/linux/microblaze/le/libc.abilist index 3474ef1490..fcca528d68 100644 --- a/sysdeps/unix/sysv/linux/microblaze/le/libc.abilist +++ b/sysdeps/unix/sysv/linux/microblaze/le/libc.abilist @@ -2138,4 +2138,5 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F diff --git a/sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist b/sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist index a6f99a7369..42a5cd5d08 100644 --- a/sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist +++ b/sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist @@ -2130,6 +2130,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 __confstr_chk F GLIBC_2.4 __fgets_chk F diff --git a/sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist b/sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist index 48222af11c..eef6cdc23f 100644 --- a/sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist +++ b/sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist @@ -2128,6 +2128,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 __confstr_chk F GLIBC_2.4 __fgets_chk F diff --git a/sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist b/sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist index 99965cfb0f..3d970ddd0a 100644 --- a/sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist +++ b/sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist @@ -2136,6 +2136,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 __confstr_chk F GLIBC_2.4 __fgets_chk F diff --git a/sysdeps/unix/sysv/linux/mips/mips64/n64/libc.abilist b/sysdeps/unix/sysv/linux/mips/mips64/n64/libc.abilist index 2c8bafc669..5050f84b5d 100644 --- a/sysdeps/unix/sysv/linux/mips/mips64/n64/libc.abilist +++ b/sysdeps/unix/sysv/linux/mips/mips64/n64/libc.abilist @@ -2130,6 +2130,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 __confstr_chk F GLIBC_2.4 __fgets_chk F diff --git a/sysdeps/unix/sysv/linux/nios2/libc.abilist b/sysdeps/unix/sysv/linux/nios2/libc.abilist index 52cf72052c..7523f06805 100644 --- a/sysdeps/unix/sysv/linux/nios2/libc.abilist +++ b/sysdeps/unix/sysv/linux/nios2/libc.abilist @@ -2179,4 +2179,5 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libc.abilist b/sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libc.abilist index 2ca5bbccf3..a9b169bf79 100644 --- a/sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libc.abilist +++ b/sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libc.abilist @@ -2186,6 +2186,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 _IO_fprintf F GLIBC_2.4 _IO_printf F diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libc.abilist b/sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libc.abilist index e6c4d002d5..59218e2188 100644 --- a/sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libc.abilist +++ b/sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libc.abilist @@ -2219,6 +2219,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 _IO_fprintf F GLIBC_2.4 _IO_printf F diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc64/be/libc.abilist b/sysdeps/unix/sysv/linux/powerpc/powerpc64/be/libc.abilist index 82d77b7e48..f06a8add0e 100644 --- a/sysdeps/unix/sysv/linux/powerpc/powerpc64/be/libc.abilist +++ b/sysdeps/unix/sysv/linux/powerpc/powerpc64/be/libc.abilist @@ -2049,6 +2049,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 _IO_fprintf F GLIBC_2.4 _IO_printf F diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc64/le/libc.abilist b/sysdeps/unix/sysv/linux/powerpc/powerpc64/le/libc.abilist index 0c2513a4b3..ac57ac82e3 100644 --- a/sysdeps/unix/sysv/linux/powerpc/powerpc64/le/libc.abilist +++ b/sysdeps/unix/sysv/linux/powerpc/powerpc64/le/libc.abilist @@ -2276,6 +2276,7 @@ GLIBC_2.32 __isoc99_vsscanfieee128 F GLIBC_2.32 __isoc99_vswscanfieee128 F GLIBC_2.32 __isoc99_vwscanfieee128 F GLIBC_2.32 __isoc99_wscanfieee128 F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 __obstack_printf_chkieee128 F GLIBC_2.32 __obstack_printfieee128 F GLIBC_2.32 __obstack_vprintf_chkieee128 F diff --git a/sysdeps/unix/sysv/linux/riscv/rv64/libc.abilist b/sysdeps/unix/sysv/linux/riscv/rv64/libc.abilist index 234d34929a..128c040b7f 100644 --- a/sysdeps/unix/sysv/linux/riscv/rv64/libc.abilist +++ b/sysdeps/unix/sysv/linux/riscv/rv64/libc.abilist @@ -2108,4 +2108,5 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F diff --git a/sysdeps/unix/sysv/linux/s390/s390-32/libc.abilist b/sysdeps/unix/sysv/linux/s390/s390-32/libc.abilist index 1f06cce028..3881fe4e77 100644 --- a/sysdeps/unix/sysv/linux/s390/s390-32/libc.abilist +++ b/sysdeps/unix/sysv/linux/s390/s390-32/libc.abilist @@ -2184,6 +2184,7 @@ GLIBC_2.30 twalk_r F GLIBC_2.31 msgctl F GLIBC_2.31 semctl F GLIBC_2.31 shmctl F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 _IO_fprintf F GLIBC_2.4 _IO_printf F diff --git a/sysdeps/unix/sysv/linux/s390/s390-64/libc.abilist b/sysdeps/unix/sysv/linux/s390/s390-64/libc.abilist index 26c2ce32e5..d62589c337 100644 --- a/sysdeps/unix/sysv/linux/s390/s390-64/libc.abilist +++ b/sysdeps/unix/sysv/linux/s390/s390-64/libc.abilist @@ -2085,6 +2085,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 _IO_fprintf F GLIBC_2.4 _IO_printf F diff --git a/sysdeps/unix/sysv/linux/sh/be/libc.abilist b/sysdeps/unix/sysv/linux/sh/be/libc.abilist index 7ad2e920c3..df4abe3400 100644 --- a/sysdeps/unix/sysv/linux/sh/be/libc.abilist +++ b/sysdeps/unix/sysv/linux/sh/be/libc.abilist @@ -2054,6 +2054,7 @@ GLIBC_2.30 twalk_r F GLIBC_2.31 msgctl F GLIBC_2.31 semctl F GLIBC_2.31 shmctl F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 __confstr_chk F GLIBC_2.4 __fgets_chk F diff --git a/sysdeps/unix/sysv/linux/sh/le/libc.abilist b/sysdeps/unix/sysv/linux/sh/le/libc.abilist index d2611bf0a5..a4d69cae90 100644 --- a/sysdeps/unix/sysv/linux/sh/le/libc.abilist +++ b/sysdeps/unix/sysv/linux/sh/le/libc.abilist @@ -2051,6 +2051,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 __confstr_chk F GLIBC_2.4 __fgets_chk F diff --git a/sysdeps/unix/sysv/linux/sparc/sparc32/libc.abilist b/sysdeps/unix/sysv/linux/sparc/sparc32/libc.abilist index 18a528f0e9..b5dfc8582f 100644 --- a/sysdeps/unix/sysv/linux/sparc/sparc32/libc.abilist +++ b/sysdeps/unix/sysv/linux/sparc/sparc32/libc.abilist @@ -2175,6 +2175,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 _IO_fprintf F GLIBC_2.4 _IO_printf F diff --git a/sysdeps/unix/sysv/linux/sparc/sparc64/libc.abilist b/sysdeps/unix/sysv/linux/sparc/sparc64/libc.abilist index a1d48b0f3c..7f8c73735b 100644 --- a/sysdeps/unix/sysv/linux/sparc/sparc64/libc.abilist +++ b/sysdeps/unix/sysv/linux/sparc/sparc64/libc.abilist @@ -2102,6 +2102,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 __confstr_chk F GLIBC_2.4 __fgets_chk F diff --git a/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist b/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist index 6418ace78a..4484052d63 100644 --- a/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist +++ b/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist @@ -2060,6 +2060,7 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F GLIBC_2.4 __confstr_chk F GLIBC_2.4 __fgets_chk F diff --git a/sysdeps/unix/sysv/linux/x86_64/x32/libc.abilist b/sysdeps/unix/sysv/linux/x86_64/x32/libc.abilist index edb9f2f004..b36a994d39 100644 --- a/sysdeps/unix/sysv/linux/x86_64/x32/libc.abilist +++ b/sysdeps/unix/sysv/linux/x86_64/x32/libc.abilist @@ -2159,4 +2159,5 @@ GLIBC_2.30 getdents64 F GLIBC_2.30 gettid F GLIBC_2.30 tgkill F GLIBC_2.30 twalk_r F +GLIBC_2.32 __libc_single_threaded D 0x1 GLIBC_2.32 pthread_sigmask F From patchwork Wed May 20 18:12:59 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 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__libc_single_threaded In-Reply-To: References: Message-Id: <2c218c9ed9586ed5491f6fa08045d1e883b126c3.1589998207.git.fweimer@redhat.com> Date: Wed, 20 May 2020 20:12:59 +0200 User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-Spam-Status: No, score=-14.0 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2, 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-Patchwork-Original-From: Florian Weimer via Libc-alpha From: Florian Weimer Reply-To: Florian Weimer Cc: Michael Kerrisk Errors-To: libc-alpha-bounces@sourceware.org Sender: "Libc-alpha" --- manual/threads.texi | 89 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 89 insertions(+) diff --git a/manual/threads.texi b/manual/threads.texi index a425635179..d4c261a0e9 100644 --- a/manual/threads.texi +++ b/manual/threads.texi @@ -627,6 +627,7 @@ the standard. threads in a process. * Waiting with Explicit Clocks:: Functions for waiting with an explicit clock specification. +* Single-Threaded:: Detecting single-threaded execution. @end menu @node Default Thread Attributes @@ -771,6 +772,94 @@ Behaves like @code{pthread_timedjoin_np} except that the absolute time in @var{abstime} is measured against the clock specified by @var{clockid}. @end deftypefun +@node Single-Threaded +@subsubsection Detecting Single-Threaded Execution + +Multi-threaded programs require synchronization among threads. This +synchronization can be costly even if there is just a single thread +and no data is shared between multiple processors. @Theglibc{} offers +an interface to detect whether the process is in single-threaded mode. +Applications can use this information to avoid synchronization, for +example by using regular instructions to load and store memory instead +of atomic instructions, or using relaxed memory ordering instead of +stronger memory ordering. + +@deftypevar char __libc_single_threaded +@standards{GNU, sys/single_threaded.h} +This variable is non-zero if the current process is definitely +single-threaded. If it is zero, the process can be multi-threaded, +or @theglibc{} cannot determine at this point of the program execution +whether the process is single-threaded or not. + +Applications must never write to this variable. +@end deftypevar + +Most applications should perform the same actions whether or not +@code{__libc_single_threaded} is true, except with less +synchronization. If this rule is followed, a process that +subsequently becomes multi-threaded is already in a consistent state. +For example, in order to increment a reference count, the following +code can be used: + +@smallexample +if (__libc_single_threaded) + atomic_fetch_add (&reference_count, 1, memory_order_relaxed); +else + atomic_fetch_add (&reference_count, 1, memory_order_acq_rel); +@end smallexample + +This still requires some form of synchronization on the +single-threaded branch, so it can be beneficial not to declare the +reference count as @code{_Atomic}, and use the GCC @code{__atomic} +built-ins. @xref{__atomic Builtins,, Built-in Functions for Memory +Model Aware Atomic Operations, gcc, Using the GNU Compiler Collection +(GCC)}. Then the code to increment a reference count looks like this: + +@smallexample +if (__libc_single_threaded) + ++refeference_count;inf +else + __atomic_fetch_add (&reference_count, 1, __ATOMIC_ACQ_REL); +@end smallexample + +(Depending on the data associated with the reference count, it may be +possible to use the weaker @code{__ATOMIC_RELAXED} memory ordering on +the multi-threaded branch.) + +Several functions in @theglibc{} can change the value of the +@code{__libc_single_threaded} variable. For example, creating new +threads using the @code{pthread_create} or @code{thrd_create} function +sets the variable to false. This can also happen directly, say via a +call to @code{dlopen}. Therefore, applications need to make a copy of +the value of @code{__libc_single_threaded} if after such a function +call, behavior must match the value as it was before the call, like +this: + +@smallexample +bool single_threaded = __libc_single_threaded; +if (single_threaded) + prepare_single_threaded (); +else + prepare_multi_thread (); + +void *handle = dlopen (shared_library_name, RTLD_NOW); +lookup_symbols (handle); + +if (single_threaded) + cleanup_single_threaded (); +else + cleanup_multi_thread (); +@end smallexample + +Since the value of @code{__libc_single_threaded} can change from true +to false during the execution of the program, it is not useful for +selecting optimized function implementations in IFUNC resolvers. + +Atomic operations can also be used on mappings shared among +single-threaded processes. This means that a compiler cannot use +@code{__libc_single_threaded} to optimize atomic operations, unless it +is able to prove that the memory is not shared. + @c FIXME these are undocumented: @c pthread_atfork @c pthread_attr_destroy