From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id EB40E385734C for ; Tue, 16 May 2023 17:32:01 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org EB40E385734C Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1684258321; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=Zpz1M8ZMp5WVAj94+4zKuHJ2dG8qYD2hQpzQcAYKBlY=; b=deDfmE0SolQNcZvlpksjuHPnqZgvHrRX8G7rDyM9AeborMdwKiyT0qtEb9BxJHlN/5WTku PYHLVexHWP+ijWac46nI1SY1TqgGukQr7FpgaOOreg5viAGXFihy4s98A3sB+GkfhRQ+tg Y3dplRnKm6Cs0a+qtfoJQqdh1FVMg94= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-369-lALqYCMyOA6CUlGeGLlBiw-1; Tue, 16 May 2023 13:31:58 -0400 X-MC-Unique: lALqYCMyOA6CUlGeGLlBiw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 25EF538294A9; Tue, 16 May 2023 17:31:58 +0000 (UTC) Received: from localhost (unknown [10.42.28.178]) by smtp.corp.redhat.com (Postfix) with ESMTP id DE97F1121314; Tue, 16 May 2023 17:31:57 +0000 (UTC) From: Jonathan Wakely To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Subject: [committed] libstdc++: Disable cacheline alignment for DJGPP [PR109741] Date: Tue, 16 May 2023 18:31:56 +0100 Message-Id: <20230516173156.1826089-1-jwakely@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-12.1 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,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Tested powerpc64le-linux. Builds OK on djgpp too. Pushed to trunk. -- >8 -- DJGPP (and maybe other targets) uses MAX_OFILE_ALIGNMENT=16 which means that globals (and static objects) can't have alignment greater than 16. This causes an error for the locks defined in src/c++11/shared_ptr.cc because we try to align them to the cacheline size, to avoid false sharing. Add a configure check for the increased alignment, and live with false sharing where we can't increase the alignment. libstdc++-v3/ChangeLog: PR libstdc++/109741 * acinclude.m4 (GLIBCXX_CHECK_ALIGNAS_CACHELINE): Define. * config.h.in: Regenerate. * configure: Regenerate. * configure.ac: Use GLIBCXX_CHECK_ALIGNAS_CACHELINE. * src/c++11/shared_ptr.cc (__gnu_internal::get_mutex): Do not align lock table if not supported. use __GCC_DESTRUCTIVE_SIZE instead of hardcoded 64. --- libstdc++-v3/acinclude.m4 | 25 +++++++++++++++ libstdc++-v3/config.h.in | 4 +++ libstdc++-v3/configure | 48 ++++++++++++++++++++++++++++ libstdc++-v3/configure.ac | 3 ++ libstdc++-v3/src/c++11/shared_ptr.cc | 8 +++-- 5 files changed, 86 insertions(+), 2 deletions(-) diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4 index 988c532c4e2..8129373e9dd 100644 --- a/libstdc++-v3/acinclude.m4 +++ b/libstdc++-v3/acinclude.m4 @@ -5471,6 +5471,31 @@ AC_DEFUN([GLIBCXX_ZONEINFO_DIR], [ fi ]) +dnl +dnl Check whether lock tables can be aligned to avoid false sharing. +dnl +dnl Defines: +dnl _GLIBCXX_CAN_ALIGNAS_DESTRUCTIVE_SIZE if objects with static storage +dnl duration can be aligned to std::hardware_destructive_interference_size. +dnl +AC_DEFUN([GLIBCXX_CHECK_ALIGNAS_CACHELINE], [ + AC_LANG_SAVE + AC_LANG_CPLUSPLUS + + AC_MSG_CHECKING([whether static objects can be aligned to the cacheline size]) + AC_TRY_COMPILE(, [struct alignas(__GCC_DESTRUCTIVE_SIZE) Aligned { }; + alignas(Aligned) static char buf[sizeof(Aligned) * 16]; + ], [ac_alignas_cacheline=yes], [ac_alignas_cacheline=no]) + if test "$ac_alignas_cacheline" = yes; then + AC_DEFINE_UNQUOTED(_GLIBCXX_CAN_ALIGNAS_DESTRUCTIVE_SIZE, 1, + [Define if global objects can be aligned to + std::hardware_destructive_interference_size.]) + fi + AC_MSG_RESULT($ac_alignas_cacheline) + + AC_LANG_RESTORE +]) + # Macros from the top-level gcc directory. m4_include([../config/gc++filt.m4]) m4_include([../config/tls.m4]) diff --git a/libstdc++-v3/config.h.in b/libstdc++-v3/config.h.in index f91f7eb9097..bbb2613ff69 100644 --- a/libstdc++-v3/config.h.in +++ b/libstdc++-v3/config.h.in @@ -819,6 +819,10 @@ /* Define if the compiler supports C++11 atomics. */ #undef _GLIBCXX_ATOMIC_BUILTINS +/* Define if global objects can be aligned to + std::hardware_destructive_interference_size. */ +#undef _GLIBCXX_CAN_ALIGNAS_DESTRUCTIVE_SIZE + /* Define to use concept checking code from the boost libraries. */ #undef _GLIBCXX_CONCEPT_CHECKS diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure index a9589d882e6..188be08d716 100755 --- a/libstdc++-v3/configure +++ b/libstdc++-v3/configure @@ -71957,6 +71957,54 @@ _ACEOF fi + + + ac_ext=cpp +ac_cpp='$CXXCPP $CPPFLAGS' +ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5' +ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5' +ac_compiler_gnu=$ac_cv_cxx_compiler_gnu + + + { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether static objects can be aligned to the cacheline size" >&5 +$as_echo_n "checking whether static objects can be aligned to the cacheline size... " >&6; } + cat confdefs.h - <<_ACEOF >conftest.$ac_ext +/* end confdefs.h. */ + +int +main () +{ +struct alignas(__GCC_DESTRUCTIVE_SIZE) Aligned { }; + alignas(Aligned) static char buf[sizeof(Aligned) * 16]; + + ; + return 0; +} +_ACEOF +if ac_fn_cxx_try_compile "$LINENO"; then : + ac_alignas_cacheline=yes +else + ac_alignas_cacheline=no +fi +rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext + if test "$ac_alignas_cacheline" = yes; then + +cat >>confdefs.h <<_ACEOF +#define _GLIBCXX_CAN_ALIGNAS_DESTRUCTIVE_SIZE 1 +_ACEOF + + fi + { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_alignas_cacheline" >&5 +$as_echo "$ac_alignas_cacheline" >&6; } + + ac_ext=c +ac_cpp='$CPP $CPPFLAGS' +ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5' +ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5' +ac_compiler_gnu=$ac_cv_c_compiler_gnu + + + # Define documentation rules conditionally. # See if makeinfo has been installed and is modern enough diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac index 0dd550a4b4b..df01f58bd83 100644 --- a/libstdc++-v3/configure.ac +++ b/libstdc++-v3/configure.ac @@ -538,6 +538,9 @@ GLIBCXX_EMERGENCY_EH_ALLOC # For src/c++20/tzdb.cc defaults. GLIBCXX_ZONEINFO_DIR +# For src/c++11/shared_ptr.cc alignment. +GLIBCXX_CHECK_ALIGNAS_CACHELINE + # Define documentation rules conditionally. # See if makeinfo has been installed and is modern enough diff --git a/libstdc++-v3/src/c++11/shared_ptr.cc b/libstdc++-v3/src/c++11/shared_ptr.cc index 74e879e5828..ae47ca03301 100644 --- a/libstdc++-v3/src/c++11/shared_ptr.cc +++ b/libstdc++-v3/src/c++11/shared_ptr.cc @@ -34,8 +34,12 @@ namespace __gnu_internal _GLIBCXX_VISIBILITY(hidden) __gnu_cxx::__mutex& get_mutex(unsigned char i) { - // increase alignment to put each lock on a separate cache line - struct alignas(64) M : __gnu_cxx::__mutex { }; +#ifdef _GLIBCXX_CAN_ALIGNAS_DESTRUCTIVE_SIZE + // Increase alignment to put each lock on a separate cache line. + struct alignas(__GCC_DESTRUCTIVE_SIZE) M : __gnu_cxx::__mutex { }; +#else + using M = __gnu_cxx::__mutex; +#endif // Use a static buffer, so that the mutexes are not destructed // before potential users (or at all) static __attribute__ ((aligned(__alignof__(M)))) -- 2.40.1