diff options
author | Jonathan Wakely <jwakely@redhat.com> | 2023-05-16 15:09:20 +0100 |
---|---|---|
committer | Jonathan Wakely <jwakely@redhat.com> | 2023-05-16 18:31:19 +0100 |
commit | 94a311abf783de754f0f1b2d4c1f00a9788e795b (patch) | |
tree | 61e5fc53f07b21755c5edd434d205c8be5e39383 | |
parent | d5e5007c4b534391c0a97be56f6024fde1a88682 (diff) | |
download | gcc-94a311abf783de754f0f1b2d4c1f00a9788e795b.tar.gz |
libstdc++: Disable cacheline alignment for DJGPP [PR109741]
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.
-rw-r--r-- | libstdc++-v3/acinclude.m4 | 25 | ||||
-rw-r--r-- | libstdc++-v3/config.h.in | 4 | ||||
-rwxr-xr-x | libstdc++-v3/configure | 48 | ||||
-rw-r--r-- | libstdc++-v3/configure.ac | 3 | ||||
-rw-r--r-- | 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)))) |