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| 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 /libstdc++-v3/acinclude.m4 | |
| parent | d5e5007c4b534391c0a97be56f6024fde1a88682 (diff) | |
| download | gcc-94a311abf783de754f0f1b2d4c1f00a9788e795b.zip gcc-94a311abf783de754f0f1b2d4c1f00a9788e795b.tar.gz gcc-94a311abf783de754f0f1b2d4c1f00a9788e795b.tar.bz2 | |
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.
Diffstat (limited to 'libstdc++-v3/acinclude.m4')
| -rw-r--r-- | libstdc++-v3/acinclude.m4 | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4 index 988c532..8129373 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]) |