It's wrong to assume that clock_gettime is unavailable on any *-*-linux* target that doesn't have glibc 2.17 or later. Use a generic test instead of using __GLIBC_PREREQ. Only do that test when is_hosted=yes so that we don't get an error for cross targets without a working linker.
This ensures that C library's clock_gettime will be used on non-glibc targets, instead of an incorrect syscall to SYS_clock_gettime. PR libstdc++/93325 * acinclude.m4 (GLIBCXX_ENABLE_LIBSTDCXX_TIME): Use AC_SEARCH_LIBS for clock_gettime instead of explicit glibc version check. * configure: Regenerate. Tested powerpc64le-linux, built on centos7 and centos6 as well to check the results are correct for various versions of glibc. Committed to master. I plan to backport this later too.
commit 759812fddc81c0c131d4633b2a7f56412ce8dbed Author: Jonathan Wakely <jwak...@redhat.com> Date: Tue Jan 28 13:24:09 2020 +0000 libstdc++: Replace glibc-specific check for clock_gettime (PR 93325) It's wrong to assume that clock_gettime is unavailable on any *-*-linux* target that doesn't have glibc 2.17 or later. Use a generic test instead of using __GLIBC_PREREQ. Only do that test when is_hosted=yes so that we don't get an error for cross targets without a working linker. This ensures that C library's clock_gettime will be used on non-glibc targets, instead of an incorrect syscall to SYS_clock_gettime. PR libstdc++/93325 * acinclude.m4 (GLIBCXX_ENABLE_LIBSTDCXX_TIME): Use AC_SEARCH_LIBS for clock_gettime instead of explicit glibc version check. * configure: Regenerate. diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4 index 39147916e94..ee5e0336f2c 100644 --- a/libstdc++-v3/acinclude.m4 +++ b/libstdc++-v3/acinclude.m4 @@ -1422,20 +1422,14 @@ AC_DEFUN([GLIBCXX_ENABLE_LIBSTDCXX_TIME], [ ac_has_nanosleep=yes ;; gnu* | linux* | kfreebsd*-gnu | knetbsd*-gnu) - AC_MSG_CHECKING([for at least GNU libc 2.17]) - AC_TRY_COMPILE( - [#include <features.h>], - [ - #if ! __GLIBC_PREREQ(2, 17) - #error - #endif - ], - [glibcxx_glibc217=yes], [glibcxx_glibc217=no]) - AC_MSG_RESULT($glibcxx_glibc217) - - if test x"$glibcxx_glibc217" = x"yes"; then - ac_has_clock_monotonic=yes - ac_has_clock_realtime=yes + # Don't use link test for freestanding library, in case gcc_no_link=yes + if test x"$is_hosted" = xyes; then + # Versions of glibc before 2.17 needed -lrt for clock_gettime. + AC_SEARCH_LIBS(clock_gettime, [rt]) + if test x"$ac_cv_search_clock_gettime" = x"none required"; then + ac_has_clock_monotonic=yes + ac_has_clock_realtime=yes + fi fi ac_has_nanosleep=yes ac_has_sched_yield=yes