On Wed, 2 Apr 2025 at 07:16, Tomasz Kaminski <tkami...@redhat.com> wrote:
>
>
>
> On Tue, Apr 1, 2025 at 2:46 PM Jonathan Wakely <jwak...@redhat.com> wrote:
>>
>> On Tue, 1 Apr 2025 at 11:34, Tomasz Kaminski <tkami...@redhat.com> wrote:
>> >
>> >
>> >
>> > On Mon, Mar 31, 2025 at 7:28 PM Jonathan Wakely <jwak...@redhat.com> wrote:
>> >>
>> >> In r15-8491-g778c28c70f8573 I added a use of the Autoconf macro
>> >> AC_STRUCT_TIMEZONE, but that requires a link-test for the global tzname
>> >> object if tm.tm_zone isn't supported. That link-test isn't allowed for
>> >> cross-compilation, so bootstrap fails if tm.tm_zone isn't supported.
>> >>
>> >> Since libstdc++ only cares about tm.tm_zone and won't use tzname anyway,
>> >> we don't need the link-test. Replace AC_STRUCT_TIMEZONE with a custom
>> >> macro that only checks for tm.tm_zone. We can improve on the Autoconf
>> >> macro by checking it's a suitable type, which isn't actually checked by
>> >> AC_STRUCT_TIMEZONE.
>> >>
>> >> libstdc++-v3/ChangeLog:
>> >>
>> >> PR libstdc++/119550
>> >> * acinclude.m4 (GLIBCXX_STRUCT_TM_TM_ZONE): New macro.
>> >> * config.h.in: Regenerate.
>> >> * configure: Regenerate.
>> >> * configure.ac: Use GLIBCXX_STRUCT_TM_TM_ZONE.
>> >> * include/bits/chrono_io.h (__formatter_chrono::_M_c): Check
>> >> _GLIBCXX_USE_STRUCT_TM_TM_ZONE instead of
>> >> _GLIBCXX_HAVE_STRUCT_TM_TM_ZONE.
>> >> ---
>> >>
>> >> Testing x86_64-linux and sparc-solaris2.11, looks fine so far.
>> >>
>> >> libstdc++-v3/acinclude.m4 | 35 ++++
>> >> libstdc++-v3/config.h.in | 21 +--
>> >> libstdc++-v3/configure | 238 ++++++++------------------
>> >> libstdc++-v3/configure.ac | 5 +-
>> >> libstdc++-v3/include/bits/chrono_io.h | 2 +-
>> >> 5 files changed, 109 insertions(+), 192 deletions(-)
>> >>
>> >> diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
>> >> index e668d2dba27..02fd349e11d 100644
>> >> --- a/libstdc++-v3/acinclude.m4
>> >> +++ b/libstdc++-v3/acinclude.m4
>> >> @@ -5744,6 +5744,41 @@ AC_DEFUN([GLIBCXX_ZONEINFO_DIR], [
>> >> fi
>> >> ])
>> >>
>> >> +dnl
>> >> +dnl Check for a tm_zone member in struct tm.
>> >> +dnl
>> >> +dnl This member is defined as const char* in Glibc, newlib, POSIX.1-2024,
>> >> +dnl and as char* in BSD (including macOS).
>> >> +dnl
>> >> +dnl Defines:
>> >> +dnl _GLIBCXX_USE_STRUCT_TM_TM_ZONE if struct tm has a tm_zone member.
>> >> +dnl
>> >> +AC_DEFUN([GLIBCXX_STRUCT_TM_TM_ZONE], [
>> >> +
>> >> + AC_LANG_SAVE
>> >
>> > From documentation this is deprecated in favor of AC_LANG_PUSH.
>>
>> It looks like that is supported by autoconf 2.69 and is already used
>> elsewhere in GCC. We don't currently use it in libstdc++ but it should
>> be safe to do so.
>>
>> >> + AC_LANG_CPLUSPLUS
>> >> + ac_save_CXXFLAGS="$CXXFLAGS"
>> >> + CXXFLAGS="$CXXFLAGS -std=c++20"
>> >
>> > The program that is compiled does not seem to require C++20.
>> > If we change the declaration of "t" to use "= {}", we could do it in C++98.
>> > Any reason to adjust the flags at all?
>>
>> We only need to use the tm_zone member in C++20 mode, and it's
>> possible that on some platform it's not exposed for older standards
>> (very unlikely, but possible). I wanted to test for exactly what we
>> require. I don't feel strongly about it though.
>
> I would found it surprising if the layout of the structure would fiffer that
> much,
> wouldn't this cause ABI compatibility problems for TU that memcopies struct tm
> and are compiled with different language versions?
Not if it does:
#if _USE_POSIX24
const char* tm_zone;
#else
const void* __tm_zone_padding;
#endif
> I have slight preference towards not overriding CXXFLAGS, as for me this
> suggest
> that struct tm was changed in C++20 (or linked C standard), which is not the
> case.
> But I am fine either way.
IMHO the test should be understood as "can C++20 chrono formatting use
tm_zone", and not "is tm_zone defined in C++20", which is partly why I
defined a USE macro nto a HAVE macro (but also to avoid conflicting
with the name that AC_STRUCT_TIMEZONE uses). I should have said that
in the comments above the GLIBCXX_STRUCT_TM_TM_ZONE definition though!
I'll improve that (and revisit the AC_PUSH_LANG point in stage 1).
>>
>>
>> >>
>> >> +
>> >> + AC_CACHE_CHECK([for tm_zone member of struct tm], glibcxx_cv_tm_zone, [
>> >> + AC_COMPILE_IFELSE([AC_LANG_PROGRAM([#include <time.h>
>> >> + ],
>> >> + [struct tm t{}; t.tm_zone = (char*)0;]
>> >> + )],
>> >> + [glibcxx_cv_tm_zone=yes],
>> >> + [glibcxx_cv_tm_zone=no]
>> >> + )
>> >> + ])
>> >> +
>> >> + if test $glibcxx_cv_tm_zone = yes; then
>> >> + AC_DEFINE(_GLIBCXX_USE_STRUCT_TM_TM_ZONE, 1,
>> >> + [Define if struct tm has a tm_zone member.])
>> >> + fi
>> >> +
>> >> + CXXFLAGS="$ac_save_CXXFLAGS"
>> >> + AC_LANG_RESTORE
>> >> +])
>> >> +
>> >> dnl
>> >> dnl Check whether lock tables can be aligned to avoid false sharing.
>> >> dnl
>> >> diff --git a/libstdc++-v3/config.h.in b/libstdc++-v3/config.h.in
>> >> index be151f43dd6..77bbaf1beaa 100644
>> >> --- a/libstdc++-v3/config.h.in
>> >> +++ b/libstdc++-v3/config.h.in
>> >> @@ -74,10 +74,6 @@
>> >> don't. */
>> >> #undef HAVE_DECL_STRNLEN
>> >>
>> >> -/* Define to 1 if you have the declaration of `tzname', and to 0 if you
>> >> don't.
>> >> - */
>> >> -#undef HAVE_DECL_TZNAME
>> >> -
>> >> /* Define to 1 if you have the <dirent.h> header file. */
>> >> #undef HAVE_DIRENT_H
>> >>
>> >> @@ -412,9 +408,6 @@
>> >> /* Define to 1 if `d_type' is a member of `struct dirent'. */
>> >> #undef HAVE_STRUCT_DIRENT_D_TYPE
>> >>
>> >> -/* Define to 1 if `tm_zone' is a member of `struct tm'. */
>> >> -#undef HAVE_STRUCT_TM_TM_ZONE
>> >> -
>> >> /* Define if strxfrm_l is available in <string.h>. */
>> >> #undef HAVE_STRXFRM_L
>> >>
>> >> @@ -506,17 +499,9 @@
>> >> /* Define to 1 if the target supports thread-local storage. */
>> >> #undef HAVE_TLS
>> >>
>> >> -/* Define to 1 if your `struct tm' has `tm_zone'. Deprecated, use
>> >> - `HAVE_STRUCT_TM_TM_ZONE' instead. */
>> >> -#undef HAVE_TM_ZONE
>> >> -
>> >> /* Define if truncate is available in <unistd.h>. */
>> >> #undef HAVE_TRUNCATE
>> >>
>> >> -/* Define to 1 if you don't have `tm_zone' but do have the external array
>> >> - `tzname'. */
>> >> -#undef HAVE_TZNAME
>> >> -
>> >> /* Define to 1 if you have the <uchar.h> header file. */
>> >> #undef HAVE_UCHAR_H
>> >>
>> >> @@ -605,9 +590,6 @@
>> >> /* Define to 1 if you have the ANSI C header files. */
>> >> #undef STDC_HEADERS
>> >>
>> >> -/* Define to 1 if your <sys/time.h> declares `struct tm'. */
>> >> -#undef TM_IN_SYS_TIME
>> >> -
>> >> /* Version number of package */
>> >> #undef VERSION
>> >>
>> >> @@ -906,6 +888,9 @@
>> >> /* Define to restrict std::__basic_file<> to stdio APIs. */
>> >> #undef _GLIBCXX_USE_STDIO_PURE
>> >>
>> >> +/* Define if struct tm has a tm_zone member. */
>> >> +#undef _GLIBCXX_USE_STRUCT_TM_TM_ZONE
>> >> +
>> >> /* Define if struct stat has timespec members. */
>> >> #undef _GLIBCXX_USE_ST_MTIM
>> >>
>> >> diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
>> >> index 67d2b8c7b72..56d0bcb297e 100755
>> >> --- a/libstdc++-v3/configure
>> >> +++ b/libstdc++-v3/configure
>> >> @@ -2731,63 +2731,6 @@ $as_echo "$ac_res" >&6; }
>> >> eval $as_lineno_stack; ${as_lineno_stack:+:} unset as_lineno
>> >>
>> >> } # ac_fn_c_check_decl
>> >> -
>> >> -# ac_fn_c_check_member LINENO AGGR MEMBER VAR INCLUDES
>> >> -# ----------------------------------------------------
>> >> -# Tries to find if the field MEMBER exists in type AGGR, after including
>> >> -# INCLUDES, setting cache variable VAR accordingly.
>> >> -ac_fn_c_check_member ()
>> >> -{
>> >> - as_lineno=${as_lineno-"$1"}
>> >> as_lineno_stack=as_lineno_stack=$as_lineno_stack
>> >> - { $as_echo "$as_me:${as_lineno-$LINENO}: checking for $2.$3" >&5
>> >> -$as_echo_n "checking for $2.$3... " >&6; }
>> >> -if eval \${$4+:} false; then :
>> >> - $as_echo_n "(cached) " >&6
>> >> -else
>> >> - cat confdefs.h - <<_ACEOF >conftest.$ac_ext
>> >> -/* end confdefs.h. */
>> >> -$5
>> >> -int
>> >> -main ()
>> >> -{
>> >> -static $2 ac_aggr;
>> >> -if (ac_aggr.$3)
>> >> -return 0;
>> >> - ;
>> >> - return 0;
>> >> -}
>> >> -_ACEOF
>> >> -if ac_fn_c_try_compile "$LINENO"; then :
>> >> - eval "$4=yes"
>> >> -else
>> >> - cat confdefs.h - <<_ACEOF >conftest.$ac_ext
>> >> -/* end confdefs.h. */
>> >> -$5
>> >> -int
>> >> -main ()
>> >> -{
>> >> -static $2 ac_aggr;
>> >> -if (sizeof ac_aggr.$3)
>> >> -return 0;
>> >> - ;
>> >> - return 0;
>> >> -}
>> >> -_ACEOF
>> >> -if ac_fn_c_try_compile "$LINENO"; then :
>> >> - eval "$4=yes"
>> >> -else
>> >> - eval "$4=no"
>> >> -fi
>> >> -rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
>> >> -fi
>> >> -rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
>> >> -fi
>> >> -eval ac_res=\$$4
>> >> - { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_res"
>> >> >&5
>> >> -$as_echo "$ac_res" >&6; }
>> >> - eval $as_lineno_stack; ${as_lineno_stack:+:} unset as_lineno
>> >> -
>> >> -} # ac_fn_c_check_member
>> >> cat >config.log <<_ACEOF
>> >> This file contains any messages produced by compilers while
>> >> running configure, to aid debugging if configure makes a mistake.
>> >> @@ -12337,7 +12280,7 @@ else
>> >> lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
>> >> lt_status=$lt_dlunknown
>> >> cat > conftest.$ac_ext <<_LT_EOF
>> >> -#line 12340 "configure"
>> >> +#line 12283 "configure"
>> >> #include "confdefs.h"
>> >>
>> >> #if HAVE_DLFCN_H
>> >> @@ -12443,7 +12386,7 @@ else
>> >> lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
>> >> lt_status=$lt_dlunknown
>> >> cat > conftest.$ac_ext <<_LT_EOF
>> >> -#line 12446 "configure"
>> >> +#line 12389 "configure"
>> >> #include "confdefs.h"
>> >>
>> >> #if HAVE_DLFCN_H
>> >> @@ -16239,7 +16182,7 @@ $as_echo "$glibcxx_cv_atomic_long_long" >&6; }
>> >> # Fake what AC_TRY_COMPILE does.
>> >>
>> >> cat > conftest.$ac_ext << EOF
>> >> -#line 16242 "configure"
>> >> +#line 16185 "configure"
>> >> int main()
>> >> {
>> >> typedef bool atomic_type;
>> >> @@ -16274,7 +16217,7 @@ $as_echo "$glibcxx_cv_atomic_bool" >&6; }
>> >> rm -f conftest*
>> >>
>> >> cat > conftest.$ac_ext << EOF
>> >> -#line 16277 "configure"
>> >> +#line 16220 "configure"
>> >> int main()
>> >> {
>> >> typedef short atomic_type;
>> >> @@ -16309,7 +16252,7 @@ $as_echo "$glibcxx_cv_atomic_short" >&6; }
>> >> rm -f conftest*
>> >>
>> >> cat > conftest.$ac_ext << EOF
>> >> -#line 16312 "configure"
>> >> +#line 16255 "configure"
>> >> int main()
>> >> {
>> >> // NB: _Atomic_word not necessarily int.
>> >> @@ -16345,7 +16288,7 @@ $as_echo "$glibcxx_cv_atomic_int" >&6; }
>> >> rm -f conftest*
>> >>
>> >> cat > conftest.$ac_ext << EOF
>> >> -#line 16348 "configure"
>> >> +#line 16291 "configure"
>> >> int main()
>> >> {
>> >> typedef long long atomic_type;
>> >> @@ -16501,7 +16444,7 @@ $as_echo "mutex" >&6; }
>> >> # unnecessary for this test.
>> >>
>> >> cat > conftest.$ac_ext << EOF
>> >> -#line 16504 "configure"
>> >> +#line 16447 "configure"
>> >> int main()
>> >> {
>> >> _Decimal32 d1;
>> >> @@ -16543,7 +16486,7 @@ ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
>> >> # unnecessary for this test.
>> >>
>> >> cat > conftest.$ac_ext << EOF
>> >> -#line 16546 "configure"
>> >> +#line 16489 "configure"
>> >> template<typename T1, typename T2>
>> >> struct same
>> >> { typedef T2 type; };
>> >> @@ -54482,6 +54425,65 @@ _ACEOF
>> >> fi
>> >>
>> >>
>> >> +# For std::chrono formatters to use tm::tm_zone
>> >> +
>> >> +
>> >> +
>> >> + 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
>> >> +
>> >> + ac_save_CXXFLAGS="$CXXFLAGS"
>> >> + CXXFLAGS="$CXXFLAGS -std=c++20"
>> >> +
>> >> + { $as_echo "$as_me:${as_lineno-$LINENO}: checking for tm_zone member
>> >> of struct tm" >&5
>> >> +$as_echo_n "checking for tm_zone member of struct tm... " >&6; }
>> >> +if ${glibcxx_cv_tm_zone+:} false; then :
>> >> + $as_echo_n "(cached) " >&6
>> >> +else
>> >> +
>> >> + cat confdefs.h - <<_ACEOF >conftest.$ac_ext
>> >> +/* end confdefs.h. */
>> >> +#include <time.h>
>> >> +
>> >> +int
>> >> +main ()
>> >> +{
>> >> +struct tm t{}; t.tm_zone = (char*)0;
>> >> +
>> >> + ;
>> >> + return 0;
>> >> +}
>> >> +_ACEOF
>> >> +if ac_fn_cxx_try_compile "$LINENO"; then :
>> >> + glibcxx_cv_tm_zone=yes
>> >> +else
>> >> + glibcxx_cv_tm_zone=no
>> >> +
>> >> +fi
>> >> +rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
>> >> +
>> >> +fi
>> >> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $glibcxx_cv_tm_zone" >&5
>> >> +$as_echo "$glibcxx_cv_tm_zone" >&6; }
>> >> +
>> >> + if test $glibcxx_cv_tm_zone = yes; then
>> >> +
>> >> +$as_echo "#define _GLIBCXX_USE_STRUCT_TM_TM_ZONE 1" >>confdefs.h
>> >> +
>> >> + fi
>> >> +
>> >> + CXXFLAGS="$ac_save_CXXFLAGS"
>> >> + ac_ext=c
>> >> +ac_cpp='$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
>> >> +
>> >> +
>> >> +
>> >> # For src/c++11/shared_ptr.cc alignment.
>> >>
>> >>
>> >> @@ -54697,112 +54699,6 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
>> >>
>> >>
>> >>
>> >> -{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether struct tm is
>> >> in sys/time.h or time.h" >&5
>> >> -$as_echo_n "checking whether struct tm is in sys/time.h or time.h... "
>> >> >&6; }
>> >> -if ${ac_cv_struct_tm+:} false; then :
>> >> - $as_echo_n "(cached) " >&6
>> >> -else
>> >> - cat confdefs.h - <<_ACEOF >conftest.$ac_ext
>> >> -/* end confdefs.h. */
>> >> -#include <sys/types.h>
>> >> -#include <time.h>
>> >> -
>> >> -int
>> >> -main ()
>> >> -{
>> >> -struct tm tm;
>> >> - int *p = &tm.tm_sec;
>> >> - return !p;
>> >> - ;
>> >> - return 0;
>> >> -}
>> >> -_ACEOF
>> >> -if ac_fn_c_try_compile "$LINENO"; then :
>> >> - ac_cv_struct_tm=time.h
>> >> -else
>> >> - ac_cv_struct_tm=sys/time.h
>> >> -fi
>> >> -rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
>> >> -fi
>> >> -{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_struct_tm" >&5
>> >> -$as_echo "$ac_cv_struct_tm" >&6; }
>> >> -if test $ac_cv_struct_tm = sys/time.h; then
>> >> -
>> >> -$as_echo "#define TM_IN_SYS_TIME 1" >>confdefs.h
>> >> -
>> >> -fi
>> >> -
>> >> -ac_fn_c_check_member "$LINENO" "struct tm" "tm_zone"
>> >> "ac_cv_member_struct_tm_tm_zone" "#include <sys/types.h>
>> >> -#include <$ac_cv_struct_tm>
>> >> -
>> >> -"
>> >> -if test "x$ac_cv_member_struct_tm_tm_zone" = xyes; then :
>> >> -
>> >> -cat >>confdefs.h <<_ACEOF
>> >> -#define HAVE_STRUCT_TM_TM_ZONE 1
>> >> -_ACEOF
>> >> -
>> >> -
>> >> -fi
>> >> -
>> >> -if test "$ac_cv_member_struct_tm_tm_zone" = yes; then
>> >> -
>> >> -$as_echo "#define HAVE_TM_ZONE 1" >>confdefs.h
>> >> -
>> >> -else
>> >> - ac_fn_c_check_decl "$LINENO" "tzname" "ac_cv_have_decl_tzname"
>> >> "#include <time.h>
>> >> -"
>> >> -if test "x$ac_cv_have_decl_tzname" = xyes; then :
>> >> - ac_have_decl=1
>> >> -else
>> >> - ac_have_decl=0
>> >> -fi
>> >> -
>> >> -cat >>confdefs.h <<_ACEOF
>> >> -#define HAVE_DECL_TZNAME $ac_have_decl
>> >> -_ACEOF
>> >> -
>> >> - { $as_echo "$as_me:${as_lineno-$LINENO}: checking for tzname" >&5
>> >> -$as_echo_n "checking for tzname... " >&6; }
>> >> -if ${ac_cv_var_tzname+:} false; then :
>> >> - $as_echo_n "(cached) " >&6
>> >> -else
>> >> - if test x$gcc_no_link = xyes; then
>> >> - as_fn_error $? "Link tests are not allowed after GCC_NO_EXECUTABLES."
>> >> "$LINENO" 5
>> >> -fi
>> >> -cat confdefs.h - <<_ACEOF >conftest.$ac_ext
>> >> -/* end confdefs.h. */
>> >> -#include <time.h>
>> >> -#if !HAVE_DECL_TZNAME
>> >> -extern char *tzname[];
>> >> -#endif
>> >> -
>> >> -int
>> >> -main ()
>> >> -{
>> >> -return tzname[0][0];
>> >> - ;
>> >> - return 0;
>> >> -}
>> >> -_ACEOF
>> >> -if ac_fn_c_try_link "$LINENO"; then :
>> >> - ac_cv_var_tzname=yes
>> >> -else
>> >> - ac_cv_var_tzname=no
>> >> -fi
>> >> -rm -f core conftest.err conftest.$ac_objext \
>> >> - conftest$ac_exeext conftest.$ac_ext
>> >> -fi
>> >> -{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_var_tzname" >&5
>> >> -$as_echo "$ac_cv_var_tzname" >&6; }
>> >> - if test $ac_cv_var_tzname = yes; then
>> >> -
>> >> -$as_echo "#define HAVE_TZNAME 1" >>confdefs.h
>> >> -
>> >> - fi
>> >> -fi
>> >> -
>> >> -
>> >> # 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 fe0cdde1f7a..a6c01b29e94 100644
>> >> --- a/libstdc++-v3/configure.ac
>> >> +++ b/libstdc++-v3/configure.ac
>> >> @@ -572,6 +572,9 @@ GLIBCXX_EMERGENCY_EH_ALLOC
>> >> # For src/c++20/tzdb.cc defaults.
>> >> GLIBCXX_ZONEINFO_DIR
>> >>
>> >> +# For std::chrono formatters to use tm::tm_zone
>> >> +GLIBCXX_STRUCT_TM_TM_ZONE
>> >> +
>> >> # For src/c++11/shared_ptr.cc alignment.
>> >> GLIBCXX_CHECK_ALIGNAS_CACHELINE
>> >>
>> >> @@ -584,8 +587,6 @@ GLIBCXX_CHECK_FILEBUF_NATIVE_HANDLES
>> >> # For std::text_encoding
>> >> GLIBCXX_CHECK_TEXT_ENCODING
>> >>
>> >> -AC_STRUCT_TIMEZONE
>> >> -
>> >> # Define documentation rules conditionally.
>> >>
>> >> # See if makeinfo has been installed and is modern enough
>> >> diff --git a/libstdc++-v3/include/bits/chrono_io.h
>> >> b/libstdc++-v3/include/bits/chrono_io.h
>> >> index 3a5bc5695fb..d8721093706 100644
>> >> --- a/libstdc++-v3/include/bits/chrono_io.h
>> >> +++ b/libstdc++-v3/include/bits/chrono_io.h
>> >> @@ -905,7 +905,7 @@ namespace __format
>> >> // time zone info available for the time in __tm.
>> >> __tm.tm_isdst = -1;
>> >>
>> >> -#ifdef _GLIBCXX_HAVE_STRUCT_TM_TM_ZONE
>> >> +#ifdef _GLIBCXX_USE_STRUCT_TM_TM_ZONE
>> >> // POSIX.1-2024 adds tm.tm_zone which will be used for %Z.
>> >> // BSD has had tm_zone since 1987 but as char* so cast away
>> >> const.
>> >> if constexpr (__is_time_point_v<_Tp>)
>> >> --
>> >> 2.49.0
>> >>
>>
