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.
>>
>> +
>> + 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
>>
