[PATCHv4] libstdc++: Move tai_- and gps_clock::now impls out of ABI
Jonathan Wakely
jwakely@redhat.com
Wed Aug 27 08:24:43 GMT 2025
On Tue, 26 Aug 2025 at 18:31, Nathan Myers <ncm@cantrip.org> wrote:
>
> Changes in v4:
> * Move global symbols to correct list.
> * Fix up commit annotations: Changelog, title.
>
> Changes in v3:
> * Add to global symbols list.
>
> Changes in v2:
> * tai_clock and gps_clock remain "is_steady = false".
> * Note adjustments to the exported global symbols list are
> not yet included in this patch.
>
> This patch moves std::tai_clock::now() and std::tai_clock::now()
> definitions from header inlines to static members invoked via a
> normal function call, in service of stabilizing the C++20 ABI.
>
> It also changes #if guards to mention the actual __cpp_lib_*
> feature gated, not just the language version, for clarity.
>
> New global function symbols std::chrono::tai_clock::now
> and std::chrono::gps_clock::now are exported.
OK for trunk, thanks
>
> libstdc++-v3/ChangeLog:
> * include/std/chrono (gps_clock::now, tai_clock::now): Remove
> inline definitions.
> * src/c++20/clock.cc (gps_clock::now, tai_clock::now): New file
> for out-of-line now() impls.
> * src/c++20/Makefile.am: Mention clock.cc.
> * src/c++20/Makefile.in: Regenerate.
> * config/abi/pre/gnu.ver: add mangled now() symbols.
> ---
> libstdc++-v3/config/abi/pre/gnu.ver | 4 +++
> libstdc++-v3/include/std/chrono | 32 +++++++++---------
> libstdc++-v3/src/c++20/Makefile.am | 2 +-
> libstdc++-v3/src/c++20/Makefile.in | 4 +--
> libstdc++-v3/src/c++20/clock.cc | 52 +++++++++++++++++++++++++++++
> 5 files changed, 74 insertions(+), 20 deletions(-)
> create mode 100644 libstdc++-v3/src/c++20/clock.cc
>
> diff --git a/libstdc++-v3/config/abi/pre/gnu.ver b/libstdc++-v3/config/abi/pre/gnu.ver
> index b5a89c31e0e..e1601dc39d2 100644
> --- a/libstdc++-v3/config/abi/pre/gnu.ver
> +++ b/libstdc++-v3/config/abi/pre/gnu.ver
> @@ -2555,6 +2555,10 @@ GLIBCXX_3.4.35 {
> _ZNSt8__detail17__wait_until_implEPKvRNS_16__wait_args_baseERKNSt6chrono8durationI[lx]St5ratioIL[lx]1EL[lx]1000000000EEEE;
> _ZNSt8__detail11__wait_args22_M_load_proxy_wait_valEPKv;
>
> + # std::chrono::gps_clock::now, tai_clock::now
> + _ZNSt6chrono9gps_clock3nowEv;
> + _ZNSt6chrono9tai_clock3nowEv;
> +
> # __gnu_debug::_Safe_iterator_base and _Safe_sequence_base const
> _ZN11__gnu_debug19_Safe_iterator_base9_M_attachEPKNS_19_Safe_sequence_baseEb;
> _ZN11__gnu_debug19_Safe_iterator_base16_M_attach_singleEPKNS_19_Safe_sequence_baseEb;
> diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono
> index cb8213e2f9f..d1a01fbdf0a 100644
> --- a/libstdc++-v3/include/std/chrono
> +++ b/libstdc++-v3/include/std/chrono
> @@ -22,6 +22,8 @@
> // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
> // <http://www.gnu.org/licenses/>.
>
> +// [time]
> +
> /** @file include/chrono
> * This is a Standard C++ Library header.
> * @ingroup chrono
> @@ -42,12 +44,16 @@
> # include <bits/c++0x_warning.h>
> #else
>
> +#define __glibcxx_want_chrono
> +#define __glibcxx_want_chrono_udls
> +#include <bits/version.h>
> +
> #include <bits/chrono.h>
>
> -#if __cplusplus >= 202002L
> +#if __cpp_lib_bitops >= 201907L
> # include <bit> // __countr_zero
> #endif
> -#if __cplusplus >= 202002L && _GLIBCXX_HOSTED
> +#if __cpp_lib_chrono >= 201803L && _GLIBCXX_HOSTED
> # include <sstream>
> # include <string>
> # include <vector>
> @@ -56,10 +62,6 @@
> # include <bits/unique_ptr.h>
> #endif
>
> -#define __glibcxx_want_chrono
> -#define __glibcxx_want_chrono_udls
> -#include <bits/version.h>
> -
> namespace std _GLIBCXX_VISIBILITY(default)
> {
> _GLIBCXX_BEGIN_NAMESPACE_VERSION
> @@ -79,7 +81,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> */
> namespace chrono
> {
> -#if __cplusplus >= 202002L
> +#if __cpp_lib_chrono >= 201803L
> /// @addtogroup chrono
> /// @{
> struct local_t { };
> @@ -175,13 +177,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> using period = system_clock::period;
> using duration = chrono::duration<rep, period>;
> using time_point = chrono::time_point<tai_clock>;
> - static constexpr bool is_steady = false; // XXX true for CLOCK_TAI?
> + static constexpr bool is_steady = false;
>
> - // TODO move into lib, use CLOCK_TAI on linux, add extension point.
> [[nodiscard]]
> static time_point
> - now()
> - { return from_utc(utc_clock::now()); }
> + now(); // in src/c++20/clock.cc
>
> template<typename _Duration>
> [[nodiscard]]
> @@ -215,13 +215,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> using period = system_clock::period;
> using duration = chrono::duration<rep, period>;
> using time_point = chrono::time_point<gps_clock>;
> - static constexpr bool is_steady = false; // XXX
> + static constexpr bool is_steady = false;
>
> - // TODO move into lib, add extension point.
> [[nodiscard]]
> static time_point
> - now()
> - { return from_utc(utc_clock::now()); }
> + now(); // in src/c++20/clock.cc
>
> template<typename _Duration>
> [[nodiscard]]
> @@ -3321,7 +3319,7 @@ namespace __detail
> #endif // C++20
> } // namespace chrono
>
> -#if __cplusplus >= 202002L
> +#if __cpp_lib_chrono >= 201803L
> inline namespace literals
> {
> inline namespace chrono_literals
> @@ -3350,7 +3348,7 @@ namespace __detail
> _GLIBCXX_END_NAMESPACE_VERSION
> } // namespace std
>
> -#if __cplusplus >= 202002L && _GLIBCXX_HOSTED
> +#if __cpp_lib_chrono >= 201803L && _GLIBCXX_HOSTED
> # include <bits/chrono_io.h>
> #endif
>
> diff --git a/libstdc++-v3/src/c++20/Makefile.am b/libstdc++-v3/src/c++20/Makefile.am
> index 15e6f3445fb..736558ff24a 100644
> --- a/libstdc++-v3/src/c++20/Makefile.am
> +++ b/libstdc++-v3/src/c++20/Makefile.am
> @@ -36,7 +36,7 @@ else
> inst_sources =
> endif
>
> -sources = tzdb.cc format.cc atomic.cc
> +sources = tzdb.cc format.cc atomic.cc clock.cc
>
> vpath % $(top_srcdir)/src/c++20
>
> diff --git a/libstdc++-v3/src/c++20/Makefile.in b/libstdc++-v3/src/c++20/Makefile.in
> index d9e1615bbca..3cb6d6fea5f 100644
> --- a/libstdc++-v3/src/c++20/Makefile.in
> +++ b/libstdc++-v3/src/c++20/Makefile.in
> @@ -121,7 +121,7 @@ CONFIG_CLEAN_FILES =
> CONFIG_CLEAN_VPATH_FILES =
> LTLIBRARIES = $(noinst_LTLIBRARIES)
> libc__20convenience_la_LIBADD =
> -am__objects_1 = tzdb.lo format.lo atomic.lo
> +am__objects_1 = tzdb.lo format.lo atomic.lo clock.lo
> @ENABLE_EXTERN_TEMPLATE_TRUE@am__objects_2 = sstream-inst.lo
> @GLIBCXX_HOSTED_TRUE@am_libc__20convenience_la_OBJECTS = \
> @GLIBCXX_HOSTED_TRUE@ $(am__objects_1) $(am__objects_2)
> @@ -432,7 +432,7 @@ headers =
> @ENABLE_EXTERN_TEMPLATE_TRUE@inst_sources = \
> @ENABLE_EXTERN_TEMPLATE_TRUE@ sstream-inst.cc
>
> -sources = tzdb.cc format.cc atomic.cc
> +sources = tzdb.cc format.cc atomic.cc clock.cc
> @GLIBCXX_HOSTED_FALSE@libc__20convenience_la_SOURCES =
> @GLIBCXX_HOSTED_TRUE@libc__20convenience_la_SOURCES = $(sources) $(inst_sources)
>
> diff --git a/libstdc++-v3/src/c++20/clock.cc b/libstdc++-v3/src/c++20/clock.cc
> new file mode 100644
> index 00000000000..2410f1a8fe5
> --- /dev/null
> +++ b/libstdc++-v3/src/c++20/clock.cc
> @@ -0,0 +1,52 @@
> +// std::chrono::tai_clock, gps_clock
> +
> +// Copyright (C) 2021-2025 Free Software Foundation, Inc.
> +//
> +// This file is part of the GNU ISO C++ Library. This library is free
> +// software; you can redistribute it and/or modify it under the
> +// terms of the GNU General Public License as published by the
> +// Free Software Foundation; either version 3, or (at your option)
> +// any later version.
> +
> +// This library is distributed in the hope that it will be useful,
> +// but WITHOUT ANY WARRANTY; without even the implied warranty of
> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +// GNU General Public License for more details.
> +
> +// Under Section 7 of GPL version 3, you are granted additional
> +// permissions described in the GCC Runtime Library Exception, version
> +// 3.1, as published by the Free Software Foundation.
> +
> +// You should have received a copy of the GNU General Public License and
> +// a copy of the GCC Runtime Library Exception along with this program;
> +// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
> +// <http://www.gnu.org/licenses/>.
> +
> +//
> +// ISO C++ 14882:2020
> +// 27.7.4 [time.clock.tai], 27.7.5 [time.clock.gps]
> +// P0355R7
> +
> +#include <chrono>
> +
> +namespace std _GLIBCXX_VISIBILITY(default)
> +{
> +_GLIBCXX_BEGIN_NAMESPACE_VERSION
> +
> +namespace chrono
> +{
> +#if __cpp_lib_chrono >= 201803L && _GLIBCXX_HOSTED
> + // TODO use CLOCK_TAI on linux, add extension point.
> + time_point<tai_clock>
> + tai_clock::now()
> + { return from_utc(utc_clock::now()); }
> +
> + // TODO add extension point.
> + time_point<gps_clock>
> + gps_clock::now()
> + { return from_utc(utc_clock::now()); }
> +#endif
> +}
> +
> +_GLIBCXX_END_NAMESPACE_VERSION
> +}
> --
> 2.50.1
>
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