On Tue, 8 Jul 2025 at 11:31, Björn Schäpers <g...@hazardy.de> wrote:
>
> Am 08.07.2025 um 12:01 schrieb Jonathan Wakely:
> > On Mon, 7 Jul 2025 at 23:53, Björn Schäpers <g...@hazardy.de> wrote:
> >>
> >> From: Björn Schäpers <bjo...@hazardy.de>
> >>
> >> Windows does not provide a tzdata.zi, but msys does. Use this, if
> >> available, instead of the embedded (and possibly outdated) database.
> >>
> >> libstdc++-v3/Changelog:
> >>
> >> Use msys provided time zone information.
> >>
> >> * src/c++20/tzdb.cc (zoneinfo_file): On Windows look relative
> >> from the DLL path for the time zone information.
> >>
> >> Signed-off-by: Björn Schäpers <bjo...@hazardy.de>
> >> ---
> >> libstdc++-v3/src/c++20/tzdb.cc | 34 ++++++++++++++++++++++++++++++++++
> >> 1 file changed, 34 insertions(+)
> >>
> >> diff --git a/libstdc++-v3/src/c++20/tzdb.cc
> >> b/libstdc++-v3/src/c++20/tzdb.cc
> >> index 6e244dc656d..9923d14b7a7 100644
> >> --- a/libstdc++-v3/src/c++20/tzdb.cc
> >> +++ b/libstdc++-v3/src/c++20/tzdb.cc
> >> @@ -44,6 +44,12 @@
> >> # include <cstdlib> // getenv
> >> #endif
> >>
> >> +#if _GLIBCXX_HAVE_WINDOWS_H
> >> +# define WIN32_LEAN_AND_MEAN
> >> +# include <windows.h>
> >> +# include <psapi.h>
> >> +#endif
> >> +
> >> #if defined __GTHREADS && ATOMIC_POINTER_LOCK_FREE == 2
> >> # define USE_ATOMIC_LIST_HEAD 1
> >> // TODO benchmark atomic<shared_ptr<>> vs mutex.
> >> @@ -1144,6 +1150,34 @@ namespace std::chrono
> >> #ifdef _GLIBCXX_ZONEINFO_DIR
> >> else
> >> path = _GLIBCXX_ZONEINFO_DIR;
> >> +#endif
> >> +#ifdef _GLIBCXX_HAVE_WINDOWS_H
> >> + if (path.empty())
> >> + {
> >> + HMODULE dll_module;
> >> + if (GetModuleHandleExA(
> >> + GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS
> >> + | GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT,
> >> + reinterpret_cast<const char *>(&zoneinfo_file),
> >> &dll_module))
> >
> > Does this assume that libstdc++.dll is installed as part of the msys
> > installation?
> >
> > What if users build GCC themselves and install it elsewhere?
> >
> > Is the correct solution for msys-based systems to build GCC with
> > --with-libstdcxx-zoneinfo=/path/to/msys/tzdata.zi ?
> >
>
> Yes the assumption is, that libstdc++-6.dll is installed in
> $msysPath/$msysSubsystem/bin and the time zones are in ../share/zoneinfo.
>
> If supplied with --with-libstdcxx-zoneinfo=/path/to/msys/tzdata.zi path
> shouldn't be empty, but containing "/path/to/msys/tzdata.zi" and nothing
> changes
> with my patch.
>
> The problem for msys packages is, that $msysPath is unknown, since the user
> can
> install msys anywhere. I tried using a long string constant and changing that
> in
> the DLL after installation, so it would remain a constant. But the string
> constant size is used to build the std::string and "/tzdata.zi" is appended to
> that. So I switched to use a runtime approach.
Makes sense. So the configure option might work, but if it doesn't,
the runtime approach might work (if libstdc++-6.dll and tzdata.zi have
the expected relative layout), and if not, we use the static copy of
tzdata.zi in the library.
Thanks, this still seems like a net improvement, even if it's not 100%
guaranteed to work.
>
> >
> >> + {
> >> + char dll_path[MAX_PATH];
> >> + if (GetModuleFileNameA(dll_module, dll_path, MAX_PATH) != 0)
> >> + {
> >> + string_view dll_path_view = dll_path;
> >> + auto pos = dll_path_view.find_last_of('\\');
> >> + dll_path_view = dll_path_view.substr(0, pos);
> >> + if (dll_path_view.ends_with("\\bin"))
> >> + {
> >> + constexpr string_view remaining_path =
> >> "share\\zoneinfo";
> >> + dll_path_view.remove_suffix(3); // Remove bin
> >> + path.reserve(dll_path_view.size()
> >> + + remaining_path.size());
> >> + path = dll_path_view;
> >> + path += remaining_path;
> >> + }
> >> + }
> >> + }
> >> + }
> >> #endif
> >> if (!path.empty())
> >> path.append(filename);
> >> --
> >> 2.50.0
> >>
> >
>
