[PATCH] libstdc++: Search for tzdata on Windows (msys)

[Björn Schäpers]

Am 07.07.2025 um 23:02 schrieb Jonathan Wakely:
> On Mon, 7 Jul 2025 at 22:01, Jonathan Wakely <jwakely@redhat.com> wrote:
>>
>> On Mon, 7 Jul 2025 at 21:26, Björn Schäpers <gcc@hazardy.de> wrote:
>>>
>>> From: Björn Schäpers <bjoern@hazardy.de>
>>>
>>> Sorry for the noise, this is the current version of the Patch.
>>>
>>> -- >8 --
>>> 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 available, instead of the embedded (and possibly outdated) database.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 <bjoern@hazardy.de>
>>> ---
>>>   libstdc++-v3/src/c++20/tzdb.cc | 35 ++++++++++++++++++++++++++++++++++
>>>   1 file changed, 35 insertions(+)
>>>
>>> diff --git a/libstdc++-v3/src/c++20/tzdb.cc b/libstdc++-v3/src/c++20/tzdb.cc
>>> index 6e244dc656d..cdc487af3f5 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 +1150,35 @@ 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))
>>> +           {
>>> +             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.resize(dll_path_view.size()
>>> +                                 + remaining_path.size());
>>> +                     auto iter
>>> +                         = ranges::copy(dll_path_view, path.begin()).out;
>>> +                     ranges::copy(remaining_path, iter);
>>
>> Why not simply:
>>
>>    path = dll_path_view;
>>    path += remaining_path;
>>
>> ?
> 
> And reserve not resize before that.
> 

Just the style I prefer and no additional size check (though the compiler might 
remove that anyway). I can change that.

>>
>>> +                   }
>>> +               }
>>> +           }
>>> +       }
>>>   #endif
>>>         if (!path.empty())
>>>          path.append(filename);
>>> --
>>> 2.50.0
>>>
>