On Sat, 24 Dec 2022, 11:35 Iain Sandoe via Libstdc++, <libstdc++@gcc.gnu.org>
wrote:

>  If this is not the right place to export the symbol (or you do not want
>  to export it in the general case), I can always add a platform-specific
>  file for it.  So far, tested on x86_64-darwin21, wider testing will
>  follow over the holidays.
>
>  OK for trunk?
>

I'd like to check if this causes the undefined weak symbol to be exported
on ELF, but I suppose that doesn't really cause any harm if it is. The
symbol name is in our own namespace so can't clash with user symbols. We
can't declare that function in a header, because "zoneinfo_dir_override" is
not a reserved name so could clash with user macros (we could prefix it
with underscores, but since it's possible to override it without the
library providing a declaration, I think it would be "nicer" to not use an
ugly reserved name for something users are supposed to define themselves).





 Iain
>
>  --- 8< ---
>
> This symbol needs to be visible in the library interface for Darwin
> to override it with a user-provided one.
>
> Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
>
> libstdc++-v3/ChangeLog:
>
>         * config/abi/pre/gnu.ver (GLIBCXX_3.4):
>         Add __gnu_cxx::zoneinfo_dir_override().
> ---
>  libstdc++-v3/config/abi/pre/gnu.ver | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/libstdc++-v3/config/abi/pre/gnu.ver
> b/libstdc++-v3/config/abi/pre/gnu.ver
> index 570ffca8710..bd4ab450652 100644
> --- a/libstdc++-v3/config/abi/pre/gnu.ver
> +++ b/libstdc++-v3/config/abi/pre/gnu.ver
> @@ -1104,6 +1104,9 @@ GLIBCXX_3.4 {
>      # std::uncaught_exception()
>      _ZSt18uncaught_exceptionv;
>
> +    # __gnu_cxx::zoneinfo_dir_override()
> +    _ZN9__gnu_cxx21zoneinfo_dir_overrideEv
> +
>    # DO NOT DELETE THIS LINE.  Port-specific symbols, if any, will be here.
>
>    local:
> --
> 2.37.1 (Apple Git-137.1)
>
>