Re: [PATCH] libstdc++: Ignore filesystem::canonical errors for /etc/localtime [PR125467]

On Thu, 13 Aug 2026, 07:10 Tomasz Kamiński, <[email protected]> wrote:

> While the errors from realpath (and readlink before
> r17-2048-gcc195f7b11a406)
> are ignored (str is left empty), the filesystem::canonical path thrown
> exception in such situation. This patch ignores the error consistently,
> by using error_code overload of filesystem::canonical.
>
> The !ec check before str assignment is not necessary, as standard requires
> that filesystem::canonical returns empty path, but I think it helps
> readability.
>
> libstdc++-v3/ChangeLog:
>
>         PR libstdc++/125467
>         * src/c++20/tzdb.cc (tzdb::current_zone): Use error_code overload
>         of filesystem::canonical to ignore errors.
> ---
> I agree there is inconsistency in treatment of filesystem errors, and
> they seem to be consistently ignored on other paths. Torbjorn could you
> confirm that this addresses the issue.
> We will still need to wait for Jonathan to OK this.
>
> Not sure how to test this branch. But tested this change locally.
> OK for trunk?
>

OK

The newlib bug should still be fixed.



>  libstdc++-v3/src/c++20/tzdb.cc | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/libstdc++-v3/src/c++20/tzdb.cc
> b/libstdc++-v3/src/c++20/tzdb.cc
> index e358b778e2d..0d004a8a6fe 100644
> --- a/libstdc++-v3/src/c++20/tzdb.cc
> +++ b/libstdc++-v3/src/c++20/tzdb.cc
> @@ -2335,8 +2335,10 @@ constinit tzdb_list::_Node::NumLeapSeconds
> tzdb_list::_Node::num_leap_seconds;
>         str = p;
>        }
>  #else
> -    string sbuf = std::filesystem::canonical("/etc/localtime").string();
> -    str = sbuf;
> +    error_code ec;
> +    string sbuf = std::filesystem::canonical("/etc/localtime",
> ec).string();
> +    if (!ec)
> +      str = sbuf;
>  #endif
>
>      if (!str.empty() && str != "/etc/localtime")
> --
> 2.55.0
>
>