Ping: Re: [PATCH] libgcc: fix SEH C++ rethrow semantics [PR113337]

[Matteo Italia <matteo@mitalia.net>]

Ping! That's a one-line fix, and you can find all the details in the 
bugzilla entry. Also, I can provide executables built with the affected 
toolchains, demonstrating the problem and the fix.

Thanks,
Matteo

Il 17/01/24 12:51, Matteo Italia ha scritto:
> SEH _Unwind_Resume_or_Rethrow invokes abort directly if
> _Unwind_RaiseException doesn't manage to find a handler for the rethrown
> exception; this is incorrect, as in this case std::terminate should be
> invoked, allowing an application-provided terminate handler to handle
> the situation instead of straight crashing the application through
> abort.
>
> The bug can be demonstrated with this simple test case:
> ===
> static void custom_terminate_handler() {
>      fprintf(stderr, "custom_terminate_handler invoked\n");
>      std::exit(1);
> }
>
> int main(int argc, char *argv[]) {
>      std::set_terminate(&custom_terminate_handler);
>      if (argc < 2) return 1;
>      const char *mode = argv[1];
>      fprintf(stderr, "%s\n", mode);
>      if (strcmp(mode, "throw") == 0) {
>          throw std::exception();
>      } else if (strcmp(mode, "rethrow") == 0) {
>          try {
>              throw std::exception();
>          } catch (...) {
>              throw;
>          }
>      } else {
>          return 1;
>      }
>      return 0;
> }
> ===
>
> On all gcc builds with non-SEH exceptions, this will print
> "custom_terminate_handler invoked" both if launched as ./a.out throw or
> as ./a.out rethrow, on SEH builds instead if will work as expected only
> with ./a.exe throw, but will crash with the "built-in" abort message
> with ./a.exe rethrow.
>
> This patch fixes the problem, forwarding back the error code to the
> caller (__cxa_rethrow), that calls std::terminate if
> _Unwind_Resume_or_Rethrow returns.
>
> The change makes the code path coherent with SEH _Unwind_RaiseException,
> and with the generic _Unwind_Resume_or_Rethrow from libgcc/unwind.inc
> (used for SjLj and Dw2 exception backend).
>
> libgcc/ChangeLog:
>
>          * unwind-seh.c (_Unwind_Resume_or_Rethrow): forward
>          _Unwind_RaiseException return code back to caller instead of
>          calling abort, allowing __cxa_rethrow to invoke std::terminate
>          in case of uncaught rethrown exception
> ---
>   libgcc/unwind-seh.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/libgcc/unwind-seh.c b/libgcc/unwind-seh.c
> index 8ef0257b616..f1b8f5a8519 100644
> --- a/libgcc/unwind-seh.c
> +++ b/libgcc/unwind-seh.c
> @@ -395,9 +395,9 @@ _Unwind_Reason_Code
>   _Unwind_Resume_or_Rethrow (struct _Unwind_Exception *exc)
>   {
>     if (exc->private_[0] == 0)
> -    _Unwind_RaiseException (exc);
> -  else
> -    _Unwind_ForcedUnwind_Phase2 (exc);
> +    return _Unwind_RaiseException (exc);
> +
> +  _Unwind_ForcedUnwind_Phase2 (exc);
>     abort ();
>   }
>