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Date: Wed, 24 Nov 2004 20:50:17 +1300
From: Danny Smith <dannysmith AT clear DOT net DOT nz>
Subject: Re: stdcall lib functions with exception throwing callbacks vs Dwarf2 EH
To: Richard Henderson <rth AT redhat DOT com>
Cc: gcc AT gcc DOT gnu DOT org, Cygwin <cygwin AT cygwin DOT com>,
   mingw-dvlpr <mingw-dvlpr AT lists DOT sourceforge DOT net>
Reply-to: Danny Smith <dannysmith AT users DOT sourceforge DOT net>
Message-id: <000c01c4d1fa$3f297fd0$e56d65da@DANNY>
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References: <001701c4d1ab$949322e0$0a6d65da AT DANNY> <20041124003240 DOT GA6028 AT redhat DOT com>

Richard Henderson wrote:
> On Wed, Nov 24, 2004 at 11:27:11AM +1300, Danny Smith wrote:
>> Before I pull any more hair out trying, does any one have any hints
>> on how to use an MD_FALLBACK_FRAME_STATE_FOR to workaround ...
>
> That would be wrong.
>
> I think the most likely explanation is that there's a bug in the
> dwarf2 generator for stdcall functions with -fomit-frame-pointer,
> and the problem should be attacked there.
>
> If you've got a call that takes 12 bytes of arguments on the stack
> and pop them on return, then the unwind info should look like
>
> # DW_CFA_GNU_args_size 12
> call foo
> # DW_CFA_def_cfa_offset <previous value - 12>
>
>

Umm, actually I don't think it is stdcall thing at all.

When I reran the testcase after doing other things both the cdecl and
stdcall functions resulted in uncaught exceptions, I can't explain the
success with cdecl in my earlier report,

Sorry for the noise.

If I compile the callback-using library code with -fexceptions using a
DW2 enabled compiler, then both calling conventions work, as expected.

So is it a general requirements of DW2 EH that functions that are passed
callbacks as args  be compiled with -fexceptions,  if the callbacks may
throw?  I don't see how else they could work

Danny

> r~


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