-fexceptions? -fasync-unwind-tables?

Ulrich Weigand weigand at immd1.informatik.uni-erlangen.de
Mon May 19 18:29:58 CDT 2003

Gregory Turner wrote:

> On Monday 19 May 2003 05:14 pm, Ulrich Weigand wrote:
> > Note that g++ exception handling with dwarf2 works quite different from
> > MSVC exception handling -- the former hooks exception processing into
> > the dwarf2 frame 'personality' routines, while the latter uses the
> > exception frame chain anchored in the TEB ...
> Ideally, some compiler will emerge which would generate the same undocumented 
> unwind tables used by msvc to do it... that way tryblocks from native dlls 
> and wine dlls, and MSVC++ and XYZ++ exceptions could all get along 
> swimmingly...

Note that there are two quite different things involved here, as far as
GCC extensions are concerned.

First, we'd need a GCC extension to support the __try/__finally and/or
__try/__except syntax in the C (and possibly C++) frontend.  This would
hook into the regular GCC exception infrastructure (which on most targets
uses dwarf2 frame personality routines to actually handle exceptions).

However, this wouldn't be enough, as those exception wouldn't be 
integrated with Windows/Wine 'SEH' based exceptions.  So you'd really
want *another* GCC extension to get GCC to use a different exception
handling infrastructure (for both the new __try/__finally *and* for
regular C++ exceptions as well), which would be compatible with
Windows exception handling.

As the SEH based exception handling is large undocumented, and also
very much platform specific, I'd doubt the GCC folks would be happy
about the latter part ...

A different approach might be to add code to Wine to 'interface'
between the two exception infrastructures e.g. by catching all
Windows exceptions and rethrowing them as GCC exceptions or vice
versa at every Windows/Unix code boundary.  I'm not sure whether
this would actually work, though (and even if, it probably won't
be very efficient).  

Alternatively, the Wine exception unwinding could try to follow 
both the SEH TEB-anchored frame chain *and* the dwarf2 CFI stack 
unwinding chain and intermix between the two as required (this
is actually similar to a proposal on the GCC list how to handle
C++ cleanups intermixed with pthread cancellation handlers).


  Dr. Ulrich Weigand
  weigand at informatik.uni-erlangen.de

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