Exceptions

[Mark Mitchell <mmitchell at usa dot net>]

I'm a bit confused about the current C++ exception-handling support in
egcs.  Here's what I know:

o There are setjmp()/longjmp() based exceptions, which are on by
  default.  There are problems here bacause the flow graphs don't
  look quite right; this leads to bogus warnings about clobbered
  variables, or incorrect code.

o There are non-sjlj exceptions, which should be faster, but which 
  do not work on all targets, since they require that call stacks
  are self-describing.

I don't know whether the second variety works in general, and whether
or not there are problems with the flow graphs there as well, and for
what platforms they are supported.

I also note that the info files have no information about any of this,
so far as I can tell.  Even -fno-exceptions is not documented there.

If someone knows, I'd appreciate being told the answers to the
questions I've given above, and as complete as possible a summary of
the problems.  I'd also like to know if anyone is currently working on
this stuff.  

I'll offer in return to update the info documentation with what I
learn, at the very least.  If no one else is looking at the problem,
and I have time, I'll perhaps take a look at trying to fix some of the
problems.

Thank you,

-- 
Mark Mitchell		mmitchell@usa.net
Stanford University	http://www.stanford.edu