_Unwind_Backtrace vs. _Unwind_RaiseException unwinding

[Roy Krischer <rkrische at plg dot uwaterloo dot ca>]

Hi,

I've been playing around with _Unwind_Backtrace for a C++ project of 
mine. Ideally, I would like to call the personality routine from 
_Unwind_Backtrace to decode the lsda for me, and I can certainly do it 
through the trace function.

The problem that I have, however, is that the unwinding that 
_Unwind_Backtrace produces is different from the one 
_Unwind_RaiseException produces. More specifically, the contexts created 
by _Unwind_Backtrace have the first few register locations  NULLed, so 
when I run the personality routine in _UA_CLEANUP_PHASE mode, it tries 
to dereference those (reg[0] and reg[2] on my architecture) null 
pointers and crashes.

What is so fundamentally different about _Unwind_Backtrace and 
_Unwind_RaiseException, that _Unwind_RaiseException produces 'complete' 
contexts, while Backtrace does not? Is it because _Unwind_RaiseException 
uses __builtin_eh_return and this causes the compiler to generate the 
proper information?

How can I trick _Unwind_Backtrace into producing the same contexts 
and/or using the personality routine and it behaving just like during 
exception handling (minus installing the context at the end, of course)?

Any help would be greatly appreciated

  Roy