[LLVMdev] x86 unwind support[MESSAGE NOT SCANNED]

Andrew Haley
Mon, 20 Jul 2009 13:53:14 -0000

Kenneth Uildriks wrote:
>> Let's go back a bit.  Your claim is that there is no need to unwind
>> frame-by-frame, an unwind simply needs to make a single jump to an
>> invoke instruction and restore the context (which in x86 is just 6
>> registers).  (This is, more or less, what longjmp() does.)  Duncan
Sands
>> explained to you why that wouldn't work, saying "if you throw
an
>> exception using your proposed unwind implementation, then it
wouldn't
>> be caught by dwarf catch/cleanup regions".
>>
>> He's right.  You can't just jump to the invoke instruction, you
must
>> also pop any cleanups.  This is nothing to do with C++, and it has
>> nothing to do with whether a language has stack-allocated objects.
>
> But don't all functions that require cleanups issue invokes rather
> than calls?

I don't think so: any function in any language that has pthreads bindings
can call pthread_cleanup_push() .

Andrew.