[LLVMdev] x86 unwind support[MESSAGE NOT SCANNED]

Kenneth Uildriks kennethuil at gmail.com
Mon Jul 20 06:39:59 PDT 2009

> 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.
> Andrew.

But don't all functions that require cleanups issue invokes rather
than calls?  Unwind or __cxa_throw would just go to the nearest one,

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