Re: [patch] i386: annotate the rest of entry.s::nmi

From: Jan Beulich
Date: Mon Aug 14 2006 - 02:52:17 EST

>> I understand now, but am still uncertain
>> about the need to annotate FIX_STACK() - especially since you use
>> .cfi_undefined, meaning the return point cannot be established
>> If at all I'd annotate the initial pushes with either just the
>> CFI_ADJUST_CFA_OFFSET, and the final one with one setting back the
>> CFA base to the now adjusted frame. That way, until the pushes are
>> complete the old frame will be used for determining the call
>> and once complete the (full) new state will be used.
>But that's the whole point of the new annotations -- we have just
>overwritten %esp with a new value and the old assumptions are
>completely broken:
> movl TSS_sysenter_esp0+offset(%esp),%esp; \
>After this the old frame cannot be located by using %esp as a base
>and the new frame is incomplete. So the only choice is to make eip
>undefined until the new value is available -- if not then the
>unwinder will try to use whatever random values are on the new frame.
>Either that or I'm still unclear on how unwind works...

Hmm, yes, on a second look I agree.

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