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Date: Wed, 21 Oct 2009 19:46:51 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: [Qemu-devel] Re: [PATCH] qemu: work around for "posix-aio-compat"
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>, qemu-devel@nongnu.org

On Wed, Oct 21, 2009 at 07:44:14PM +0200, Paolo Bonzini wrote:
>
>>> I suggest trying to make the sigset_t static, since that generates
>>> exactly the same code as the "nohang" case, and exactly the same stack
>>> layout as the "hang" case.
>
> (In case this wasn't clear: the sigfillset of a static sigset_t should  
> hang, proving that it's stack layout that comes to the rescue).
>
>>> The next obvious step would be placing a
>>> watchpoint somewhere.
>>
>> Yes, but where?
>
> At every word of the sigset (using gdb commands to disable/enable the  
> watchpoints around the sigfillset, you avoid spurious triggers).

Not sure how do you mean. When would I enable the watchpoint?

>  One of  
> those words will be overwritten if an overrun would have smashed the  
> stack.  If it does not fire, s/sigfillset/sigemptyset/ in case it was  
> writing 0xffffffff.  If it still does not fire, dunno. :-(
>
> Paolo