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Re: [Qemu-devel] [PATCH] vl.c: Implement SIGILL signal handler for trigg

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH] vl.c: Implement SIGILL signal handler for triggering SIGSEGV
Date: Thu, 05 Sep 2013 17:06:58 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130805 Thunderbird/17.0.8

On 09/05/2013 04:50 PM, Anthony Liguori wrote:
>> +    int *p = NULL;
>> +
>> +    *p = 0xDEADBEEF;
> I won't repeat the questions from Paolo and Lazlo (I share their
> confusion) but will simply add that you cannot rely on NULL address
> accessing causing a SEGV.  Even with all the use of volatile in the
> world, there's no guarantee this is going to crash.

If you want to guarantee that a write would cause a SEGV, then you have
to use mmap(MAP_ANONYMOUS|MAP_PRIVATE) + mprotect(PROT_NONE) to get a
valid unwritable pointer that will reliably fault, rather than hoping
that NULL (or any other low-valued intptr_t cast to void*) is
sufficiently protected.  But I also echo the question: why is raise()

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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