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From: Alexander Monakov <amonakov@ispras.ru>
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Subject: Re: [PATCH] replace 'hlt' by 'ud2' in i386/x32/x86_64 a_crash
 implementations
Date: Fri, 17 Apr 2015 11:12:20 +0300 (MSK)
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On Fri, 17 Apr 2015, Rich Felker wrote:

> On Thu, Apr 16, 2015 at 08:58:59PM +0300, Alexander Monakov wrote:
> > ---
> > ud2 is also what GCC and Clang use to implement __builtin_trap()
> > 
> > ud2 causes SIGILL rather than SIGSEGV; SIGSEGV is more likely to have a custom
> > signal handler installed
> 
> I've pondered instead using:
> 
> 	push $-1
> 	mov $175,%eax
> 	xor %ebx,%ebx
> 	mov %esp,%ecx
> 	int $128
> 	hlt // or ud2?
> 
> This should be uncatchable but it's moderately larger. 

An argument in favor of plain hlt/ud2 is that registers and memory are
preserved, in case someone will be analyzing the coredump.

Alexander