Re: [Valgrind-users] Re: Valgrind detection of non-aligned memory accesses?

[Zeljko V. <zel...@av...>]

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On Thu, Aug 14, 2003 at 11:29:44AM -0700, John Reiser wrote:
> >Lucky for us, so does the x86.  There is a flag you can set in some
> >register or other which makes the CPU trap on unaligned access.  So long
> >as we don't do it internally, you could set that and watch all the
> >unaligned accesses in your program (even without Valgrind).
> 
> Yes, it's the AC [Alignment Check] bit of the processor flags,
> which is bit 18 (the bit with positional value (1<<18) or 0x40000).
> It checks for unaligned access in user mode.
> 
But not only AC. As I recall, some other bit in some control register (CR)
must be enabled also. And even then, AC occurs only in user mode (ring 3).

- -- 
v
Zeljko Vrba, dipl. ing.
http://pgp.mit.edu:11371/pks/lookup?op=vindex&search=0x3B375F1C

zel...@av...
Advanced Simulation Technologies
http://www.avl.com

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