[PATCH] Invalid unpoisoning of stack redzones on ARM

[Jakub Jelinek]

On Tue, Oct 29, 2013 at 12:25:33PM +0000, Richard Sandiford wrote:
> >> Any updates on this one? Note that this bug is a huge blocker for
> >> using AddressSanitizer on ARM platforms.
> >
> > Sorry for the delay, I finally found time to look at it.
> > While your patch fixes the issue, I wonder if for the case where
> > shadow_mem before the asan_clear_shadow call is already of the form
> > (mem (reg)) it isn't better to just adjust next asan_clear_shadow
> > base from the end of the cleared region rather than from the start of it,
> > because the end will be already in the right pseudo, while with your
> > approach it needs to be done in a different register and potentially
> > increase register pressure.  So here is (completely untested) alternate fix:
> 
> Hmm, it just seems wrong to be assigning to registers returned by force_reg
> and expand_binop though.  Would this variation be OK?

Why?  If it is a pseudo, it is certainly a pseudo that isn't used for
anything else, as it is the result of (base >> 3) + constant, if it isn't a
pseudo, then supposedly it is better not to just keep adding the offsets to
a base and thus not to use the end address from asan_clear_shadow.
Your patch would force using the end address even if shadow_base
is initially say some_reg + 32, I think it is better to use shadow_mem
some_reg + 72 next time instead of some_other_reg + 40.

	Jakub