On 02/13/2018 04:22 PM, Paolo Bonzini wrote:
On 13/02/2018 14:35, Jakub Jelinek wrote:
On Tue, Feb 13, 2018 at 12:21:55PM +0100, Jakub Jelinek wrote:
On Tue, Feb 13, 2018 at 12:15:36PM +0100, Paolo Bonzini wrote:
The issue is that the ASAN_CHECK doesn't exist at early DSE time, and
thus causes the store to disappear.


If it was DSE removing the stores before asan pass, then it would FAIL
before as well.

Sorry, while ASAN_CHECK is introduced late, ASAN_MARK is present there
already from the gimplification.

Yeah, and it keeps everything alive.

For use after scope, I guess a lot of the stores after end of scope
(rather than reads) are something DSE could consider removing.
So, shall we just disable DSE on vars where their address "escapes"
through ASAN_MARK when -fsanitize-address-use-after-scope?

But the stores _are_ dead; it's only the ASAN_CHECK that isn't.  Hence
the idea of doing the entire instrumentation very early.

Generally, dead stores could be eliminable when stored before the
corresponding ASAN_MARK poison (but even ASAN_MARK with "..W.." will
prevent those) and uneliminable when stored after ASAN_MARK poison.

For the "fn spec" for now, I'd just go with "..R.." for ASAN_CHECK and
NULL for ASAN_MARK for now.

I'm a bit scared of that even, :) especially in stage4.  If you think
it's safe enough, I can give it a shot, but honestly I wouldn't have
much time to deal with the fallout now (hence the quick revert).

Let me do it tomorrow.

Martin


Paolo


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