Re: [asan] Emit GIMPLE directly, small cleanups

[Xinliang David Li <davidxl@google.com>]

On Mon, Oct 15, 2012 at 11:12 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Mon, Oct 15, 2012 at 10:48:13PM -0700, Xinliang David Li wrote:
>> Another error checking feature is to poison stack vars on entry and
>> exit of the lexical scope to catch uninit variable reference and out
>> of scope references:
>>
>> S* sp;
>>   {
>>     S s;
>>     sp = &s;
>>   }
>>   .. *sp ...
>>
>> This is relatively easy to do in gcc thanks to the clobber statement.
>> In Clang/LLVM, it is in the wishlist:
>> http://code.google.com/p/address-sanitizer/issues/detail?id=83
>
> That is not easy at all unfortunately, CLOBBER isn't sufficient for that.
> You have the points where the variable looses value, but there aren't
> similar markup statement where it gets into scope again.
> See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54770#c3

I don't get it.  Clobber marks the end of lifetime of a variable so it
is safe to emit code to really clobber its value -- otherwise how
would clobber based slot sharing work?

David

>
>         Jakub