[llvm-dev] asan for allocas on powerpc64

[Kostya Serebryany via llvm-dev]

+Maxim and Yuri, as I think this is their code.

On Thu, Nov 12, 2015 at 3:02 AM, Jay Foad <jay.foad at gmail.com> wrote:

> (Resending with the correct mailing list address.)
>
> Hi,
>
> Currently test/asan/TestCases/alloca_vla_interact.cc is XFAILed for
> powerpc64. I've had a look at why it doesn't work. I think the only
> problem is in the call to __asan_allocas_unpoison that is inserted at
> the end of the "for" loop (just before a stackrestore instruction).
>
> The call function is created something like this (paraphrasing from
> lib/Transfoms/Instrumentation/AddressSanitizer.cpp):
>
>   // call __asan_allocas_unpoison(uptr top, uptr bottom);
>   // NB "top" here means lowest address and "bottom" means highest!
>
>   IRB.CreateCall(
>     AsanAllocasUnpoisonFunc,
>     {
>       IRB.CreateLoad(DynamicAllocaLayout),
>       IRB.CreatePointerToInt(SaveRestoreInst->getOperand(0), IntptrTy)
>     }
>   );
>
> I think the problem is that the operand to stackrestore is the new
> native sp register value to restore, and this code is assuming that
> that will be a higher address than all the allocas that are being
> unallocated. But on PowerPC64, the native sp is always lower than the
> address of the most recent alloca by MaxCallFrameSize bytes, to leave
> space for outgoing call arguments. So I think the second argument to
> __asan_allocas_unpoison needs to be SaveRestoreInst->getOperand(0) +
> MaxCallFrameSize, but I don't know how to implement that.
>
> Thoughts?
>
> Thanks,
> Jay.
>
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