[compiler-rt] r277874 - Fix two tests in Win64 ASan

[Reid Kleckner via llvm-commits]

On Fri, Aug 5, 2016 at 6:53 PM, David Majnemer <david.majnemer at gmail.com>
wrote:

> On Fri, Aug 5, 2016 at 2:47 PM, Reid Kleckner via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: rnk
>> Date: Fri Aug  5 16:47:46 2016
>> New Revision: 277874
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=277874&view=rev
>> Log:
>> Fix two tests in Win64 ASan
>>
>> Go back to intercepting kernel32!RaiseException, and only go for
>> ntdll!RtlRaiseException if that fails. Fixes throw_and_catch.cc test.
>>
>> Work around an issue in LLVM's win64 epilogues. We end up with an
>> epilogue that looks like this, and it drives the Win64 unwinder crazy
>> until stack overflow:
>>         call    ill_cc!__asan_handle_no_return
>>         xor     eax,eax
>>         add     rsp,40h // epilogue starts
>
>         pop     rbp     // CSR
>>         ud2             // Trap here
>>         ret             // Ret?
>>         nop     word ptr [rax+rax]
>>         sub     rsp,28h // Next function
>>
>
>
> Interesting.  So we started the epilogue but didn't finish it.  Happen to
> have some IR or C lying around?  I'm curious exactly when we decided that a
> ud2 between the pop and the ret was a smart move...
>

It's pretty easy to convince LLVM to put the ud2 there, but it's hard to
build a test case that will cause the Win64 unwinder to fail in the same
way that I observed in this test without the extra conditional control flow
that I added.

$ cat t.cpp
void foo();
int main() { foo(); __builtin_trap(); }

$ clang -S --target=x86_64-windows t.cpp  -fno-omit-frame-pointer -o -
...
        callq   "?foo@@YAXXZ"
        xorl    %eax, %eax
        addq    $32, %rsp
        popq    %rbp
        ud2
        retq
...

I think the issue is that the faulting PC does not appear to be within a
standard epilogue, so the unwinder re-emulates the add 32 and pop rbp.
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