Re: [PATCH, RFC] Enable libsanitizer on powerpc{,64}

[Konstantin Serebryany <konstantin.s.serebryany@gmail.com>]

On Mon, Nov 19, 2012 at 6:49 PM, Peter Bergner <bergner@vnet.ibm.com> wrote:
> On Mon, 2012-11-19 at 15:29 +0100, Jakub Jelinek wrote:
>> On Fri, Nov 16, 2012 at 05:08:06PM -0600, Peter Bergner wrote:
>> > One question that I have is that the toplev.c test for port support
>> > tests for !FRAME_GROWS_DOWNWARD.  The rs6000 port has FRAME_GROWS_DOWNWARD
>> > defined as (flag_stack_protect != 0), so ASAN only works when we use
>> > -fstack-protector.  Is there a technical reason why FRAME_GROWS_DOWNWARD
>> > must be false?
>>
>> It would be way too much work to support FRAME_GROWS_DOWNWARD.
>
> Do you you have a pointer or a reference that describes why ASAN
> relies on that?

The only part where I know for sure that asan relies on stack growing
down is the custom unwinder, which is not applicable to PowerPC
anyway.
Another suspect is the way we poison redzones in the stack frame and
report an error if one found, but It may actually just work.
If the tests pass, I would say it indeed just works.


> I don't doubt you are correct, but for my own
> education, I'd like to know the reason.
>
>
>> IMHO far simple for targets like ppc is to define
>> FRAME_GROWS_DOWNWARD as (flag_stack_protect != 0 || flag_address_sanitizer != 0).
>
> That looks like a better idea than what I was thinking of, so
> I'll go ahead and add that to our target patch.  Thanks!
>
> Peter
>
>
>