Re: [PATCH] Add __builtin_stack_top

["H.J. Lu" <hjl.tools@gmail.com>]

On Wed, Aug 19, 2015 at 5:51 AM, Segher Boessenkool
<segher@kernel.crashing.org> wrote:
> On Wed, Aug 19, 2015 at 05:23:41AM -0700, H.J. Lu wrote:
>> >>> >> > You might have a reason why you want the entry stack address instead of the
>> >>> >> > frame address, but you didn't really explain I think?  Or I missed it.
>> >>
>> >> What would a C program do with this, that it cannot do with the frame
>> >> address, that would be useful and cannot be much better done in straight
>> >> assembler?  Do you actually want to expose the argument pointer, maybe?
>> >
>> > Yes, we want to use the argument pointer as shown in testcases
>> > included in my patch.
>>
>> Where do we stand on this?  We need the hard stack address at
>> function entry for x86 without using frame pointer.   I added
>> __builtin_stack_top since __builtin_frame_address can't give
>> us what we want.  Should __builtin_stack_top be added to
>> middle-end or x86 backend?
>
> Sorry for not following up; I thought my suggestion was obvious.
>
> Can you do a __builtin_argument_pointer instead?  That should work
> for all targets, afaics?

To me, stack top is easier to understand and argument pointer isn't
very clear.  Does argument pointer exist when there is no argument?

But I can live with it.  I will update my patch.

Thanks.

-- 
H.J.