Re: [PATCH] S/390: Improve storing asan frame_pc

[Richard Sandiford <richard.sandiford@arm.com>]

Segher Boessenkool <segher@kernel.crashing.org> writes:
> On Tue, Jul 02, 2019 at 03:55:56PM +0200, Ilya Leoshkevich wrote:
>> > Am 02.07.2019 um 15:39 schrieb Jakub Jelinek <jakub@redhat.com>:
>> > On Tue, Jul 02, 2019 at 03:33:28PM +0200, Ilya Leoshkevich wrote:
>> >>> Am 02.07.2019 um 15:19 schrieb Segher Boessenkool <segher@kernel.crashing.org>:
>> >>> 
>> >>> On Tue, Jul 02, 2019 at 08:02:16AM -0500, Segher Boessenkool wrote:
>> >>>> On Tue, Jul 02, 2019 at 10:51:54AM +0200, Ilya Leoshkevich wrote:
>> >>>>> +#undef TARGET_INSN_ALIGNMENT
>> >>>>> +#define TARGET_INSN_ALIGNMENT 16
>> >>>> 
>> >>>> There already is FUNCTION_BOUNDARY for something similar, which fits in
>> >>>> well with STACK_BOUNDARY, PARM_BOUNDARY, many more *_BOUNDARY.  I realise
>> >>>> you may prefer a hook, but as long as we aren't getting rid of all the
>> >>>> other macros, what's the point?
>> >>> 
>> >>> And maybe LABEL_BOUNDARY is bettter for this than INSN_BOUNDARY as well?
>> >> 
>> >> Can’t we just use FUNCTION_BOUNDARY then?
>> >> I think .LASANPC is always emitted at the beginning of a function.
>> > 
>> > Isn't e.g. the hotpatch sequence emitted before it?
>> 
>> You are right, with -fpatchable-function-entry it’s moved.
>> 
>> So, I guess I should stick with the current approach.
>> I could change TARGET_INSN_ALIGNMENT hook to INSN_BOUNDARY macro if that
>> would better match the current design.  I would still call it INSN, and
>> not LABEL, because LABEL can refer to data.
>
> On some archs LABEL_BOUNDARY can be bigger than INSN_BOUNDARY (just like
> FUNCTION_BOUNDARY can be even bigger, like on 390 :-) )
>
> Either will work for your purposes afaics.
>
> LABEL in RTL is always a CODE_LABEL I think?  Maybe CODE_LABEL_BOUNDARY
> would make it clearer, it's not like a short name for this is useful
> anyway.

IIUC the new value is effectively a mandatory/guaranteed minimum value of
align_labels/LABEL_ALIGN that applies even in blocks optimized for size.
So IMO sticking with *_ALIGNMENT would be better.

Thanks,
Richard