Andrea Corallo via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> Richard Earnshaw <richard.earns...@foss.arm.com> writes:
>
>> On 27/09/2022 16:24, Kyrylo Tkachov via Gcc-patches wrote:
>>>
>>>> -----Original Message-----
>>>> From: Andrea Corallo <andrea.cora...@arm.com>
>>>> Sent: Tuesday, September 27, 2022 11:06 AM
>>>> To: Kyrylo Tkachov <kyrylo.tkac...@arm.com>
>>>> Cc: Andrea Corallo via Gcc-patches <gcc-patches@gcc.gnu.org>; Richard
>>>> Earnshaw <richard.earns...@arm.com>; nd <n...@arm.com>
>>>> Subject: Re: [PATCH 9/15] arm: Set again stack pointer as CFA reg when
>>>> popping if necessary
>>>>
>>>> Kyrylo Tkachov <kyrylo.tkac...@arm.com> writes:
>>>>
>>>>> Hi Andrea,
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Gcc-patches <gcc-patches-
>>>>>> bounces+kyrylo.tkachov=arm....@gcc.gnu.org> On Behalf Of Andrea
>>>>>> Corallo via Gcc-patches
>>>>>> Sent: Friday, August 12, 2022 4:34 PM
>>>>>> To: Andrea Corallo via Gcc-patches <gcc-patches@gcc.gnu.org>
>>>>>> Cc: Richard Earnshaw <richard.earns...@arm.com>; nd <n...@arm.com>
>>>>>> Subject: [PATCH 9/15] arm: Set again stack pointer as CFA reg when
>>>> popping
>>>>>> if necessary
>>>>>>
>>>>>> Hi all,
>>>>>>
>>>>>> this patch enables 'arm_emit_multi_reg_pop' to set again the stack
>>>>>> pointer as CFA reg when popping if this is necessary.
>>>>>>
>>>>>
>>>>> From what I can tell from similar functions this is correct, but could
>>>>> you
>>>> elaborate on why this change is needed for my understanding please?
>>>>> Thanks,
>>>>> Kyrill
>>>>
>>>> Hi Kyrill,
>>>>
>>>> sure, if the frame pointer was set, than it is the current CFA register.
>>>> If we request to adjust the current CFA register offset indicating it
>>>> being SP (while it's actually FP) that is indeed not correct and the
>>>> incoherence we will be detected by an assertion in the dwarf emission
>>>> machinery.
>>> Thanks, the patch is ok
>>> Kyrill
>>>
>>>>
>>>> Best Regards
>>>>
>>>> Andrea
>>
>> Hmm, wait. Why would a multi-reg pop be updating the stack pointer?
>
> Hi Richard,
>
> not sure I understand, isn't any pop updating SP by definition?
Back on this,
compiling:
=======
int i;
void foo (int);
int bar()
{
foo (i);
return 0;
}
=======
With -march=armv8.1-m.main+fp -mbranch-protection=pac-ret+leaf -mthumb -O0 -g
Produces the following asm for bar.
bar:
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 1, uses_anonymous_args = 0
pac ip, lr, sp
push {r3, r7, ip, lr}
add r7, sp, #0
ldr r3, .L3
ldr r3, [r3]
mov r0, r3
bl foo
movs r3, #0
mov r0, r3
pop {r3, r7, ip, lr}
aut ip, lr, sp
bx lr
The offending instruction causing the ICE (without this patch) when
emitting dwarf is "pop {r3, r7, ip, lr}".
The current CFA reg when emitting the multipop is R7 (the frame
pointer). If is not the multipop that has the duty to restore SP as
current CFA here which other instruction should do it?
Best Regards
Andrea
