Re: [PATCH v2 1/5] gdb/aarch64: Implement software single stepping for MOPS instructions

[Luis Machado <luis.machado@arm.com>]

On 5/21/24 22:40, Thiago Jung Bauermann wrote:
> Pedro Alves <pedro@palves.net> writes:
> 
>> On 2024-05-07 03:22, Thiago Jung Bauermann wrote:
>>
>>> The Arm Architecture Reference Manual says that "the prologue, main, and
>>> epilogue instructions are expected to be run in succession and to appear
>>> consecutively in memory".  Therefore GDB needs to treat them as an atomic
>>> instruction sequence, and also can't do displaced stepping with them.
>>
>> Curious on this "can't".  GDB could copy the whole sequence to the displaced
>> stepping buffer, and execute then in one go, and it should work, right?
>>
>> Not suggesting that you should do it as a requisite to the patch, just
>> trying to understand it, in case the issue comes up again in other contexts.
> 
> Yes. I hadn't thought of that, but Luis also gave that idea. He said¹
> that "Regarding displaced stepping, we can disable displaced stepping
> temporarily for these instructions. If we find a convenient way to
> relocate the whole block of MOPS instructions, then we can add that
> later on."
> 
> I'll work on it as a future improvement.
> 

FTR, I'm still happy with enabling this in an upcoming patch. We might have to
think about whether displaced-stepping the block and then getting interrupted
in the middle of executing it needs special handling.