Re: [PATCH] gdbserver/linux-low: carry over stop_expected flag after exec (avoid spurious SIGSTOPs)

[Simon Marchi <simon.marchi@polymtl.ca>]

On 2026-06-26 14:04, Pedro Alves wrote:
> On 2026-06-26 19:00, Simon Marchi wrote:
>> On 2026-06-26 13:35, Pedro Alves wrote:
>>>> +      unsigned long execing_tid = event_ptid.lwp ();
>>>> +      if (ptrace (PTRACE_GETEVENTMSG, event_ptid.lwp (), (PTRACE_TYPE_ARG3) 0,
>>>> +		  &execing_tid) != 0)
>>>> +	execing_tid = event_ptid.lwp ();
>>>
>>> This gave me pause -- this is setting execing_tid to the event lwp if ptrace fails.
>>> But execing_tid is already initialized to the event lwp.  I think it'd be clearer not
>>> to initialize it, like:
>>>
>>>       unsigned long execing_tid;
>>>       if (ptrace (PTRACE_GETEVENTMSG, event_ptid.lwp (), (PTRACE_TYPE_ARG3) 0,
>>> 		  &execing_tid) != 0)
>>> 	execing_tid = event_ptid.lwp ();
>>
>> Well, the question then is: what if the ptrace call fails?  It probably
>> never fails, but we still have to think about it.  execing_tid would be
>> used uninitialized.  I see three options:
> 
> I'm confused with the question.  In the snippet I proposed, if ptrace fails,
> then we set execing_tid:
> 
>       unsigned long execing_tid;
>       if (ptrace (PTRACE_GETEVENTMSG, event_ptid.lwp (), (PTRACE_TYPE_ARG3) 0,
> 		  &execing_tid) != 0)
> 	execing_tid = event_ptid.lwp ();  <<< ptrace failed.
> 
> So this behaves exactly like your original code, just without the redundant
> initialization.
> 
> Am I missing something?

No, I did miss that assignment.

I will add a comment to say that we fall back to the leader if ptrace
fails, not ideal but should be correct most of the time.

Simon