Re: [PATCH v1 2/2] gdb: rely on the first non-exited thread TPID when reading Linux procfs files

[Matthieu Longo <matthieu.longo@arm.com>]

On 24/08/2026 17:25, Matthieu Longo wrote:
> On 24/08/2026 16:29, Matthieu Longo wrote:
>> On 20/08/2026 16:48, Simon Marchi wrote:
>>> On 7/28/26 10:33 AM, Matthieu Longo wrote:
>>>> +/* Return a PTID that identifies the current process and can be used to
>>>> +   access procfs safely.
>>>> +
>>>> +   The returned PTID is that of the thread-group leader whenever it is
>>>> +   still alive.  If the leader has already exited, the PTID of the first
>>>> +   non-exited thread in the current inferior is returned instead.
>>>> +   This ensures that the returned PTID always refers to a live thread
>>>> +   whose procfs entries are present and populated.  */
>>>> +static ptid_t
>>>> +get_process_reference_ptid (bool verbose = false)
>>>> +{
>>>> +  /* Get the current thread.  */
>>>> +  thread_info *thr = inferior_thread ();
>>>> +
>>>> +  /* Construct the PTID of the thread-group leader.  On Linux,
>>>> +     the leader's LWP ID is equal to the process ID.  */
>>>> +  ptid_t leader_ptid (thr->ptid.pid (), thr->ptid.pid ());
>>>> +
>>>> +  /* Use the thread-group leader if it is still alive.  Otherwise, use
>>>> +     the first thread that has not exited.  */
>>>> +  thread_info *leader_thr
>>>> +    = current_inferior ()->find_thread (leader_ptid);
>>>> +  ptid_t ptid = (leader_thr == nullptr
>>>> +		 ? current_inferior ()->first_non_exited_thread ()
>>>> +		 : leader_ptid);
>>>> +
>>>> +  if (!verbose)
>>>> +    return ptid;
>>>> +
>>>> +  if (leader_thr != nullptr)
>>>> +    gdb_printf (_("process %d\n"), leader_ptid.pid ());
>>>> +  else
>>>> +    gdb_printf (_("process %d [Note: information where gathered from LWP %ld " \
>>>> +		  "as the thread-group leader (LWP=%ld) already exited.]\n"),
>>>> +		ptid.pid (), ptid.lwp (), leader_ptid.lwp ());
>>>
>>> I don't think the printfs should be part of this getter function.  Move
>>> it to a separate function called by whoever needs it.  Or just inline
>>> it, it looks like there is just a single caller that needs it
>>> (linux_info_proc).
>>>
>>
>> The idea is to inform the user if a fallback occurs.
>> Now, if I move the printing to another function, I don't have the fetched information anymore, and
>> cannot figure out easily if a fallback happened and using which thread.
>>
>> It is ugly but I could not find better.
>> Do you have a better approach ?
>>> Matthieu
> 
> There is actually a way to figure it out by comparing ptid.pid () and ptid.lwp ().
> 
> Sent r2 addressing your comment.
> https://inbox.sourceware.org/gdb-patches/20260824162155.467233-1-matthieu.longo@arm.com/T/#u
> 
> Matthieu

Sorry, I mistakenly removed you from CC by not clicking the "reply all" button.

Matthieu