Re: [RFA 4/5] Darwin: fix thread ptid started by fork_inferior

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

On 2018-08-22 12:10, Pedro Alves wrote:
> On 08/22/2018 11:11 AM, Xavier Roirand wrote:
> 
>> 
>> diff --git a/gdb/darwin-nat.c b/gdb/darwin-nat.c
>> index 96f70cf..9ad4a87 100644
>> --- a/gdb/darwin-nat.c
>> +++ b/gdb/darwin-nat.c
>> @@ -344,8 +344,22 @@ darwin_check_new_threads (struct inferior *inf)
>>  	  pti->gdb_port = new_id;
>>  	  pti->msg_state = DARWIN_RUNNING;
>> 
>> -	  /* Add the new thread.  */
>> -	  add_thread_with_info (ptid_t (inf->pid, 0, new_id), pti);
>> +	  if (old_nbr == 0 && new_ix == 0)
>> +            {
>> +	      /* A ptid is created when the inferior is started (see
>> +                 fork-child.c) with lwp=tid=0.
> 
> It looks like this patch was written against an older gdb,
> because fork-child.c doesn't add a thread nowadays.  For GNU/Linux, 
> it's
> inf-ptrace.c that adds the initial thread, but only after
> fork_inferior returns (inf_ptrace_target::create_inferior).
> 
> But were is that equivalent code in darwin-nat.c?
> 
> /me looks.
> 
> Answer: it's nowhere.  It does not exist.
> 
> So, when then shared fork-child.c was created a while ago,
> the add_thread call was moved to darwin-nat.c's target_create_inferior
> implementation.  But, later on, Simon removed that add_thread call 
> with:
> 
>  commit db665f427ca781d631d9e29b1bb744fb11ffcbba
>  Author:     Simon Marchi <simon.marchi@ericsson.com>
>  AuthorDate: Tue Jun 27 10:55:36 2017 +0200
>  Commit:     Simon Marchi <simon.marchi@ericsson.com>
>  CommitDate: Tue Jun 27 10:56:53 2017 +0200
> 
>     darwin: Do not add a dummy thread
> 
> (Weird, I can't find that patch on the list's archives, even
> though I received a local copy.)
> 
> It sounds to me like you need to reevaluate the patch from
> scratch, because its premise is invalid.

Hmm I had not considered that, I did that a while ago and had completely 
forgotten about it.  I'll try to take a look tomorrow, when I have 
access to the Mac machine.  Maybe the spurious SIGTRAP I saw when 
running was caused by the bug fixed by patch 5/5.

Simon