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

[Pedro Alves <palves@redhat.com>]

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.

> @@ -1933,6 +1956,8 @@ darwin_nat_target::attach (const char *args, int from_tty)
>    inferior_appeared (inf, pid);
>    inf->attach_flag = 1;
>  
> +  add_thread_silent (inferior_ptid);
> +
>    darwin_attach_pid (inf);
>  
>    darwin_suspend_inferior (inf);

This surely is not related to "run" and/or fork-inferior.c

Thanks,
Pedro Alves