Re: [PATCH 1/3] Avoid find_thread_ptid with null_ptid

[Pedro Alves <palves@redhat.com>]

On 10/01/2018 04:53 PM, Tom Tromey wrote:
>>>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes:
> 
> Pedro> This patch prepares for the change, by avoiding passing down null_ptid
> Pedro> to find_thread_ptid or to functions that naturally use it
> 
> Should find_thread_ptid assert this?

I didn't think it's useful, since the code will end up like this:

struct thread_info *
find_thread_ptid (ptid_t ptid)
{
  inferior *inf = find_inferior_ptid (ptid);
  if (inf == NULL)
    return NULL;
  return find_thread_ptid (inf, ptid);
}

and null_ptid hits that assertion in:

struct inferior *
find_inferior_pid (int pid)
{
  /* Looking for inferior pid == 0 is always wrong, and indicative of
     a bug somewhere else.  There may be more than one with pid == 0,
     for instance.  */
  gdb_assert (pid != 0);


But I can add it if you prefer.

> 
> Pedro>    if (print_inferior_events)
> Pedro> -    printf_unfiltered (_("[New inferior %d (%s)]\n"),
> Pedro> -		       inf->num,
> Pedro> -		       target_pid_to_str (ptid_t (pid)));
> Pedro> +    {
> Pedro> +      if (pid != 0)
> Pedro> +	printf_unfiltered (_("[New inferior %d (%s)]\n"),
> Pedro> +			   inf->num,
> Pedro> +			   target_pid_to_str (ptid_t (pid)));
> Pedro> +      else
> Pedro> +	printf_unfiltered (_("[New inferior %d]\n"), inf->num);
> 
> I wonder if it is possible for an RSP implementation to say that the
> inferior has PID 0.

GDB would break down badly.  Throughout we assume pid == 0 means the
inferior/process is not started.

The RSP docs say:

"In addition, the remote protocol supports a multiprocess feature in
which the @var{thread-id} syntax is extended to optionally include both
process and thread ID fields, as @samp{p@var{pid}.@var{tid}}.
The @var{pid} (process) and @var{tid} (thread) components each have the
format described above: a positive number with target-specific
                        ^^^^^^^^^^^^^^^^^
interpretation formatted as a big-endian hex string, literal @samp{-1}
to indicate all processes or threads (respectively), or @samp{0} to
                                                     ^^^^^^^^^^^^^^
indicate an arbitrary process or thread.  Specifying just a process, as
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Thanks,
Pedro Alves