Re: [PATCH] gdbserver: keep event_child and current_inferior in sync

[Pedro Alves <palves at redhat dot com>]

On 01/27/2014 08:01 PM, Doug Evans wrote:
> Hi.
> 
> I ran into this while debugging some testsuite failures in my rewrite
> of speeding up gdbserver attach.
> 
> linux_wait_1 calls linux_wait_for_event, and one of the things
> linux_wait_for_event does is set current_inferior (blech, but
> a cleanup for another day).
> 
> linux_wait_1 then sets event_child to the "lwp" part of current_inferior here:
> 
>   event_child = get_thread_lwp (current_inferior);
> 
> and assumes the two remain in sync.
> 
> However later it calls select_event_lwp to pick an event to report back:
> 
> 	  select_event_lwp (&event_child);
> 
> but doesn't update current_inferior.  Later code then does:
> 
>   if (current_inferior->last_resume_kind == resume_stop
>       && WSTOPSIG (w) == SIGSTOP)
> 
> which can use a stale current_inferior.
> 
> In my patch to speed up attach I see the bug more easily because
> I changed the end of the function to be (effectively):
> 
> -  return ptid_of (event_child);
> +  return current_inferior->entry.id;
> 
> FAIL: gdb.threads/watchthreads.exp: threaded watch loop
> FAIL: gdb.threads/watchthreads.exp: combination of threaded watchpoints = 30
> 
> The test fails because a h/w watchpoint is missed, and that happens
> because linux_wait_1 reports the wrong thread.
> 
> 2014-01-27  Doug Evans  <dje@google.com>
> 
> 	* linux-low.c (linux_wait_for_event): Improve comment.
> 	(linux_wait_1): Keep current_inferior in sync with event_child.


OK, thanks!

-- 
Pedro Alves