Re: [PATCH v4 7/9] make dprintf.exp pass in always-async mode

[Pedro Alves <palves at redhat dot com>]

On 10/22/2013 06:59 PM, Tom Tromey wrote:
> When target-async is enabled, dprintf.exp fails.
> 
> This happens because run_inferior_call causes gdb to forget that it is
> running in sync_execution mode, so something like a breakpoint
> condition that makes an inferior call causes gdb to enter fully async
> mode.

It'd be great if we had a test that exercised this without
relying on how dprintf is implemented behind the scenes.

> This patch fixes the problem by noticing when gdb was in
> sync_execution mode in run_inferior_call, and taking care to restore
> this state afterward.
> 
> Built and regtested on x86-64 Fedora 18.
> 
> 	PR cli/15718:
> 	* infcall.c: Include event-top.h.
> 	(run_inferior_call): Call async_disable_stdin if needed.
> ---
>  gdb/infcall.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/gdb/infcall.c b/gdb/infcall.c
> index 19af044..7398913 100644
> --- a/gdb/infcall.c
> +++ b/gdb/infcall.c
> @@ -36,6 +36,7 @@
>  #include "ada-lang.h"
>  #include "gdbthread.h"
>  #include "exceptions.h"
> +#include "event-top.h"
>  
>  /* If we can't find a function's name from its address,
>     we print this instead.  */
> @@ -398,6 +399,8 @@ run_inferior_call (struct thread_info *call_thread, CORE_ADDR real_pc)
>  
>    TRY_CATCH (e, RETURN_MASK_ALL)
>      {
> +      int was_sync = sync_execution;
> +
>        proceed (real_pc, GDB_SIGNAL_0, 0);
>  
>        /* Inferior function calls are always synchronous, even if the
> @@ -407,6 +410,11 @@ run_inferior_call (struct thread_info *call_thread, CORE_ADDR real_pc)
>  	{
>  	  wait_for_inferior ();
>  	  normal_stop ();
> +	  /* If gdb was previously in sync execution mode, then ensure
> +	     that it remains so.  normal_stop calls
> +	     async_enable_stdin, so reset it again here.  */
> +	  if (was_sync)
> +	    async_disable_stdin ();
>  	}
>      }

Hmm, I was a worried about what would happen if the inferior
exits, or some other thread hits a breakpoint, or something
else like that.  Like, what enables back stdin in that case?
So an error is always thrown, and we'll hit the INF_REG_EVENT error
handling inf-loop.c:inferior_event_handler, which re-enables back
stdin and the prompt.  So the change is OK with me, but I'd
like to have this mentioned in the comment.

Thanks,
-- 
Pedro Alves