[patch] Fix a double collect of static tracepoint

[Pedro Alves]

On 12/20/2011 04:29 PM, Yao Qi wrote:
> Hi,
> This patch fixes a problem that static tracepoint's collect is performed
> twice (one from gdbserver and the other one from IPA), when there is
> another regular tracepoint setting at the same address.
>
> When program hits a trap, gdbserver will iterate all tracepoints (in
> tracepoint.c:tracepoint_was_hit) and call collect_data_at_tracepoint if
> condition is null or result is true. In this iteration, static
> tracepoint is in this list, so gdbserver will collect for this static
> tracepoint, even the trap is caused by another regular tracepoint, which
> is set at the same address.  The collect of static tracepoint is
> performed for the first time.
>
> Then, gdbserver resumes program, and UST marker/probe is executed.  In
> gdb_probe, the collect of static tracepoint is performed for the 2nd
> time.  So we have one static tracepoint, "hit" once, but get two trace
> frames finally.
>
> This patch is to fix this problem described above.  I'll send out
> another patch for test case, and this patch fixes one fail in it.

Yeah.  We instead step over fast tracepoints to solve this problem,
to give a consistent view of when a tracepoint is hit to the user.
Although it would be possible to step over static tracepoints
similarly, it wouldn't work, because of the possibility of a
"collect $_sdata" action, which can only be done by the
inferior.  IOW, if the inferior stops at a static tracepoint's
address today, one with a "collect $_sdata", and you do "tdump",
you'll see that $_sdata will be missing or unavailable, or maybe even
an error.

So, okay.  Thanks.

>
> -- Yao (齐尧)
>
>
> 0007-Don-t-collect-for-static-tracepoint.patch
>
>
> 2011-12-20  Yao Qi<yao@codesourcery.com>
>
> 	* tracepoint.c (tracepoint_was_hit): Don't collect for
> 	static tracepoint.
> ---
>   gdb/gdbserver/tracepoint.c |    8 ++++++--
>   1 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/gdb/gdbserver/tracepoint.c b/gdb/gdbserver/tracepoint.c
> index ac07db9..1cc4b4b 100644
> --- a/gdb/gdbserver/tracepoint.c
> +++ b/gdb/gdbserver/tracepoint.c
> @@ -4276,8 +4276,12 @@ tracepoint_was_hit (struct thread_info *tinfo, CORE_ADDR stop_pc)
>       {
>         /* Note that we collect fast tracepoints here as well.  We'll
>   	 step over the fast tracepoint jump later, which avoids the
> -	 double collect.  */
> -      if (tpoint->enabled&&  stop_pc == tpoint->address)
> +	 double collect.  However, we don't collect for static
> +	 tracepoints here, because UST markers are compiled in program,
> +	 and probes will be executed in program.  So static tracepoints
> +	 are collected in there.   */
> +      if (tpoint->enabled&&  stop_pc == tpoint->address
> +	&&  tpoint->type != static_tracepoint)
>   	{
>   	  trace_debug ("Thread %s at address of tracepoint %d at 0x%s",
>   		       target_pid_to_str (tinfo->entry.id),


-- 
Pedro Alves