RE: [PATCH v4 3/9] btrace: Use binary search to find instruction.

["Metzger, Markus T" <markus dot t dot metzger at intel dot com>]

> -----Original Message-----
> From: Wiederhake, Tim
> Sent: Wednesday, January 4, 2017 1:46 PM
> To: gdb-patches@sourceware.org
> Cc: Metzger, Markus T <markus.t.metzger@intel.com>
> Subject: [PATCH v4 3/9] btrace: Use binary search to find instruction.

Hello Tim,

> @@ -1818,6 +1820,11 @@ btrace_fetch (struct thread_info *tp)
> 
>        btrace_clear_history (btinfo);
>        btrace_compute_ftrace (tp, &btrace);
> +
> +      VEC_truncate (btrace_fun_p, btinfo->functions, 0);
> +
> +      for (bfun = btinfo->begin; bfun != NULL; bfun = bfun->flow.next)
> +	VEC_safe_push (btrace_fun_p, btinfo->functions, bfun);

I'd truncate BTINFO->FUNCTIONS before calling btrace_compute_ftrace.

The function may throw - either due to errors or because the user lost patience
and interrupted trace processing.  This would leave us with stale pointers.

We should really run this loop also in case btrace_compute_ftrace was
interrupted.  The trace will be incomplete but we won't discard what we
already computed.


> +  for (;;)
> +    {
> +      const unsigned int average = lower + (upper - lower) / 2;
> +
> +      bfun = VEC_index (btrace_fun_p, btinfo->functions, average);
> +
> +      if (number < bfun->insn_offset)
> +	{
> +	  upper = average - 1;
> +	  continue;
> +	}
> +
> +      if (number >= bfun->insn_offset + ftrace_call_num_insn (bfun))
> +	{
> +	  lower = average + 1;
> +	  continue;
> +	}
> +
> +      break;
> +    }

It is OK to assume that there are no holes in the numbering.  We may want
to spell this out in a comment.

Thanks,
Markus.

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