Re: [PATCH 5/8] Insert breakpoint even when the raw breakpoint is found

[Pedro Alves <palves@redhat.com>]

On 03/04/2016 10:44 AM, Yao Qi wrote:
> When GDBserver inserts a breakpoint, it looks for raw breakpoint, if
> the raw breakpoint is found, increase its refcount, and return.  This
> doesn't work when it steps over a breakpoint using software single
> step and the underneath instruction of breakpoint is branch to self.
> 
> When stepping over a breakpoint on ADDR using software single step,
> GDBserver uninsert the breakpoint, so the corresponding raw breakpoint
> RAW's 'inserted' flag is zero.  Then, GDBserver insert single step
> breakpoint at the same address ADDR because the instruction is branch
> to self, the same raw brekapoint RAW is found, and increase the
> refcount.  However, the raw breakpoint is not inserted, and the
> program won't stop.
> 
> gdb/gdbserver:
> 
> 2016-03-04  Yao Qi  <yao.qi@linaro.org>
> 
> 	* mem-break.c (set_raw_breakpoint_at): Insert raw breakpoint
> 	when its refcount is increased.
> ---
>   gdb/gdbserver/mem-break.c | 17 ++++++++++++++++-
>   1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/gdbserver/mem-break.c b/gdb/gdbserver/mem-break.c
> index b06f8e9..73c5e8a 100644
> --- a/gdb/gdbserver/mem-break.c
> +++ b/gdb/gdbserver/mem-break.c
> @@ -411,7 +411,22 @@ set_raw_breakpoint_at (enum raw_bkpt_type type, CORE_ADDR where, int kind,
>     if (bp != NULL)
>       {
>         bp->refcount++;
> -      return bp;
> +
> +      if (!bp->inserted)
> +	{
> +	  *err = the_target->insert_point (bp->raw_type, bp->pc, bp->kind,
> +					   bp);
> +	  if (*err != 0)
> +	    {
> +	      if (debug_threads)
> +		debug_printf ("Failed to insert breakpoint at 0x%s (%d).\n",
> +			      paddress (where), *err);
> +	      free (bp);

If this raw breapoint already existed, and we just bumped the
refcount, then this free leaves those other breakpoints with
a stale pointer.

But I'd like to defer this patch until we reach a conclusion on the
previous one on the gdb side.

> +	      return NULL;
> +	    }
> +	  bp->inserted = 1;
> +	}
> +	return bp;
>       }
>   
>     bp = XCNEW (struct raw_breakpoint);
> 


-- 
Thanks,
Pedro Alves