[RFA/commit] arm-tdep.c: Do not single-step after hitting a watchpoint.

Pedro Alves palves@redhat.com
Tue Sep 16 15:21:00 GMT 2014

Hi Terry, Marcus,

Can someone at ARM shed some light on this, please?

This thread is here:


And the discussion started in another thread here:


I've just added a test that hopefully helps with this, btw:


I'm also wondering whether Aarch64 needs adjustment as well.

Pedro Alves

On 09/16/2014 02:09 PM, Luis Machado wrote:
> On 09/16/2014 09:48 AM, Joel Brobecker wrote:
>>>> I think the experiments that were run showed that QEMU is in fact
>>>> correct and should NOT be changed.
>>> Do we know what the Linux kernel's behavior on this one is? I wonder
>>> what the stopped data address shows.
>>> Someone with access to a board with a relatively new kernel could
>>> try that and rule it out, otherwise we risk fixing something for
>>> QEMU/bare metal and breaking things for Linux.
>> When I tested on GNU/Linux, watchpoints simply did not work
>> (silently ignored, no signal).  I was using an old kernel (2012),
>> though; but that's all I had access to.  But, all in all, baremetal
>> should be our most reliable source of info, though,no? - no software
>> layer to murky the waters.
> It is hard to tell. ARM's documentation is not clear. For example, this 
> is probably where the stopped data address should be coming from:
> --
> WFAR - Watchpoint Fault Address Register
> The WFAR is updated to indicate the address of the instruction that 
> accessed the watchpointed address:
> - the address of the instruction + 8 in ARM state
> - the address of the instruction + 4 in Thumb® state
> --
> So it seems in line with what we are seeing? The program being trapped 
> two instructions after the data fault?
> If it stops just a single instruction after the data fault, then someone 
> (probe, emulator or kernel) may be trying to help GDB by decrementing 
> the data fault address.
> Luis

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