Re: [ppc-linux-nat]: set access flag for h/w watchpoint even if it is only read or write

Daniel Jacobowitz
2006-07-06T13:20:34Z

On Fri, Jun 09, 2006 at 11:40:26PM +0800, Wu Zhou wrote:
> Hello all,
>
> I found a bug in the current ppc-linux h/w watchpoint implementation:
> when we set read watchpoint to some expression, if there are any write
> operation to it before a read operation is hit, watchpoint_check will see
> that its value is changed. So user won't see the watchpoint is hit.
>
> I make one change to the SET_DEBUGREG operation: even if it is only
> read or write watchpoint, we still set access flag. Then, no matter
> what operation is on the watched address, a SIGTRAP will be triggered.
> The gdb code itself can determine if it is a write operation or read
> operation. If it is write, watchpoint_check routine can update the
> bs->value to the latest.

Eli, you're the most familiar with watchpoint support; do you have any
comment on this?

I know that we've encountered the same problem on other architectures
before (I can't recall exactly when, but I definitely remember Ulrich
fixing it for S/390, in the same way). It seems strange to me. Many
targets can tell us what sort of watchpoint was hit; we could do
something like extend target_stopped_data_address to also return what
sort of watchpoint was triggered, if it knows.

> - case hw_write:
> - /* Set write and translate bits. */
> - dabr_value |= 6;
> - break;

Wu, I bet you don't really want to change this case. Write watchpoints
are the most common, and I think they'll work fine even if they don't
trigger on reads - since some platforms can't even trigger on reads.
This would be a big slowdown.

--
Daniel Jacobowitz
CodeSourcery