Display of read/access watchpoints when HAVE_NONSTEPPABLE_WATCHPOINT
Orjan Friberg
orjan.friberg@axis.com
Fri Apr 16 09:46:00 GMT 2004
Eli Zaretskii wrote:
>>Date: Thu, 15 Apr 2004 15:23:59 +0200
>>From: Orjan Friberg <orjan.friberg@axis.com>
>>
>>The test program (repeated below) *does* work for i386 (though I didn't
>>say that), because it also stops when foo is written (thus updating the
>>value of foo when watchpoint_check is called), so by the time it stops
>>when the second read happens the value hasn't changed since the last
>>time and GDB decides it's a valid hit.
>
>
> Right; sorry I forgot about that. It's been a long time since I
> hacked that part of GDB.
Apologies; I didn't mean to imply that that was obvious. (I certainly
didn't know that was why it worked on the i386 when I posted the example
in the first place.)
>>1. Add a check if the target cannot set "pure" read watchpoints to the
>>b->type == bp_read_watchpoint check at WP_VALUE_CHANGED (my
>>interpretation of Eli's suggestion).
>
>
> On balance, this is probably the best solution, although it's not
> quite clean. The ability to set read watchpoints would be part of the
> architecture vector, right?
Yes, I think so. Also, this seems like the least intrusive change.
(Nevertheless, since you were kind enough to comment on the other
suggestions, I'll continue the discussion of them.)
>>2. Somehow don't update the value in watchpoint_check when it's a false
>>hit. (Then the b->type == bp_read_watchpoint check at WP_VALUE_CHANGED
>>isn't needed.)
>
>
> Wouldn't this reintroduce the bug that I was trying to solve back
> then? That is, will GDB still DTRT when both rwatch and watch are set
> at the same variable?
You're right; this won't work. I failed to account for the fact that
the code *relies* on the i386 stopping (and updating the value) when
writing to an rwatched variable.
In addition, I'm not sure how we'd detect a false hit for the i386 (the
"somehow" part). For my upcoming target, I have bits telling me if it
was a read or write that caused the exception.
>>3. Add some distinction between "wanted watchpoint type" and "actual
>>watchpoint type".
>
>
> Any specific ideas how to do that? For that matter, what is ``wanted
> watchpoint type'', and how can we decide that?
The idea was that when inserting a watchpoint, target_insert_watchpoint
would return the type of watchpoint that was actually inserted. So, for
the i386 an insertion of a read watchpoint would return an access
watchpoint (if I've understood correctly). The breakpoint struct would
then have an additional field storing this returned value.
In bpstat_stop_status, the code would then be something like
case WP_VALUE_CHANGED:
if (b->type == bp_read_watchpoint
&& b->actual_type == bp_access_watchpoint)
/* Don't stop. */
...
I'll have a look at implementing the first suggestion. Thanks.
--
Orjan Friberg
Axis Communications
More information about the Gdb-patches
mailing list