Re: Display of read/access watchpoints when HAVE_NONSTEPPABLE_WATCHPOINT

[Paul Koning <pkoning at equallogic dot com>]

>>>>> "Ulrich" == Ulrich Weigand <weigand@i1.informatik.uni-erlangen.de> writes:

 >> My experience was that the old code worked if you had only a
 >> watchpoint active, but it would produce the wrong results if you
 >> had both watchpoints and breakpoints active.  The reason was that
 >> the scan for matching break/watch points would conclude that the
 >> target break had happened due to a non-matching watchpoint and
 >> would proceed, rather than break.

 Ulrich> But this error scenario should only apply to read/access
 Ulrich> watchpoints, never write watchpoints.  A write watchpoint
 Ulrich> should never be misdetected ...

Sorry, I wasn't clear in the explanation, faulty memory.

The actual explanation: a "hard breakpoint" ("break" instruction
assembled-in, rather than inserted by gdb) is detected by the fact
that nothing matches in the scan of the break/watch point list.

The original code would work correctly if only breakpoints were set.
If watchpoints were also set, a hard breakpoint would be treated as a
mismatched watchpoint, and gdb would just continue rather than
stopping.  

 >> That doesn't seem like a good idea.  Why would it be reasonable to
 >> treat the two differently?

 Ulrich> Because a write watchpoints can be handled without hardware
 Ulrich> support to provide the address, while read/access watchpoints
 Ulrich> fundamentally cannot be.

Except for the issue that Daniel just mentioned (foo = 1; foo = 1;)

       paul