32-bit Thumb-2 breakpoints

[Catalin Marinas]

On Wed, 2010-02-03 at 15:02 +0000, Matthieu CASTET wrote:
> Russell King - ARM Linux a écrit :
> > On Wed, Feb 03, 2010 at 11:52:22AM +0000, Catalin Marinas wrote:
> >> On Wed, 2010-02-03 at 00:50 +0000, Daniel Jacobowitz wrote:
> >>> On Tue, Feb 02, 2010 at 10:43:22PM +0000, Russell King - ARM Linux
> >>> wrote:
> >>>> Umm, today there were patches posted using hardware support for
> >>>> breakpoints / watchpoints.  I've not read through those patches
> >>>> yet, but in light of hardware support, do we really need this patch
> >>>> anymore?
> >>> Yes, it's unrelated.  Hardware breakpoints are a constrained resource,
> >>> but we can insert unlimited software breakpoints (and often need to
> >>> exceed the hardware breakpoint limit).
> >> I agree, we still need support for software breakpoints.
> >>
> >> The main benefit of hardware debugging support is for watchpoints.
> >
> > Software breakpoints are a pain in the backside if you have threaded
> > programs, because when you insert a breakpoint into one thread, it's
> > active in all threads - you can't insert a breakpoint into only one
> > thread.
> 
> An annoying things about software breakpoints is that gdb doesn't
> understand arm kernel helper (for atomic operation/tls). And when it try
> to set breakpoint here it fails...

That kernel helpers are in a page is not writable (or COW-able). Maybe
with hardware breakpoints this could be solved.

-- 
Catalin