Re: i386 Hardware watchpoints using kgdb-2-2.6.14.tar.gz

Hi Dennis,

I have a patch which sends Z2 packets to kgdb instead sending it to
native gdb.

I have also attached logs that shows the packet dump for h/w watchpoints
and h/w breakpoint.

thanks
-Jitendra
LinSysSoft Technologies
Ask me about KGDB Pro
http://www.linsyssoft.com/Kgdbpro.html

On Wed, 2006-01-11 at 22:22 -0500, Dennis W. Tokarski wrote:
> Hey there Amit,
> 
> Amit Kale wrote:
> > On Saturday 07 Jan 2006 3:46 am, Dennis W. Tokarski wrote:
> > 
> 
> [snip]
> 
> >>2.6.14.3 kernel that I'm using.  I did not include the second patch
> >>which adds kwatch-points--it's a neat feature but not directly
> >>related to kgdb.
> >>
> >>Do you want a copy of the resulting debug register allocation
> >>patch?
> > 
> > 
> > Not sure about this. When soon is kprobes patch expected to make it to the 
> > kernel? If not soon, there isn't any point in using that tmechanism as we 
> > can 
> > survive with some minimal code for that.
> > 
> 
> Is that a change of position?  I incorporated the patch (which I should
> probably have called a "debug register allocation" patch rather than
> a "kprobe" patch) into my work mainly because of your earlier reply
> to Tom's posting on 12/16/05:
> 
> =============
> Amit Kale wrote:
>  > That's a good scheme. We definitely want to use it when enabling 
> watchpoints
>  > in KGDB. Even if it gets accepted in the kernel in a different form or some
>  > other scheme gets accepted, we can quickly change our code base 
> accordingly.
>  >
>  > -Amit
> =============
> 
> I would advocate keeping it.  Certainly something like it becomes necessary
> as soon as anything other than kgdb wants to use the hardware debug registers
> in the kernel.  For anyone debugging a complex problem in user space and the
> kernel concurently (and I've been there many times) it's necessary as well
> to keep user space gdb and kgdb from conflicting.
> 
> The patch is quite minimal, being largely confined to its own header file
> and one arch-specific source file.  It touches the kernel elsewhere only
> where it's unavoidable, and even then only a couple of lines here and there.
> 
> I don't see how it could be reduced without breaking something.
> 
> > 
> 
> [snip]
> 
> >>
> >>Is one of those mechanisms deprecated? I chose for the moment to
> >>use the call through kgdb_ops.
> > 
> > 
> > kgdb_ops function pointers are deprecated. We should be using weak 
> > mechanisms 
> > only. set_breakpoint should also be changed this way.
> > 
> > Milind, can you do the set_breakpoint change?
> > 
> 
> OK, I'll do it that way.  I've captured the essentials of Milands
> patch and will follow that example for the hw_break/watch stuff.
> 
> > 
> >>OK, I lied, there is actually a third issue.  You can't, in
> >>kernel/kgdb.c, just pass the ASCII type code from the Z packet
> 
> [snip]
> 
> > 
> > 
> > I would prefer changing the type of second parameter of set_hw_breakpoint 
> > to 
> > "const char bptype". gdb remote protocol defines the values bptype can take 
> > ('0-4'). Hence they are stable, besides they allow flexibility wrt. 
> > achitecture.
> > -Amit
> > 
> 
> Noted. I'll do that.
> 
>    --Dennis
> 
> > 
> > 
> >>   --Dennis
> >>
> >>Tom Rini wrote:
> >>
> >>>On Fri, Dec 16, 2005 at 10:39:42AM +0530, Amit Kale wrote:
> >>>
> >>>>Dennis,
> >>>>
> >>>>That would be splendid. When a watchpoint is required, no other feature
> >>>>can do the job!
> >>>
> >>>Note that to do this correctly, you have to be aware of other potential
> >>>users.  Prasanna Panchamukhi of the kprobes project forwarded me some
> >>>code that would do this and I'll send that along to the list
> >>>momentarily.
> >>>
> >>>
> >>>>-Amit
> >>>>
> >>>>On Friday 16 Dec 2005 12:41 am, Dennis W. Tokarski wrote:
> >>>>
> >>>>>Hi,
> >>>>>
> >>>>>Amit Kale wrote:
> >>>>>
> >>>>>>On Thursday 15 Dec 2005 8:40 pm, Tom Rini wrote:
> >>>>>>
> >>>>>>>On Fri, Dec 09, 2005 at 12:42:39PM +0530, Amit Kale wrote:
> >>>>>>>
> >>>>>>>>On Thursday 08 Dec 2005 11:13 pm, Dennis W. Tokarski wrote:
> >>>>>
> >>>>>[snip]
> >>>>>
> >>>>>
> >>>>>>>I'm fairly certain we don't support watchpoints, and I don't
> >>>>>>>_think_ we ever did on i386 (we may have on ia64 at some point).  If
> >>>>>>>the packet isn't [zZ][01] we relpy back to GDB that it's unsupported.
> >>>>>
> >>>>>True. But the first problem was gdb wasn't sending out Z packets anyway.
> >>>>>I have a temporary hack to fix that, but gkdb still doesn't set an
> >>>>>execution break point with Z1. It seems instead to set a data access
> >>>>>watchpoint.  As I mentioned before, I was able to manually send Z
> >>>>>packets using the maintenance command and got the same result.
> >>>>>
> >>>>>So, kgdb isn't setting the watchpoint up even when it gets the
> >>>>>right packets.  btw, I'm working exclusively on i386, so that's
> >>>>>all I can speak to.
> >>>>>
> >>>>>Anyway, what I propose to do is look back at an earlier kgdb
> >>>>>which did to all those things correctly--I've got a 2.4.18
> >>>>>kernel here set up that way--and bring the code forward into
> >>>>>the current kgdb for i386.  As part of that I'll handle the
> >>>>>additional Z packets.
> >>>>>
> >>>>>And there's still the problem with gdb itself, and why they
> >>>>>broke Z packets, but I'll take that up on the gdb list.
> >>>>>
> >>>>>
> >>>>>>We didn't have support for official version of gdb watchpoints, though
> >>>>>>one could send "y" packets using "maintenance packet" commands. It
> >>>>>>worked. That was a couple of years ago, I believe. I can't recall when
> >>>>>>we removed support for y packets. Present code doesn't support it for
> >>>>>>sure.
> >>>>>>
> >>>>>>-Amit
> >>>>>
> >>>>>I was certainly working with the macros back in the 2.4.18 days,
> >>>>>but this is the first time I've used kdgb in 2.6.  A lot has
> >>>>>changed, not just with kgdb.
> >>>>>
> >>>>>  --Dennis
> >>>>>
> >>>>>
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hw-watchpoint.patch
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hw-watchpoint.log
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hw-breakpoint.log
Description: Text Data