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Re: Hardware watchpoint support for MIPS?


Paul Koning wrote:
"David" == David Daney <ddaney@avtrex.com> writes:

David> Paul Koning wrote:
>>>>>>> "David" == David Daney <ddaney@avtrex.com> writes:
>>
David> GDB has had support for i386 debug registers on linux for
David> quite some time now.
>>
David> I was wondering if anyone has worked on similar support for
David> the hardware debug support available in some MIPS processors?
>> Yes, I have it on MIPS/sb1.
>>


David> Great!

 David> Could you be more specific?  Like where are the kernel patches
 David> to expose the debugs registers to ptrace and the gdb patches
 David> to take advantage of them?

As Daniel pointed out, the kernel and ptrace changes are really the
issue here.

We modified a NetBSD 1.6.2 kernel, adding watchpoint primitives to its
gdb stub (for kernel debug) and also to its ptrace. The ptrace stuff
was a bit hairy because you have to context switch that state.


I don't think I had to change gdb at all, except perhaps for setting
the #define symbols to turn the feature on and describe its behavior
correctly with respect to single stepping.

Well, there was a bug at least in the earlier 6.x gdb releases where
the code to sort out breakpoints and watchpoints would come up with
the wrong answer if you hit a watchpoint while a breakpoint was also
active (even at some entirely different address).

And yes, the notion of watchpoint is in the MIPS architecture but the
specifics vary among implementations.  I have seen several, and they
are close enough that a single gdb talking the same remote protocol
works with all of them, but the target end does change somewhat from
one MIPS flavor to the next.


OK, thanks. I mistakenly thought that you already had it working on mips[el]-linux and I might just be able to drop it in (It's OK to dream isn't it?).


David Daney


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