breakpoint extension for remote protocol, take II

J.T. Conklin
Tue Jun 22 11:46:00 GMT 1999

>>>>> "Andrew" == Andrew Cagney <> writes:
Andrew> o the breakpoint protocol be made official
Andrew> 		using the ``z/Z'' character (think cntrl-z)

Andrew> 		GDB would also get a command allowing it to
Andrew> 		use ``b/B'' as a compatibility character.

As far as I'm concerned, there is no reason to maintain b/B for
backwards compatibility.  I deliberately avoided adding the breakpoint
extensions to production code until the specification was settled.

Andrew> 		DOES ANYONE OBJECT TO ``[zZ]''?

Not as such.

Andrew> o the ``,LLLL'' be made non-optional.

Andrew> 		For software breakpoints it would indicate the
Andrew> 		size of the instruction (in hex bytes) that
Andrew> 		needs to be patched.

Ugly, but I don't know how to get around it on MIPS/ARM.  Perhaps this
could still be omitted on all of the other architectures that only
have a single breakpoint instruction.  What would be the semantics 
of a request to add a N byte breakpoint when the architecture does
not have a N byte breakpoint instruction?

Andrew> 		J.T. would this break your existing stub code?

Nothing in my stub is in concrete.

Andrew> o the ``LLLL'' for hardware-breakpoints and
Andrew> 		watchpoints be clarified to explain that it
Andrew> 		indicates the region to be watched.

I'd like to make sure the specification is very flexible.  For
example, a processor that didn't support access watchpoints but had
MMU support that could turn off read/write on a page basis could be
used to implement this feature.

However, there is still one problem with my proposal which I have not
had time to address.  As the remote protocol is a datagram protocol
and the breakpoint extension adds run-time state to the stub, there
must be some mechanism to handle dropped and duplicate packets.
Perhaps a sequence number argument needs to be added to the command
and the response.


The same sequence number scheme could be used for this, and any other
stateful commands that might be added in the future.


J.T. Conklin
RedBack Networks

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