step out of range

[J.T. Conklin]

I've encounter monitors and ICEs that have a "step out of range"
command where execution continues until a instruction outside of a
range of instructions is about to be executed or a breakpoint is
triggered.  If GDB is able to take advantage of this feature, it won't
have to do multiple single-steps for step, next, until, etc. commands.

This could siginficantly improve interactive debugging performance, as
it eliminates most of the latency from the "step an instruction/ query
registers to check whether we're within the address range/yep we
are/repeat" sequence.

GDB already computes a range of instructions (step_range_start,
step_range_end) that it uses internally when stepping through a range
of instructions.  So it seems that all we need to do is to expose/use
these variables in the target layer.  In fact, the vxWorks RDB target
(remote-vx.c) does exactly this.  But it seems that these values
should be passed through to target_remote() instead of being globals.

Any thoughts?  I'd like to add a step out of range command to the
remote protocol.

        --jtc

-- 
J.T. Conklin
RedBack Networks