Re: (remote) hellishly slow single stepping over library calls

["Theodore A. Roth" <troth at openavr dot org>]

On Fri, 16 May 2003, Kris Warkentin wrote:

:) When debugging using our QNX pdebug remote protocol and single stepping over
:) a library call like printf, it takes a LOOOONG time.  I'm talking like two
:) or three minutes.  A 'next' is fine but looking at the output of running our
:) pdebug server in verbose mode, gdb is doing step, step, step, all the way
:) through the whole library call.  Every single step results in fetching
:) registers and there is a huge amount of wire traffic generated.
:)
:) This didn't happen with older (ie 5.0) gdbs which didn't seem to know how to
:) single step through our shared lib code but now that it does, this is pretty
:) painful.  Obviously it makes more sense to 'next' over a library call,
:) especially if you don't want to go into it but the question is, can anyone
:) think of a way to optimize this?  I though of putting in a hack like:
:)
:) if (reg == PC_REGNUM)
:)     only_get_pc();
:)
:) to avoid fetching the whole regset but it probably won't make that much
:) difference since there's still a packet over the wire each time and most
:) regsets fit in one packet anyway.
:)
:) Would this problem also exist with the normal remote protocol?  (stupid
:) users...clicking step instead of next....;-)

Not sure if this is totally related (how does pdebug differ from rsp?)
but maybe a solution could help avr users too.

Some sort of optimization here would be boon for avr users. In our
case we use gdb to talk to our avarice program
(http://sourceforge.net/projects/avarice) which talks to a jtagice box
which in turn talks to the actual target device via a jtag interface.
Single stepping is painfully slow: step, wait 1-5 seconds, step, etc.

The bottleneck for us not so much sending info over the wire via rsp,
but in reading the registers from the device via jtag. If we could
reduce the number registers that need to be read at each step, I think
it could speed things up.

For comparision, I also have a avr simulator which is controlled by
gdb via rsp. Single stepping in the simulator is fairly fast (feels
almost as fast as stepping a native program).

Ted Roth