[RFC/RFA] gdbreplay V2.0

[Michael Snyder <msnyder at specifix dot com>]

Here's a new contribution -- I call it gdb-freeplay, an 
improved and less restrictive version of gdbreplay.  Its
something I've been playing around with for some time now.

This is a remote protocol logger/replayer, that works in
principal just like gdbreplay -- it even uses the same
logfiles, with no changes or enhancements.

However, where gdbreplay constrains you in the replay session
to giving *exactly* the same commands, in *exactly* the same
sequence, as were used in the recorded session, gdb-freeplay
frees you of that constraint -- you can change the order of
the commands, or skip them entirely, even skip ahead past an
arbitrary number of execution events to get to the "interesting"
ones.  

You use step and next just like you did in the recorded
session, but now you can set a breakpoint and continue on
ahead to a later part of the session, even if you did not
do so in the original session.  You can even next over a
function call that you originally stepped into -- so long
as you also stepped out of it.  Or you can skip out with
"finish", even if you continued to debug the function 
interminably in the original session.

You can print any variable(s) or registers that you 
examined before, in any order, even combine them into
expressions that were not used in the recorded session
(so long as all the values of the expression were evaluated).
In many ways, it's a lot like tracepoint debugging.

I picture it being useful for gdb testing -- we might 
even create hand-crafted "sessions" and use it to play
them back to explicitly test parts of the remote protocol.

I can also picture a user sending you a binary and a
recorded log in which a bug happened -- you could debug
it even with a cross-debugger, lacking the appopriate
hardware (or simulator or what have you) -- and even if
the recorded log was 50 megabytes long, you could skip
ahead to the interesting bits.

But frankly, I just wrote it because it was fascinating to do...

Michael

PS I've already written back-ends for x86, MIPS64, and x86-64.
Most other target architectures should be fairly easy to add, 
and it will work with anything that uses the remote protocol.

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