Re: Tracepoint enhancements

[Stan Shebs <stan@codesourcery.com>]

Michael Snyder wrote:
> [...] a checkpoint
> represents a machine state.  If there are multiple machines,
> that complicates the picture -- but basically gdb is saying
> to the target "I want to be able to return to the state that
> you are in *right now*".
Hmm, that is a significant wrinkle to the execution history theory. 
Basically it's not possible to know reliably whether the execution state 
of one CPU comes sooner or later than the state of another CPU - their 
clocks can't be guaranteed to be sync'ed to a sub-instruction level. 
It's a little like a distributed version control system, where each 
repository has its own version numbers, and any ordering derives from 
explicit push/pull instructions. Each inferior can have a reliable 
execution history, but if you want to go back to state X on CPU 1, you 
either just affect the one inferior, or expect that other inferiors will 
go back to the closest available state in their histories.

Stan