Re: proposed instruction trace support in SystemTap

[Roland McGrath <roland at redhat dot com>]

For user-mode stepping (all you can do via ptrace), this is what the utrace
in-kernel APIs give you.  The in-kernel case has enough different issues
that I think it's appropriate to consider it an entirely separate case.
For that, kprobes already has its fingers in this area of machine-specific
code.  It might make most sense for in-kernel stepping to be an extension
of the kprobes code.  OTOH, with the hw_breakpoint (nee kwatch) work by
Alan Stern <stern@rowland.harvard.edu> we have a second in-kernel case that
(on some machines) wants to get involved with single-stepping.  Perhaps it
makes sense to consolidate the efforts on some shared low-level part that
deals with the stepping part.  Or there may not be enough to be done there
that anything beyond current machine-specific calls and trap notifiers are
really required.  (Off hand I think at least some kind of coordination will
be required to avoid these three things stepping on each other's toes.)


Thanks,
Roland