Re: proposed instruction trace support in SystemTap

[fche at redhat dot com (Frank Ch. Eigler)]

Maynard Johnson <maynardj@us.ibm.com> writes:

> [...]
> I work with Dave, and I told him I would cover for him on this issue
> while he's away from the office for a bit.  

Thanks!

> > [...] We could have a
> > guard expression like dtrace's /.../ - though we would probably just
> > spell it thusly:
> >     probe PROBEPOINT if (expr) { } [...]
> Yes, I think this construct could be very useful.

OK, anyone dissenting?

> > [...]
> In fact, the raw trace data is well-defined by the existing ITrace
> tool I mentioned above.  Of course, this definition is
> negotiable. [...]

My point is more whether this definition ought to be hidden, and be
hard-coded for interoperation with your itrace post-processing tool.


> > Is there an existing kernel API for management of these
> > [single-stepping] registers/fields?
> Unfortunately, not that I'm aware of. [...]

OK, then how is it done at all?  You just set saved control register
bits by hand?  Available on how many architectures?  How is the
callback received?  How does this handle issues such as more than one
itrace session operating at a time?

- FChE