[parisc-linux] Single-stepping

[law@redhat.com]

  In message <200011151949.OAA22929@hiauly1.hia.nrc.ca>you write:
  > >   I've been helping Alan Modra out with kernel changes to support
  > > single stepping for gdb.  Paul Bame suggested I bounced our ideas
  > > off you in case you (or anyone else) had any comments.  I havn't
  > > actually committed my changes yet.
  > > 
  > > The basic approach is to use the recovery counter to generate
  > > a trap every instruction.  The scheme is complicated because a
  > > suspended process may or may not return to user space via an RFI.
  > 
  > I really don't know enough to comment on the implementation choice.  Why
  > did you decide on this approach as opposed to inserting breaks and
  > enabling the taken branch branch trap (T)?  It would appear that the recove
  > ry
  > counter was intended to provide software recovery from hardware faults
  > in fault tolerant systems.  Possibly, Grant could comment on whether
  > it is actually useful for this purpose.
Err, we tried that at the UofU in our mach port to the PA -- there's a problem
with that scheme, though I don't remember precisely what it was.  I believe
there were cases where the recovery counter doesn't trigger a trap, possibly
due to nullified instructions.

You might look at the UofU BSD code, which I believe used breakpoints and
branch taken traps instad.

jeff