Process Debugging questions

[Dag-Erling Smørgrav]

Jeremie Le Hen <jeremie at le-hen.org> writes:
> Dag-Erling Smørgrav <des at des.no> writes:
> > They both suck, for different reasons.  In theory, ptrace sucks less
> > than proc, but it lacks some of proc's functionality, and fixing that
> > is very hard.
> Would you take a little time to tell what ptrace lacks and possibly
> why it is so hard, please ?

The way ptrace works, you set debugging conditions using the ptrace(2)
syscall and then use waitpid(2) and friends to wait for them to occur.
For this to work, the traced process must be reparented to the
debugger.  If the traced process's real parent is waiting for its
child, it will become very confused when waitpid(2) returns -1 because
the child has vanished into thin air.  For precisely the same reason,
you can't follow forks with ptrace().

The only way I can see to solve this without modifying the ptrace API
is to introduce a separate process hierarchy for traced processes.
This is hard to do because you basically have to rewrite kern_wait()
from scratch.

The best solution would be to design a new debugging API from scratch.
This is far from trivial, however, and should be done by (or in close
cooperation with) someone intimately familiar with gdb(1) and similar
tools.

DES
-- 
Dag-Erling Smørgrav - des at des.no