Re: linux-next: add utrace tree

[Tom Tromey <tromey@redhat.com>]

>>>>> "Linus" == Linus Torvalds <torvalds@linux-foundation.org> writes:

Linus> No. There is absolutely _no_ reason to believe that gdb et al would ever 
Linus> delete the ptrace interfaces anyway. 

Yes, in GDB we approximately never delete anything.

Nevertheless, if the Linux kernel were to present a new user-space API,
and if it had an advantage over ptrace, then we would port GDB to use
it.  There are other platforms where, IIRC, we now use some /proc thing
instead of ptrace.

There are definitely things we would like from such an API.  Here's a
few I can think of immediately, there are probably others.

* Use an fd, not SIGCHLD+wait, to report inferior state changes to gdb.
  Internally we're already using a self-pipe to integrate this into
  gdb's main loop.  Relatedly, don't mess with the inferior's parentage.

* Support "displaced stepping" in the kernel; I think this would improve
  performance when debugging in non-stop mode.

* Support some kind of breakpoint expression in the kernel; this would
  improve performance of conditional breakpoints.  Perhaps the existing
  gdb agent expressions could be used.

Tom