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Re: linux-next: add utrace tree

From:  Tom Tromey <>
To:  Linus Torvalds <>
Subject:  Re: linux-next: add utrace tree
Date:  Mon, 25 Jan 2010 14:05:54 -0700
Message-ID:  <>
Cc:  Stephen Rothwell <>, Kyle Moffett <>, Peter Zijlstra <>, Peter Zijlstra <>, Fr??d??ric Weisbecker <>, Oleg Nesterov <>, Steven Rostedt <>, LKML <>, Arnaldo Carvalho de Melo <>, "Frank Ch. Eigler" <>,, "H. Peter Anvin" <>,, Thomas Gleixner <>
Archive-link:  Article

>>>>> "Linus" == Linus Torvalds <> 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.


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