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Re: linux-next: add utrace tree

From:  Tom Tromey <tromey-AT-redhat.com>
To:  Linus Torvalds <torvalds-AT-linux-foundation.org>
Subject:  Re: linux-next: add utrace tree
Date:  Mon, 25 Jan 2010 14:05:54 -0700
Message-ID:  <m33a1tnbd9.fsf@fleche.redhat.com>
Cc:  Stephen Rothwell <sfr-AT-canb.auug.org.au>, Kyle Moffett <kyle-AT-moffetthome.net>, Peter Zijlstra <a.p.zijlstra-AT-chello.nl>, Peter Zijlstra <peterz-AT-infradead.org>, Fr??d??ric Weisbecker <fweisbec-AT-gmail.com>, Oleg Nesterov <oleg-AT-redhat.com>, Steven Rostedt <rostedt-AT-goodmis.org>, LKML <linux-kernel-AT-vger.kernel.org>, Arnaldo Carvalho de Melo <acme-AT-redhat.com>, "Frank Ch. Eigler" <fche-AT-redhat.com>, linux-next-AT-vger.kernel.org, "H. Peter Anvin" <hpa-AT-zytor.com>, utrace-devel-AT-redhat.com, Thomas Gleixner <tglx-AT-linutronix.de>
Archive-link:  Article

>>>>> "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




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