linux-kernel - Re: linux-next: add utrace tree

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Date:	Mon, 25 Jan 2010 14:05:54 -0700
From:	Tom Tromey <tromey@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Kyle Moffett <kyle@...fetthome.net>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Peter Zijlstra <peterz@...radead.org>,
	Fr??d??ric Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	linux-next@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	utrace-devel@...hat.com, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: linux-next: add utrace tree

>>>>> "Linus" == Linus Torvalds <torvalds@...ux-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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