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

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Message-ID: <20100123115149.GB7828@redhat.com>
Date:	Sat, 23 Jan 2010 06:51:49 -0500
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Kyle Moffett <kyle@...fetthome.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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

Hi -

On Sat, Jan 23, 2010 at 11:01:21AM +0000, Alan Cox wrote:
> [...]
> What I don't understand is why [libgdb?] doesn't solve 99% of your problem.
> ptrace is not perfect but most of the real ptrace limitations actually
> come about because either the CPU can't do something or because the
> supporting logic would be too expensive - things like having extra
> private debugger pages.

At least one reason is that ptrace is single-usage-only, so for
example you cannot concurrently debug & strace the same program.
OTOH, utrace is designed to permit clean nesting/sharing semantics for
concurrent debugger-type tools operating on the same processes.

- FChE
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