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

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Message-ID: <alpine.LFD.2.00.1001261535510.17519@localhost.localdomain>
Date:	Tue, 26 Jan 2010 15:37:49 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Tom Tromey <tromey@...hat.com>
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



On Tue, 26 Jan 2010, Tom Tromey wrote:
> 
> In non-stop mode (where you can stop one thread but leave the others
> running), gdb wants to have the breakpoints always inserted.  So,
> something must emulate the displaced instruction.

I'm almost totally uninterested in breakpoints that actually re-write 
instructions. It's impossible to do that efficiently and well, especially 
in threaded environments.

So if you do instruction rewriting, I can only say "that's your problem".

But using the hardware breakpoints should automatically DTRT, both wrt 
threads _and_ wrt restarting. Sure, there's onyl a limited number of them, 
so if somebody wants more than that they are kind of screwed, but that's 
just how life is.

		Linus
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