linux-kernel - Re: [PATCH] i386 TIF flags for debug regs and io bitmap in ctxsw (v2)

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Message-ID: <20060725201845.GH19928@frankl.hpl.hp.com>
Date:	Tue, 25 Jul 2006 13:18:45 -0700
From:	Stephane Eranian <eranian@....hp.com>
To:	Chuck Ebbert <76306.1226@...puserve.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...l.org>, Andi Kleen <ak@...e.de>
Subject: Re: [PATCH] i386 TIF flags for debug regs and io bitmap in ctxsw (v2)

Chuck,

On Tue, Jul 25, 2006 at 03:19:49PM -0400, Chuck Ebbert wrote:
> 
> > As for TIF_DEBUG, my patch is not clearing it. I don't think you can
> > have HW breakpoints be inherited from one task to the other.
> 
> Looks like the debug regs get copied on fork and only cleared on exec
> in flush_thread().  So this should be OK.  Please doublecheck.
> 
How is this supposed to work? You can set debug registers via ptrace().
So A is ptracing B and sets up breakpoints in B. Now, if B forks C,
C inherits the breakpoints of B. But what about the ptracing and re-parenting
that is associated with this? If A does not know about C, I wonder how this
could be work and be useful?

> (The new TIF_DEBUG flag went into 2.8.18-rc, in case you didn't notice.)

I did not keep track but thanks or this update. That's great!

-- 
-Stephane
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