linux-kernel - Re: [PATCH v2 23/31] arm64: Debugging support

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Message-ID: <20120820090754.GB25864@mudshark.cambridge.arm.com>
Date:	Mon, 20 Aug 2012 10:07:54 +0100
From:	Will Deacon <will.deacon@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Catalin Marinas <Catalin.Marinas@....com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ulrich.weigand@...aro.org" <ulrich.weigand@...aro.org>
Subject: Re: [PATCH v2 23/31] arm64: Debugging support

On Fri, Aug 17, 2012 at 08:06:07AM +0100, Arnd Bergmann wrote:
> Sorry for the dumb question, but why do you even need PTRACE_GET_THREAD_AREA
> for 64 bit tasks? I thought the thread pointer is a GPR, or is this just
> for compat tasks?

The TLS is stored in a co-processor register which is read-only for
userspace. However, it's banked, so accessing the TLS of your child (the guy
you're ptracing) requires a system call.

Will
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