linux-kernel - Re: [PATCH 06/10] ARM: ftrace: add Thumb-2 support

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Message-ID: <20100315183258.GA2141@debian>
Date:	Tue, 16 Mar 2010 00:02:58 +0530
From:	Rabin Vincent <rabin@....in>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Abhishek Sagar <sagar.abhishek@...il.com>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Subject: Re: [PATCH 06/10] ARM: ftrace: add Thumb-2 support

On Sun, Mar 14, 2010 at 10:30:15PM +0000, Catalin Marinas wrote:
> On Sat, 2010-03-13 at 06:49 +0000, Rabin Vincent wrote:
> >  - The problem with the "mov lr, pc", is that it does not set the lsb when
> >    storing the pc in lr.  The called function returns with "bx lr", and the
> >    mode changes to ARM.  The blx is to avoid this.
> 
> I'm not familiar with ftrace but why does the called function returns
> using "bx lr". Is this generated by the compiler? I had the impression
> that if we don't enable interworking, we wouldn't get this instruction
> (but haven't tried this yet).

There's nothing special about the called function: it's just a regular C
function.  GCC uses "bx lr" for the return.

Rabin
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