linux-kernel - Re: [PATCH] powerpc/ftrace: fix constraint to be early clobber

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Message-Id: <1242426438.9691.5.camel@pasglop>
Date:	Sat, 16 May 2009 08:27:18 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, linuxppc-dev@...abs.org,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] powerpc/ftrace: fix constraint to be early clobber

On Fri, 2009-05-15 at 10:33 -0400, Steven Rostedt wrote:
> After upgrading my distcc boxes from gcc 4.2.2 to 4.4.0, the function 
> graph tracer broke. This was discovered on my x86 boxes.
> 
> The issue is that gcc used the same register for an output as it did for 
> an input in an asm statement. I first thought this was a bug in gcc and 
> reported it. I was notified that gcc was correct and that the output had 
> to be flagged as an "early clobber".
> 
> I noticed that powerpc had the same issue and this patch fixes it.
> 
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

Ack. You merge this or I do ?

Cheers,
Ben.

> diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
> index 70e2a73..68fd74e 100644
> --- a/arch/powerpc/kernel/ftrace.c
> +++ b/arch/powerpc/kernel/ftrace.c
> @@ -594,7 +594,7 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
>  			PPC_LONG "2b,4b\n"
>  		".previous"
>  
> -		: [old] "=r" (old), [faulted] "=r" (faulted)
> +		: [old] "=&r" (old), [faulted] "=r" (faulted)
>  		: [parent] "r" (parent), [return_hooker] "r" (return_hooker)
>  		: "memory"
>  	);
> 
> --
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