Patchwork powerpc/ftrace: fix constraint to be early clobber

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Submitter Steven Rostedt
Date May 15, 2009, 2:33 p.m.
Message ID <alpine.DEB.2.00.0905141236420.30591@gandalf.stny.rr.com>
Download mbox | patch
Permalink /patch/27261/
State Accepted
Delegated to: Benjamin Herrenschmidt
Headers show

Comments

Steven Rostedt - May 15, 2009, 2:33 p.m.
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@goodmis.org>
Benjamin Herrenschmidt - May 15, 2009, 10:27 p.m.
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@goodmis.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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Patch

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"
 	);