linux-kernel - Re: [PATCH] ftrace/x86: Fix missing ops arg on static function tracing

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Date:	Tue, 17 Nov 2015 08:44:40 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ftrace/x86: Fix missing ops arg on static function
 tracing

Hi Steve,

On Mon, Nov 16, 2015 at 10:54:53AM -0500, Steven Rostedt wrote:
> On Sat, 14 Nov 2015 18:32:28 +0900
> Namhyung Kim <namhyung@...nel.org> wrote:
> 
> > The commit f1ab00af816e ("ftrace/x86: Get rid of ftrace_caller_setup")
> > moved code that loads ftrace_ops into 3rd parameter but it missed to do
> > for static tracing.
> > 
> > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> > ---
> >  arch/x86/kernel/mcount_64.S | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/arch/x86/kernel/mcount_64.S b/arch/x86/kernel/mcount_64.S
> > index 94ea120fa21f..6c1ccf9e5427 100644
> > --- a/arch/x86/kernel/mcount_64.S
> > +++ b/arch/x86/kernel/mcount_64.S
> > @@ -278,6 +278,9 @@ trace:
> >  	/* save_mcount_regs fills in first two parameters */
> >  	save_mcount_regs
> >  
> > +	/* Load the ftrace_ops into the 3rd parameter */
> > +	movq function_trace_op(%rip), %rdx
> > +
> >  	call   *ftrace_trace_function
> 
> This isn't needed, nor will the parameter be used if added. A comment
> should probably be added here instead.
> 
> /*
>  * When DYNAMIC_FTRACE is not defined, ARCH_SUPPORTS_FTRACE_OPS is not
>  * set (see include/asm/ftrace.h). Only the ip and parent ip are used
>  * and the list function is called when function tracing is enabled.
>  */

Ah, ok.  

I sent this patch during reading update_ftrace_function().  I was
wondering why function_trace_op is set but not passed to the trace
function.  It seems that the ops is not needed for x86 but s390 still
needs it regardless of DYNAMIC_FTRACE.

I'll send a patch with the above comment.

Thanks,
Namhyung

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