[PATCH] ftrace/x86: Fix missing ops arg on static function tracing

[PATCH] ftrace/x86: Fix missing ops arg on static function tracing

[Namhyung Kim]

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@kernel.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
 
 	restore_mcount_regs
-- 
2.6.2

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

[Steven Rostedt]

On Sat, 14 Nov 2015 18:32:28 +0900
Namhyung Kim <namhyung@kernel.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@kernel.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.
 */

-- Steve

>  
>  	restore_mcount_regs

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

[Steven Rostedt]

On Mon, 16 Nov 2015 10:54:53 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:
 
> /*
>  * 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.
>  */
> 

Namhyung, if you want to send a patch that adds this comment feel free
to do so.

-- Steve

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

[Steven Rostedt]

On Mon, 16 Nov 2015 10:54:53 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> 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

Probably should also add "and include/linux/ftrace.h" as that's where
the ARCH_SUPPORTS_FTRACE_OPS is described.

-- Steve

>  * and the list function is called when function tracing is enabled.
>  */
> 

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

[Namhyung Kim]

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@kernel.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@kernel.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