linux-kernel - Re: [PATCH] ftrace/x86: Fix function graph tracer reset path

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Date:	Mon, 16 May 2016 23:24:53 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Masami Hiramatsu <mhiramat@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
	Borislav Petkov <bp@...e.de>, "H.J. Lu" <hjl.tools@...il.com>
Subject: Re: [PATCH] ftrace/x86: Fix function graph tracer reset path

Hi Steve,

On Mon, May 16, 2016 at 09:58:33AM -0400, Steven Rostedt wrote:
> 
> Nice work Masami!
> 
> On Mon, 16 May 2016 21:32:50 +0900
> Namhyung Kim <namhyung@...nel.org> wrote:
> 
>     
> > >     -/* This is global to keep gas from relaxing the jumps */
> > >     -ENTRY(early_idt_handler)
> > >     +/* This is weak to keep gas from relaxing the jumps */
> > >     +WEAK(early_idt_handler)
> > >      	cld
> 
> > So IIUC, this -mshared option disables the optimization on branch
> > instructions and generates slightly bigger code.  Not sure how much
> > affected by this though.
> > 
> > Steve, do you think it's better to use this option?
> 
> Can we solve this by doing the same thing it did for the kernel?

Yes, it fixes my problem.

Thanks,
Namhyung


> 
> diff --git a/arch/x86/kernel/mcount_64.S b/arch/x86/kernel/mcount_64.S
> index ed48a9f465f8..e13a695c3084 100644
> --- a/arch/x86/kernel/mcount_64.S
> +++ b/arch/x86/kernel/mcount_64.S
> @@ -182,7 +182,8 @@ GLOBAL(ftrace_graph_call)
>  	jmp ftrace_stub
>  #endif
>  
> -GLOBAL(ftrace_stub)
> +/* This is weak to keep gas from relaxing the jumps */
> +WEAK(ftrace_stub)
>  	retq
>  END(ftrace_caller)
>