linux-kernel - Re: [RFC][PATCH 03/13 v2] ftrace: Return pt

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Date:	Fri, 15 Jun 2012 12:02:58 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	yrl.pp-manager.tt@...achi.com
Subject: Re: [RFC][PATCH 03/13 v2] ftrace: Return pt_regs to function trace
 callback

(2012/06/13 7:43), Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@...hat.com>
> 
> Return as the 4th paramater to the function tracer callback the pt_regs.
> 
> Currently x86_64 just passes NULL as the regs arguement. Later patches
> that implement regs passing will require having the ftrace_ops set the
> SAVE_REGS flag, which will tell the arch to take the time to pass a
> full set of pt_regs to the ftrace_ops callback function. If the arch
> does not support it then it should pass NULL.

Hmm, I think the x86-64 part of this patch would be better to be separated
with x86-64 part of [5/13], so that I can easily review the change...
Another reason is that this patch doesn't define ARCH_SUPPORTS_FTRACE_SAVE_REGS
on x86_64 too...


> A ftrace_ops call back can either check if the macro ARCH_SUPPORTS_FTRACE_SAVE_REGS
> is defined, or it can check if regs is NULL. As it will be NULL if
> it is not supported by the arch even if the SAVE_REGS flag is set.
> 
> If an arch can pass full regs, then it should define:
>  ARCH_SUPPORTS_FTRACE_SAVE_REGS to 1
> 
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
[...]
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index 2b4f94c..83d8ae0 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -80,7 +80,11 @@ ENTRY(ftrace_caller)
>  	MCOUNT_SAVE_FRAME
>  
>  	leaq function_trace_op, %rdx
> -	movq 0x38(%rsp), %rdi
> +
> +	/* regs go into 4th parameter (but make it NULL) */
> +	movq $0, %rcx

There is no ARCH_SUPPORTS_FTRACE_SAVE_REGS, so I think you
don't need to clear rcx at least this time.

Another generic ftrace part of this patch is good to me :)

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

Thank you,


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
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