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Subject: Re: [PATCH -v5] MIPS: tracing: Optimize the implementation
From:   Wu Zhangjin <wuzhangjin@gmail.com>
Reply-To: wuzhangjin@gmail.com
To:     Ralf Baechle <ralf@linux-mips.org>
Cc:     linux-mips@linux-mips.org, Steven Rostedt <rostedt@goodmis.org>
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References: <1271537514-19584-1-git-send-email-wuzhangjin@gmail.com>
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Organization: DSLab, Lanzhou University, China
Date:   Mon, 19 Apr 2010 17:36:08 +0800
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On Sun, 2010-04-18 at 04:51 +0800, Wu Zhangjin wrote:
[...]
> diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S
[...]
>  
> @@ -45,8 +46,6 @@
>  	PTR_L	a5, PT_R9(sp)
>  	PTR_L	a6, PT_R10(sp)
>  	PTR_L	a7, PT_R11(sp)
> -#endif
> -#ifdef CONFIG_64BIT
>  	PTR_ADDIU	sp, PT_SIZE
>  #else
>  	PTR_ADDIU	sp, (PT_SIZE + 8)
> @@ -71,7 +70,7 @@ _mcount:
>  
>  	MCOUNT_SAVE_REGS
>  #ifdef KBUILD_MCOUNT_RA_ADDRESS
> -	PTR_S	t0, PT_R12(sp)	/* t0 saved the location of the return address(at) by -mmcount-ra-address */
> +	PTR_S	$12, PT_R12(sp)	/* $12 saved the location of the return address(at) */
>  #endif
>  
>  	move	a0, ra		/* arg1: next ip, selfaddr */
> @@ -137,25 +136,22 @@ NESTED(ftrace_graph_caller, PT_SIZE, ra)
>  #ifdef CONFIG_DYNAMIC_FTRACE
>  	PTR_L	a1, PT_R31(sp)	/* load the original ra from the stack */
>  #ifdef KBUILD_MCOUNT_RA_ADDRESS
> -	PTR_L	t0, PT_R12(sp)	/* load the original t0 from the stack */
> +	PTR_L	a0, PT_R12(sp)	/* arg1: the location of the return address */
>  #endif
> -#else
> +#else /* ! CONFIG_DYNAMIC_FTRACE */
>  	MCOUNT_SAVE_REGS
>  	move	a1, ra		/* arg2: next ip, selfaddr */
>  #endif
>  
>  #ifdef KBUILD_MCOUNT_RA_ADDRESS
> -	bnez	t0, 1f		/* non-leaf func: t0 saved the location of the return address */
> +	bnez	a0, 1f		/* non-leaf func: get the location of the return address from saved $12 */
>  	 nop
> -	PTR_LA	t0, PT_R1(sp)	/* leaf func: get the location of at(old ra) from our own stack */
> -1:	move	a0, t0		/* arg1: the location of the return address */
> -#else
> -	PTR_LA	a0, PT_R1(sp)	/* arg1: &AT -> a0 */
>  #endif
> -	jal	prepare_ftrace_return

The above change has broken the static function graph tracer with
-mmcount-ra-address for it did not consider the argument 1 for static
function graph tracer, a new revision of this patch will be sent out as
"MIPS: tracing: adds misc cleanups and fixups".

Regards,
	Wu Zhangjin