linux-kernel - Re: [PATCH -v6 05/13] tracing: enable HAVE_FUNCTION_TRACE_MCOUNT

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Date:	Mon, 26 Oct 2009 18:41:56 +0300
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Wu Zhangjin <wuzhangjin@...il.com>
Cc:	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>, rostedt@...dmis.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Richard Sandiford <rdsandiford@...glemail.com>,
	Nicholas Mc Guire <der.herr@...r.at>,
	David Daney <ddaney@...iumnetworks.com>,
	Adam Nemet <anemet@...iumnetworks.com>,
	Patrik Kluba <kpajko79@...il.com>
Subject: Re: [PATCH -v6 05/13] tracing: enable HAVE_FUNCTION_TRACE_MCOUNT_TEST
 for MIPS

Hello.

Wu Zhangjin wrote:

> There is an exisiting common ftrace_test_stop_func() in
> kernel/trace/ftrace.c, which is used to check the global variable
> ftrace_trace_stop to determine whether stop the function tracing.

> This patch implepment the MIPS specific one to speedup the procedure.

> Thanks goes to Zhang Le for Cleaning it up.

> Signed-off-by: Wu Zhangjin <wuzhangjin@...il.com>

[...]

> diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S
> index 0c39bc8..5dfaca8 100644
> --- a/arch/mips/kernel/mcount.S
> +++ b/arch/mips/kernel/mcount.S
> @@ -64,6 +64,10 @@
>  	.endm
>  
>  NESTED(_mcount, PT_SIZE, ra)
> +	lw	t0, function_trace_stop
> +	bnez	t0, ftrace_stub
> +	nop

1) unless .set noreorder is specified in this file, explicit nop is not needed;

2) delay slot instruction is usually denoted by adding extra space on its 
left, like this:

	bnez	t0, ftrace_stub
	 nop

WBR, Sergei
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