linux-kernel - Re: [PATCH] tracing: recordmcount.pl: Fix $mcount

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Date:	Fri, 09 Jul 2010 20:26:02 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	David Daney <ddaney@...iumnetworks.com>
Cc:	linux-kernel@...r.kernel.org, linux-mips@...ux-mips.org,
	Li Hong <lihong.hi@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Matt Fleming <matt@...sole-pimps.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Wu Zhangjin <wuzhangjin@...il.com>
Subject: Re: [PATCH] tracing: recordmcount.pl: Fix $mcount_regex for MIPS.

On Fri, 2010-07-09 at 14:52 -0700, David Daney wrote:
> I found this issue in a locally patched 2.6.32.x, current kernels have
> moved the offending code to an __init function which is skipped by
> recordmcount.pl, so the bug is not currently being exercised.
> However, I think the patch is still a good idea, to avoid future
> problems if _mcount were to ever have its address taken in normal
> code.
> 
> This is what I originally saw:
> 
>     Although arch/mips/kernel/ftrace.c is built without -pg, and thus
>     contains no calls to _mcount, it does use the address of _mcount
>     in ftrace_make_nop().  This was causing relocations to be emitted
>     for _mcount which recordmcount.pl erronously took to be _mcount
>     call sites.  The result was that the text of ftrace_make_nop()
>     would be patched with garbage leading to a system crash.
> 
> In non-module code, all _mcount call sites will have R_MIPS_26
> relocations, so we restrict $mcount_regex to only match on these.
> 

I'd like to get an Acked-by from Ralf and Wu before pulling this.

Thanks,

-- Steve

> Signed-off-by: David Daney <ddaney@...iumnetworks.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Li Hong <lihong.hi@...il.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Matt Fleming <matt@...sole-pimps.org>
> Cc: Ralf Baechle <ralf@...ux-mips.org>
> ---
>  scripts/recordmcount.pl |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
> index f3c9c0a..0171060 100755
> --- a/scripts/recordmcount.pl
> +++ b/scripts/recordmcount.pl
> @@ -326,7 +326,7 @@ if ($arch eq "x86_64") {
>      #                    14: R_MIPS_NONE *ABS*
>      #	 18:   00020021        nop
>      if ($is_module eq "0") {
> -	    $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
> +	    $mcount_regex = "^\\s*([0-9a-fA-F]+): R_MIPS_26\\s+_mcount\$";
>      } else {
>  	    $mcount_regex = "^\\s*([0-9a-fA-F]+): R_MIPS_HI16\\s+_mcount\$";
>      }


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