linux-kernel - Re: [PATCH] recordmcount: Fix handling of elf64 big-endian objects.

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Message-ID: <1324350542.5916.48.camel@gandalf.stny.rr.com>
Date:	Mon, 19 Dec 2011 22:09:02 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	David Daney <ddaney.cavm@...il.com>
Cc:	linux-kernel@...r.kernel.org, David Daney <david.daney@...ium.com>
Subject: Re: [PATCH] recordmcount: Fix handling of elf64 big-endian objects.

On Mon, 2011-12-19 at 17:42 -0800, David Daney wrote:
> From: David Daney <david.daney@...ium.com>
> 
> In ELF64, the sh_flags field is 64-bits wide.  recordmcount was
> erroneously treating it as a 32-bit wide field.  For little endian
> objects this works because the flags of interest (SHF_EXECINSTR)
> reside in the lower 32 bits of the word, and you get the same result
> with either a 32-bit or 64-bit read.  Big endian objects on the
> other hand do not work at all with this error.
> 
> The fix:  Correctly treat sh_flags as 64-bits wide in elf64 objects.
> 
> The symptom I observed was that my
> __start_mcount_loc..__stop_mcount_loc was empty even though ftrace
> function tracing was enabled.
> 

OUCH!

This looks like something that needs to go to stable. Let me play with
this on my PPC64 tomorrow.

Thanks!

-- Steve

> Signed-off-by: David Daney <david.daney@...ium.com>
> ---
>  scripts/recordmcount.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h
> index f40a6af6..54e35c1 100644
> --- a/scripts/recordmcount.h
> +++ b/scripts/recordmcount.h
> @@ -462,7 +462,7 @@ __has_rel_mcount(Elf_Shdr const *const relhdr,  /* is SHT_REL or SHT_RELA */
>  		succeed_file();
>  	}
>  	if (w(txthdr->sh_type) != SHT_PROGBITS ||
> -	    !(w(txthdr->sh_flags) & SHF_EXECINSTR))
> +	    !(_w(txthdr->sh_flags) & SHF_EXECINSTR))
>  		return NULL;
>  	return txtname;
>  }


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