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

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Date:	Fri, 06 Jan 2012 12:42:22 -0800
From:	David Daney <ddaney.cavm@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	linux-kernel@...r.kernel.org, David Daney <david.daney@...ium.com>
Subject: Re: [PATCH] recordmcount: Fix handling of elf64 big-endian objects.

On 12/19/2011 07:09 PM, Steven Rostedt wrote:
> 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.
>

Hi Steven,

Any more feedback on this patch?  Should I look for it to appear in 3.3?

Thanks,
David Daney

> 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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