linux-kernel - Re: [bisected] 2.6.29-rc1 Firefox crashing on page load

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Date:	Tue, 20 Jan 2009 18:39:11 -0800
From:	Justin Madru <jdm64@...ab.com>
To:	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
CC:	"Justin P. Mattock" <justinmattock@...il.com>,
	Jesper Juhl <jj@...osbits.net>,
	lkml <linux-kernel@...r.kernel.org>,
	John Stoffel <john@...ffel.org>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [bisected] 2.6.29-rc1 Firefox crashing on page load

Hiroshi Shimamoto wrote:
> Justin Madru wrote:
>   
>> Hiroshi Shimamoto wrote:
>>     
>>> Justin Madru wrote:
>>>   
>>>       
>>>> Hiroshi Shimamoto wrote:
>>>>     
>>>>         
>>>>> Justin Madru wrote:
>>>>>       
>>>>>           
>>>>>> Ok, finally bisected the bug, but the commit isn't related to networking!
>>>>>> I did: git revert 4217458dafaa57d8e26a46f5d05ab8c53cf64191
>>>>>> on current git and that fixed the bug.
>>>>>>
>>>>>> By the way, how do I undo my git revert, so I'm back to a pristine tree?
>>>>>> I want to drop my changes - the revert.
>>>>>> Also how do I find the commit that merged/pulled in this commit?
>>>>>>
>>>>>> commit 4217458dafaa57d8e26a46f5d05ab8c53cf64191
>>>>>> Author: Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
>>>>>> Date: Fri Dec 5 17:17:09 2008 -0800
>>>>>>
>>>>>> x86: signal: change type of paramter for sys_rt_sigreturn()
>>>>>>
>>>>>> Impact: cleanup on 32-bit
>>>>>>
>>>>>> Peter pointed this parameter can be changed.
>>>>>>
>>>>>> Signed-off-by: Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
>>>>>> Signed-off-by: Ingo Molnar <mingo@...e.hu>
>>>>>>         
>>>>>>             
>>>>> Hi,
>>>>> thanks for reporting.
>>>>>
>>>>> I'm not sure why this commit affects.
>>>>> Can you check vmlinux? size, objdump, etc.
>>>>> On my environment, the generated code looks same.
>>>>>
>>>>> Thanks,
>>>>> Hiroshi
>>>>>
>>>>>       
>>>>>           
>>>> I tried to do an objdump but it gave an error. How am I suppose to do an 
>>>> objdump?
>>>>
>>>> $ objdump -x /boot/vmlinuz-2.6.29-rc2-git
>>>> objdump: /boot/vmlinuz-2.6.29-rc2-git: File format not recognized
>>>> $ readelf -a /boot/vmlinuz-2.6.29-rc2-git
>>>> readelf: Error: Unable to seek to 0xc031f2eb for section headers
>>>> readelf: Error: Not an ELF file - it has the wrong magic bytes at the start
>>>> $ ls -la /boot/vmlinuz-2.6.29-rc2-git
>>>> -rw-r--r-- 1 root root 2286480 2009-01-19 18:44 /boot/vmlinuz-2.6.29-rc2-git
>>>>     
>>>>         
>>> not vmlinuz, vmlinux.
>>> vmlinuz is a compressed kernel, it is not ELF file.
>>> Usually vmlinux is generated in top of source directory.
>>> I can see disassembled image with objdump -d vmlinux.
>>>
>>> Thanks,
>>> Hiroshi
>>>
>>>   
>>>       
>> Sorry, didn't know. I tried objdump -d vmlinux, but the resulting file 
>> is ~50MB!
>> Is there a smaller section you're interested in, because that would be 
>> hard to send.
>> Or am I doing it wrong again?
>>     
>
> that's OK. No need to send the disassembled result.
> You can diff disassembled file.
> I guess your GCC generates different code when the patch is reverted.
>
> Thanks,
> Hiroshi
>
>   
Ok, I tried, I really did. But no mater what I did the diff was even bigger
if not the same size as the original dump! I even tried to cut out the 
first two fields with
    cut -f3- dump-revert > dump-revert2
but that wouldn't shrink the diff size (100,000+ lines).

Does gcc output fluctuate this wildly with such little change?
Is there a config option that allows gcc to randomize the output?
I recompiled just to make sure, and even two recompiles of the same 
source (no revert)
resulted in a different sha1 hash (didn't test the objdump diff).
The only thing I can think of is that I compile with -O3 instead of -O2.

I'm sorry, but unless you have any suggestions I've decided to just upload
the vmlinux files to my server (<40KB up speed) 
http://jdserver.homelinux.org/bugreports/002/
and rapidshare
http://rapidshare.com/files/186890846/vmlinux.tar.bz2.html
http://rapidshare.com/files/186890848/data-norevert.tar.bz2.html
http://rapidshare.com/files/186890849/data-revert.tar.bz2.html

By the way Ingo has already added the revert to tip/master
http://git.kernel.org/?p=linux/kernel/git/tip/linux-2.6-tip.git;a=commit;h=1d03950243904c89b8854c10516932b029c2a8fa

Justin Madru
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