linux-kernel - Re: [PATCH] scripts: add extract-vmlinux

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Date:	Thu, 11 Aug 2011 15:33:51 +0200
From:	Michal Marek <mmarek@...e.cz>
To:	Corentin Chary <corentin.chary@...il.com>
Cc:	Paul Bolle <pebolle@...cali.nl>, linux-kernel@...r.kernel.org,
	Dick Streefland <dick@...eefland.net>,
	WANG Cong <xiyou.wangcong@...il.com>
Subject: Re: [PATCH] scripts: add extract-vmlinux

On 11.8.2011 15:08, Corentin Chary wrote:
> On Thu, Aug 11, 2011 at 1:28 PM, Paul Bolle <pebolle@...cali.nl> wrote:
>> On Thu, 2011-08-11 at 10:53 +0200, Corentin Chary wrote:
>>> +try_decompress()
>>> +{
>>> +     for     pos in `tr "$1\n$2" "\n$2=" < "$img" | grep -abo "^$2"`
>>> +     do
>>> +             pos=${pos%%:*}
>>> +             tail -c+$pos "$img" | $3 > $tmp 2> /dev/null
>>
>> Perhaps a few comments on the above lines would be nice. Without those
>> comments I must guess you're finding compressed data somewhere in the
>> input file. It also seems you're looping through the entire input file.
>> Or are (sequences of) commands like the above considered obvious?
> 
> It's copied from extract-ikconfig, there was no comment in it, so I
> assumed it's obvious.
> Basically it uses brute force (tm) to find well known headers and try
> to decompress from here.

And explanation of the "tr" trick would not hurt though. It replaces the
binary magic with an ascii sequence on a new line (for older grep
versions to get it right) and tries all occurrences of that sequence, am
I right? But I wouldn't call it "obvious" :).


>>> +# That didn't work, so retry after decompression.
>>> +try_decompress '\037\213\010' xy    gunzip
>>> +try_decompress '\3757zXZ\000' abcde unxz
>>> +try_decompress 'BZh'          xy    bunzip2
>>> +try_decompress '\135\0\0\0'   xxx   unlzma
>>> +try_decompress '\211\114\132' xy    'lzop -d'
>>
>> Perhaps you could first test whether these commands are available before
>> running try_decompress() with them?
> 
> Same as before, if it's ok for extract-ikconfig not to check the
> command, then it's ok for me.
> If it's not, then we should patch both.

Also, if you have lzma to build a lzma-compressed kernel, then you very
likely also have unlzma.

Michal
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