XZ embedded bug unpacking linux-3.8.tar.xz

Roy roytam at gmail.com
Fri Mar 1 00:30:59 UTC 2013


In Fri, 01 Mar 2013 06:20:16 +0800, Antonio Diaz Diaz  
<ant_diaz at teleline.es> wrote:
> Denys Vlasenko wrote:
>>> Why?. *.lzma are deprecated some time ago
>>  Because someone submitted the code:
>
> I also submitted the code[1]. :-)
>
> [1] http://lists.busybox.net/pipermail/busybox/2012-December/078750.html
>
>
>> In fact, it is surprisingly small:
>>  archival/libarchive:
>>    text    data     bss     dec     hex filename
>>    2827       0       0    2827     b0b decompress_unlzma.o
>>    7277       0       0    7277    1c6d decompress_unxz.o
>>    2743       0       0    2743     ab7 decompress_bunzip2.o
>>    5270       0       0    5270    1496 decompress_gunzip.o
>
> Just the same size as lunzip minus the header and integrity checkings:
>
> text+data text+rodata    rwdata       bss filename
>       2928        2928         0         0  
> archival/libarchive/decompress_lunzip.o
>

I wonder, why not adding .lzma support in lunzip(like what pdlzip does)  
for deprecating decompress_unlzma?

>
>> So basically, lzip lost the race wrt adoption. xz is used more widely.
>> Kernel tarballs are .xz, not .lz.
>
> It depends on where you get your kernels from:
>
> http://linux-libre.fsfla.org/pub/linux-libre/releases/3.8-gnu/
>
> BTW, xz files are a bit smaller than lz files in the above directory,  
> but you need twice the memory to decompress them. Of course lzip can  
> achieve the same (or better) compresion if you add "-s 64MiB" to the  
> command line.
>
>
>> What I'm saying is that bbox project would like to have is (ideally)
>> _one_ LZMA decoder. Unpacking the compressed stream from two formats
>> isn't a terribly difficult thing.
>
> But xz is not (only) a LZMA encoder, therefore no LZMA decoder will ever  
> be able to decode xz streams.
>

IIRC .xz uses LZMA2 but not LZMA(version 1, which lzma.exe uses)

>
>> But can lzip decompress unxz *stream*?
>
> If we have learned something from this thread is that not even all  
> unxz's can decompress all xz streams. Much less verify their integrity.
>
>
> Regards,
> Antonio.



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