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Re: Using memdisk with grub2 and a compressed ISO

From: Andrei Borzenkov
Subject: Re: Using memdisk with grub2 and a compressed ISO
Date: Thu, 23 Apr 2015 12:11:20 +0300

On Wed, Apr 22, 2015 at 10:14 PM, David Shaw <address@hidden> wrote:
> On Apr 21, 2015, at 11:59 PM, Andrei Borzenkov <address@hidden> wrote:
>>> 1) I have tried this with memdisk from syslinux 4.02, 4.05, and 6.03.  Same 
>>> failure each time.
>>> 2) Changing the level of compression (i.e. gzip -1 instead of gzip -9) does 
>>> not make it work.
>>> 3) Doing the same thing with grub1 (version 0.97), but using the same image 
>>> and same version of memdisk, *does* work.
>> Could you show the same messages (load address and size) from grub
>> legacy?
> Sure, here is a brand new test, using the same memdisk (4.02) and same iso 
> image.  Both machines have 4GiB of RAM.  The only difference is grub legacy 
> (0.97) vs grub2 (2.02).
> The iso image is 3388047 bytes gzip compressed and 9394176 bytes uncompressed.
> 0.97 says:
>   Ramdisk at 0x37cb4000, length 0x0033b28f
>   gzip image: decompressed addr 0xbf5fa800, len 0x008f5800: ok
>   (followed by the usual boot messages, etc)
> 2.02 says:
>   Ramdisk at 0x37979000, length 0x0033b290
>   gzip image: decompressed addr 0xbfff7000, len 0x00008f58: failed
>   Decompression error: output buffer overrun
> Note the len from 0.97 is shifted over one byte (exactly 0x100 times larger) 
> compared to the len from 2.02.
>>> 4) Uncompressing the ISO *does* make it work.
>>> 5) Using "zip" instead of "gzip" *does* make it work.
>>> I've mailed with the syslinux / memdisk folks and they suggested coming 
>>> here, as it looked like a grub2 issue.

I see where the problem is but I'm not convinced it is grub issue.
grub behavior is compatible with Linux and works there; as long as
syslinux pretends to be Linux here I expect it to also emulate Linux

Anyway this is topic for grub-devel; you are welcome to raise common
discussion on syslinux and grub-devel lists for it.

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