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Re: Using memdisk with grub2 and a compressed ISO

From: David Shaw
Subject: Re: Using memdisk with grub2 and a compressed ISO
Date: Wed, 22 Apr 2015 15:14:43 -0400

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.
>> Any suggestions on where to look next?
> Could you provide link to images you are using so I could try to
> reproduce it?

Sure, the iso is at:

Thanks for looking at this,


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