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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: Wed, 22 Apr 2015 06:59:13 +0300

В Tue, 21 Apr 2015 18:29:51 -0400
David Shaw <address@hidden> пишет:

> Hello,
> I'm having a problem booting a compressed ISO image using memdisk via grub2 
> (version 2.02, from CentOS 7).  The entry in my grub.cfg looks like:
> menuentry 'boot ISO image' {
>    linux16 /memdisk iso
>    initrd16 /my-image.iso.gz
>  }
> When selected, this starts to boot and then fails with:
>   Ramdisk at 0x37979000, length 0x0033b298
>   gzip image: decompressed addr 0x7f7f7000, len 0x00008f58: failed
>   Decompression error: output buffer overrun
> FWIW, my-image.iso.gz is 3388055

That matches length 0x0033b298 (it is one byte more due to 4 bytes
alignment). So it looks like grub at least passes the right size.

> bytes long compressed, and 9394176 bytes long uncompressed.  The box
 in question has 8GiB of RAM.
> Note that the uncompressed size of the iso in hex comes out to 8F5800.  The 
> length given in the error message is 8F58 - that is, exactly 256 times too 
> small.  That seems suspicious.
> 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

> 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?

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