Re: i386/pc/chainloader.c fails with syntax like chainloader (hd1, msdos1)+1

["Vladimir 'φ-coder/phcoder' Serbinenko" <phcoder@gmail.com>]

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On 21.06.2013 11:23, Michael Chang wrote:
> Hi,
> 
> The i386/pc/chainloader.c hangs when attempting to chainload other
> disk's boot sector (or mbr) with a syntax like this. Say if current
> environment setting root=hd0,msdos2.
> 
>   $ chainloader (hd1,msdos1)+1
> 
> However doing it this way always works.
> 
>   $ set root=hd1,msdos1
>   $ chainloader +1
> 
> I suppose the first syntax is valid as it should override $root [1]
> thus two cases should have identical result. But looking into the
> chainloader source it seems that the $root is always used to obtain
> the boot drive number and partition table. So there's a discrepancy if
> root is not set to the chainloader device which is explicitly
> specified in file.
No, the behaviour you see is intended consider someone copying
bootsector from (hd1,1) to (hd0,2)/boot.bin. It can still be booted with:
root=hd1,1
chainloader (hd0,2)/boot.bin
The disk passed in %dl and where the sector is loaded from isn't
necessarily the same.
> 
> The attached file fixes the problem for me, I'd like to contribute if
> you think this is a problem or how to improve the patch.
> 
> [1] http://www.gnu.org/software/grub/manual/grub.html#root
> [2] http://www.gnu.org/software/grub/manual/grub.html#chainloader
> 
> Thanks,
> Michael
> 
> 
> 
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> 



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