Re: How to make a GRUB image file that can be chainloaded and will not read the MBR gap?

[Basin Ilya]

Hi Andrei.

Thanks, that did the trick. I thought lnxboot.img was only for LILO.


30.06.2016 20:20, Andrei Borzenkov пишет:
> I answer on help because it is surely not grub-devel material.
> 
> 30.06.2016 16:34, Basin Ilya пишет:
>> Hi.
>>
>> I want to make my grub image file independent from the data in the MBR
>> gap, i.e. I want to embed the generated core.img into my custom image file.
>>
>> I have some questions:
>>
>> - Does the grub2 command "chainloader /foo.img" load the whole file or
>> just the 1st 512 bytes?
>>
> 
> Just 512 bytes.
> 
>> - Does a BOOTSECTOR entry in Windows boot manager load the whole file or
>> just the 1st 512 bytes?
>>
> 
> IIRC it loads full file.
> 
>> If the answer to both questions is "yes", then a custom image can be
>> made that will include core.img and a very simple boot sector, that will
>> assume that core.img is already loaded. To my knowledge, neither of the
>> images that ship with grub2 does that.
>>
> 
> That is what lnxboot.img is for. It makes core.img loadable both by
> Windows boot manager as well as grub2 "linux16" command.
> 
>> What preparations should the custom boot sector do? At what offset
>> should core.img be loaded and jumped to?
>>
> 
> cat lnxboot.img core.img > your-custom-boot.img
> 
> If it turns out popular enough, it is trivial to add to grub-mkimage.
> 
> P.S. Theoretically you should be able to do
> 
> linux16 lnxboot.img
> initrd16 core.img
> boot
> 
> Except it does not work ...
>