Re: Chainloading an MS Windows installer DVD

[Andrei Borzenkov]

On Thu, Oct 19, 2023 at 12:36 PM Philip Couling <couling@gmail.com> wrote:
>
> Hi
>
> Is there any reason why I can't chainload an MS Windows Installer (on
> USB)?  Currently when I try this I get "UnknownError" when I type "boot" at
> the grub command line.
>
> The MS Windows ISOs are a bit weird: found here:
> https://www.microsoft.com/en-gb/software-download/windows10ISO
>
> They are not partitioned and have a UDF filesystem instead of ISO 9660 or
> FAT32. So my hardware cannot directly boot this.  But I was assuming that
> all I would need to do would be ask grub to chainload the ISO as it has a
> UDF driver.
>
> I can read the Windows Boot media after I "insmod udf" and then
> "chainloader /efi/boot/bootx64.efi" which results in the output
> "/EndEntire".

Is it really *all* that is printed? Because grub should print the
device path and it sounds like it is empty? Always provide complete
and accurate information, not some random part of it. At the very
least there should be "file path: " somewhere before "/EndEntire".

> But when I then type "boot" I get "UnknownError".
>

grub should really print the EFI error in this case to help in
troubleshooting such issues.

> Has anyone experienced this? Any ideas about what isn't working? I freely

Assuming you are using the current upstream code (because in the past
EFI chainloader was heavily patched by distributions) grub reads the
content of EFI binary in memory, creates an instance of loaded image
from it and then calls EFI start image function. I would refrain from
guessing what could have gone wrong until you provide more precise
information.

> admit it could be a Microsoft weirdness that requires their input, I just
> wanted to exhaust options here first.
>
> Thanks