bug#31380: grub fails to build on i686-linux

[Mark H Weaver <mhw@netris.org>]

Hi Ludovic,

ludo@gnu.org (Ludovic Courtès) writes:

> Mark H Weaver <mhw@netris.org> skribis:
>
>> Here's a proposed patch that I hope will fix the problem, although I'm
>> unable to easily test it because I no longer use binary substitutes, and
>> I have not yet built the core packages for i686-linux.
>>
>> However, I've applied this patch to my x86_64 system, and verified that
>> it does not cause any problems there.
>>
>> Would someone be willing to test it and report back?
>
> I tried it and it initially failed to build with:
[...]
> I fixed this and pushed as a7c8716928a240ba2c36d360e4ffeb447671fa6b.

Thanks very much!  Hydra has now successfully built GRUB on i686-linux,
so I'm closing this bug.

> I wanted to try ‘guix system vm-image -s i686-linux’ on my x86_64 laptop
> to make sure GRUB runs fine.  Unfortunately, I stumbled upon another
> issue, which is that qemu-system-i386 built for i686-linux segfaults at
> startup:
[...]
> I was able to work around it by disabling KVM:
> 
> diff --git a/gnu/build/vm.scm b/gnu/build/vm.scm
> index 73d0191de..a675111d4 100644
> --- a/gnu/build/vm.scm
> +++ b/gnu/build/vm.scm
> @@ -104,7 +104,8 @@ the #:references-graphs parameter of 'derivation'."
>        ;; hardware virtualization to still use these commands.  KVM support is
>        ;; still buggy on some ARM32 boards. Do not use it even if available.
>        ,@(if (and (file-exists? "/dev/kvm")
> -                 (not target-arm32?))
> +                 (not target-arm32?)
> +                 (not (string-suffix? "-i386" qemu)))
>              '("-enable-kvm")
>              '())
>  
> I suspect a KVM bug in Linux 4.17 though, because running the same
> ‘qemu-system-i386’ binary under strace works…  Perhaps worth applying
> the patch above in the meantime, WDYT?

It would be better to auto-detect the presence of KVM support at run
time, but that's a wishlist item that deserves its own ticket.  This is
good enough for now.

> Anyway, with this patch I successfully run:
>
>   guix system vm-image gnu/system/examples/bare-bones.tmpl -s i686-linux
>
> and confirmed that the resulting image would boot through GRUB.

Sounds great, thanks again!

     Mark