[Xen-devel] Xen boot failure on QEMU (WAS: Re: [PATCH v3] xen:arm: Populate arm64 image header)

[Julien Grall <julien.grall@xxxxxxx>]

(+ Peter Maydell and Stefano)

Hi Steward,

Thank you for the bug report.

On 05/10/2018 23:17, Stewart Hildebrand wrote:
> On 11/09/2018 17:48, Amit Singh Tomar wrote:
> > diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
> > index d63734f..ef87b5c 100644
> > --- a/xen/arch/arm/arm64/head.S
> > +++ b/xen/arch/arm/arm64/head.S
> > @@ -120,8 +127,8 @@ efi_head:
> >            add     x13, x18, #0x16
> >            b       real_start           /* branch to kernel start */
> >            .quad   0                    /* Image load offset from start of RAM 
> > */
> > -        .quad   0                    /* reserved */
> > -        .quad   0                    /* reserved */
> > +        .quad   _end - start         /* Effective size of kernel image, 
> > little-endian */
> > +        .quad   __HEAD_FLAGS         /* Informative flags, little-endian */
> >            .quad   0                    /* reserved */
> >            .quad   0                    /* reserved */
> >            .quad   0                    /* reserved */
> Since 17bd254a xen:arm: Populate arm64 image header, qemu-system-aarch64 has 
> not been too happy about booting Xen.
>
> Trying to launch qemu-system-aarch64 gives the following error:
> rom: requested regions overlap (rom bootloader. free=0x00000000400d0150, 
> addr=0x0000000040000000)
> qemu-system-aarch64: rom check and register reset failed
>
> Reverting 17bd254a allowed it to boot again. Alternatively, setting the image 
> offset to some value allowed it to boot again.
>   
> diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
> index ef87b5c..8879c77 100644
> --- a/xen/arch/arm/arm64/head.S
> +++ b/xen/arch/arm/arm64/head.S
> @@ -126,7 +126,7 @@ efi_head:
>            */
>           add     x13, x18, #0x16
>           b       real_start           /* branch to kernel start */
> -        .quad   0                    /* Image load offset from start of RAM */
> +        .quad   0x00080000           /* Image load offset from start of RAM */
>           .quad   _end - start         /* Effective size of kernel image, 
> little-endian */
>           .quad   __HEAD_FLAGS         /* Informative flags, little-endian */
>           .quad   0                    /* reserved */
>
> I'm not sure if this is a fault of qemu, or if Xen should put some value in the 
> image load offset field?
Per the Linux arm64 booting protocol [1], the load offset can definitely 
be 0. The bootloader (here QEMU) should not assume a specific text 
offset, Linux actually provides an option to randomize the text offset 
in order to test that assumption (see ARM64_RANDOMIZE_TEXT_OFFSET).
I have CCed Stefano and Peter who could give more details on how QEMU is 
handling the Image protocol.
> For reference, I'm using the following script to build and launch qemu+Xen 
> https://gist.github.com/stewdk/110f43e0cc1d905fc6ed4c7e10d8d35e
Cheers,

[1] https://www.kernel.org/doc/Documentation/arm64/booting.txt

--
Julien Grall

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