Re: [Xen-devel] [PATCH RFC 15/19] Add PE/COFF header in head.S

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Sat, 2014-06-28 at 02:25 +0100, Roy Franz wrote:
> This patch adds a simple PE/COFF header in head.S.  PE/COFF linker support
> is not available for arm64, so a native build is not possible.  Also, this
> allows the binary to be both a PE/COFF EFI application, and a normal Image
> file bootable like a Linux kernel.  The arm and arm64 Linux kernels use the
> same methodology to create a single image that is both an EFI application and
> a zImage/Image file.

This looks good to me. A few minor comments:

Some of the whitespace is off (please use space and not hard tabs
throughout)

I think we could perhaps get rid of CONFIG_EFI_STUB at least at the
arm64 subarch level. We don't in general support the same level of
configurability in Xen as Linux -- it's mostly just a single
configuration for everyone. It'd need to be retain at the arch level to
cope with arm32 not doing efi, but removing it here would make things
simpler I think?

Would it be possible to find sort of link/reference to a spec for the
header structs which you are adding and stick them in comments before
each one please.

> 
> Signed-off-by: Roy Franz <roy.franz@xxxxxxxxxx>
> ---
>  xen/arch/arm/arm64/head.S | 118 
> +++++++++++++++++++++++++++++++++++++++++++++-
>  xen/arch/arm/xen.lds.S    |   1 +
>  2 files changed, 117 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
> index 2a13527..9b88aeb 100644
> --- a/xen/arch/arm/arm64/head.S
> +++ b/xen/arch/arm/arm64/head.S
> @@ -84,7 +84,7 @@
>  #endif /* !CONFIG_EARLY_PRINTK */
>  
>          /*.aarch64*/
> -
> +#define CONFIG_EFI_STUB
>          /*
>           * Kernel startup entry point.
>           * ---------------------------
> @@ -100,12 +100,24 @@
>           */
>  
>          .global start
> +efi_stub_entry:  /* Dummy symbol so we can compile before actual stub added 
> */
>  start:
> +#ifdef CONFIG_EFI_STUB
>          /*
>           * DO NOT MODIFY. Image header expected by Linux boot-loaders.
>           */
> -        b       real_start           /* branch to kernel start, magic */
> +efi_head:
> +        /*
> +         * This add instruction has no meaningful effect except that
> +         * its opcode forms the magic "MZ" signature of a PE/COFF file
> +      * that is required for UEFI applications.
> +         */
> +        add     x13, x18, #0x16

I love this hack ;-)

Ian.


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