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Re: [Xen-devel] [PATCH] xen/efi: Avoid EFI stub using absolute symbols

>>> On 21.12.17 at 15:55, <julien.grall@xxxxxxxxxx> wrote:
> The EFI image should be relocatable. At the moment, all the stub is
> relocatable but one place.

Do you really mean relocatable here? Based on ...

> On both Arm64 and x86-64 (from a quick glance) , the compiler will generate
> absolute pointer in the ErrCodeToStr array. Those values are based on Xen
> view of the virtual memory and may not be the same as EFI.

... this I'm wondering whether you don't instead mean position
independent. xen.efi (on x86) wouldn't work right if there were
no relocations for this array.

> For instance, at least on Arm64, EFI will do a 1:1 mappings of the Stub.

I'm afraid it is not clear to me what "1:1 mapping" in this context
means. Isn't your problem rather than on ARM64 xen.efi's
.reloc section is empty (which presumably is a result of how it is
being built)?

> --- a/xen/common/efi/boot.c
> +++ b/xen/common/efi/boot.c
> @@ -342,7 +342,7 @@ static void __init noreturn blexit(const CHAR16 *str)
>  /* generic routine for printing error messages */
>  static void __init PrintErrMesg(const CHAR16 *mesg, EFI_STATUS ErrCode)
>  {
> -    static const CHAR16* const ErrCodeToStr[] __initconstrel = {
> +    static const CHAR16 ErrCodeToStr[][25] __initconst  = {
>          [~EFI_ERROR_MASK & EFI_NOT_FOUND]           = L"Not found",
>          [~EFI_ERROR_MASK & EFI_NO_MEDIA]            = L"The device has no 
> media",
>          [~EFI_ERROR_MASK & EFI_MEDIA_CHANGED]       = L"Media changed",

If we really wanted (needed) to go this route, at least a comment
would be needed to prevent someone later "correcting" to obvious
oddity by switching back to what we have now. But I'd prefer if this
code was left alone.


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