Re: [Xen-devel] [PATCH V3] xen/arm: arm64: Update the Image header

[Julien Grall <julien.grall@xxxxxxx>]

Hello Peng,

On 12/09/2016 11:43, Peng Fan wrote:
> According to Linux Kernel, Documentation/arm64/booting.txt
> "
> When image_size is zero, a bootloader should attempt to keep as much
> memory as possible free for use by the kernel immediately after the
> end of the kernel image. The amount of space required will vary
> depending on selected features, and is effectively unbound.
> "
> This will consumes some memory and time, for example,
> When booting xen from U-Boot, U-Boot will use the image size
> info. Because this information is lacked in XEN image,U-Boot
> assume the image size is 16MB to memmove, which will cost lots
> time on simulation platform.
>
> The flags field is also filled with value 0xA,
> Bit3(physical placement):   1
> Bit2-1(Page size):          1
> Bit0(endianness):           0
Please explain in the commit message why those values and, for instance, 
not 0 for Bit3.
> Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> ---
>
> V3:
>  Drop the image.h macros.h from Linux, included in V2.
>  Only update image size and flags entry. offset was kept 0 as before.
>  Only little endian supported.
>
> V2:
>  According to Linux Kernel, a2c1d73b94ed49 "arm64: Update the Image header",
>  included unneccessary stuff.
>
>  xen/arch/arm/arm64/head.S | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
> index 91e2817..2cd3699 100644
> --- a/xen/arch/arm/arm64/head.S
> +++ b/xen/arch/arm/arm64/head.S
> @@ -115,8 +115,8 @@ 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 */
NIT: Please use _start here.

> +       .quad   0xa                  /* Informative flags(Physical placement 1, 
> 4KB, LE), little-endian */
>          .quad   0                    /* reserved */
>          .quad   0                    /* reserved */
>          .quad   0                    /* reserved */
Regards,

--
Julien Grall

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