[U-Boot] [PATCH 12/39] x86: Tidy up global descriptor table setup

[Bin Meng]

On Fri, Nov 7, 2014 at 4:20 AM, Simon Glass <sjg at chromium.org> wrote:
> This code is a little muddled, so tidy it up. Make sure that we put the
> GDT in the right place and set it up properly.
>
> Signed-off-by: Simon Glass <sjg at chromium.org>
> ---
>
>  arch/x86/cpu/start.S | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/cpu/start.S b/arch/x86/cpu/start.S
> index 62ac4cd..c41e1ae 100644
> --- a/arch/x86/cpu/start.S
> +++ b/arch/x86/cpu/start.S
> @@ -69,6 +69,16 @@ car_init_ret:
>          * We now have CONFIG_SYS_CAR_SIZE bytes of Cache-As-RAM (or SRAM,
>          * or fully initialised SDRAM - we really don't care which)
>          * starting at CONFIG_SYS_CAR_ADDR to be used as a temporary stack
> +        * and early malloc area.
> +        *
> +        * Stack grows down from top of CAR. We have:
> +        *
> +        * top-> CONFIG_SYS_CAR_ADDR + CONFIG_SYS_CAR_SIZE
> +        *      global_data
> +        *      x86 global descriptor table
> +        *      early malloc area
> +        *      stack
> +        * bottom-> CONFIG_SYS_CAR_ADDR
>          */
>
>         /* Stack grows down from top of CAR */
> @@ -86,12 +96,16 @@ car_init_ret:
>         movl    %esp, %edi
>         rep     stosb
>
> -       /* Setup first parameter to setup_gdt */
> +       /* Setup first parameter to setup_gdt, pointer to global_data */
>         movl    %esp, %eax
>
>         /* Reserve space for global descriptor table */
>         subl    $X86_GDT_SIZE, %esp
>
> +       /* Align temporary global descriptor table to 16-byte boundary */
> +       andl    $0xfffffff0, %esp
> +       movl    %esp, %ecx
> +
>  #if defined(CONFIG_SYS_MALLOC_F_LEN)
>         subl    $CONFIG_SYS_MALLOC_F_LEN, %esp
>         movl    %eax, %edx
> @@ -103,14 +117,13 @@ car_init_ret:
>         andl    $0xfffffff0, %esp
>
>         /* Set second parameter to setup_gdt */
> -       movl    %esp, %edx
> +       movl    %ecx, %edx
>
>         /* Setup global descriptor table so gd->xyz works */
>         call    setup_gdt
>
>         /* Set parameter to board_init_f() to boot flags */
>         xorl    %eax, %eax
> -       movw    %bx, %ax
>
>         /* Enter, U-boot! */
>         call    board_init_f
> --

Reviewed-by: Bin Meng <bmeng.cn at gmail.com>