[U-Boot] [PATCH v2 11/17] x86: Tweak IDT and GDT for alignment and readability

[Simon Glass]

On Wed, Jan 4, 2012 at 11:59 AM, Graeme Russ <graeme.russ at gmail.com> wrote:
> Signed-off-by: Graeme Russ <graeme.russ at gmail.com>

Acked-by: Simon Glass <sjg at chromium.org>

> ---
> Changes for v2:
>  - Renamed to better reflect nature of changes
>
>  arch/x86/cpu/interrupts.c |    2 +-
>  arch/x86/cpu/start16.S    |   57 +++++++++++++++++++++++++++++++++++---------
>  2 files changed, 46 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/cpu/interrupts.c b/arch/x86/cpu/interrupts.c
> index e0958eb..43ec3f8 100644
> --- a/arch/x86/cpu/interrupts.c
> +++ b/arch/x86/cpu/interrupts.c
> @@ -174,7 +174,7 @@ struct desc_ptr {
>        unsigned short segment;
>  } __packed;
>
> -struct idt_entry idt[256] __attribute__((aligned(16)));
> +struct idt_entry idt[256] __aligned(16);
>
>  struct desc_ptr idt_ptr;
>
> diff --git a/arch/x86/cpu/start16.S b/arch/x86/cpu/start16.S
> index 33e53cd..cc393ff 100644
> --- a/arch/x86/cpu/start16.S
> +++ b/arch/x86/cpu/start16.S
> @@ -86,7 +86,11 @@ gdt_ptr:
>        .word   0x20            /* limit (32 bytes = 4 GDT entries) */
>        .long   BOOT_SEG + gdt  /* base */
>
> -       /* The GDT table ...
> +/* Some CPUs are picky about GDT alignment... */
> +.align 16
> +gdt:
> +       /*
> +        * The GDT table ...
>         *
>         *       Selector       Type
>         *       0x00           NULL
> @@ -94,17 +98,46 @@ gdt_ptr:
>         *       0x10           32bit code
>         *       0x18           32bit data/stack
>         */
> +       /* The NULL Desciptor - Mandatory */
> +       .word   0x0000          /* limit_low */
> +       .word   0x0000          /* base_low */
> +       .byte   0x00            /* base_middle */
> +       .byte   0x00            /* access */
> +       .byte   0x00            /* flags + limit_high */
> +       .byte   0x00            /* base_high */
>
> -gdt:
> -       .word   0, 0, 0, 0      /* NULL  */
> -       .word   0, 0, 0, 0      /* unused */
> +       /* Unused Desciptor - (matches Linux) */
> +       .word   0x0000          /* limit_low */
> +       .word   0x0000          /* base_low */
> +       .byte   0x00            /* base_middle */
> +       .byte   0x00            /* access */
> +       .byte   0x00            /* flags + limit_high */
> +       .byte   0x00            /* base_high */
>
> -       .word   0xFFFF          /* 4Gb - (0x100000*0x1000 = 4Gb) */
> -       .word   0               /* base address = 0 */
> -       .word   0x9B00          /* code read/exec */
> -       .word   0x00CF          /* granularity = 4096, 386 (+5th nibble of limit) */
> +       /*
> +        * The Code Segment Descriptor:
> +        * - Base   = 0x00000000
> +        * - Size   = 4GB
> +        * - Access = Present, Ring 0, Exec (Code), Readable
> +        * - Flags  = 4kB Granularity, 32-bit
> +        */
> +       .word   0xffff          /* limit_low */
> +       .word   0x0000          /* base_low */
> +       .byte   0x00            /* base_middle */
> +       .byte   0x9b            /* access */
> +       .byte   0xcf            /* flags + limit_high */
> +       .byte   0x00            /* base_high */
>
> -       .word   0xFFFF          /* 4Gb - (0x100000*0x1000 = 4Gb) */
> -       .word   0x0             /* base address = 0 */
> -       .word   0x9300          /* data read/write */
> -       .word   0x00CF          /* granularity = 4096, 386 (+5th nibble of limit) */
> +       /*
> +        * The Data Segment Descriptor:
> +        * - Base   = 0x00000000
> +        * - Size   = 4GB
> +        * - Access = Present, Ring 0, Non-Exec (Data), Writable
> +        * - Flags  = 4kB Granularity, 32-bit
> +        */
> +       .word   0xffff          /* limit_low */
> +       .word   0x0000          /* base_low */
> +       .byte   0x00            /* base_middle */
> +       .byte   0x93            /* access */
> +       .byte   0xcf            /* flags + limit_high */
> +       .byte   0x00            /* base_high */
> --
> 1.7.5.2.317.g391b14
>
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