[U-Boot] [PATCH v2 04/17] x86: Rework Global Descriptor Table loading

[Simon Glass]

On Wed, Jan 4, 2012 at 11:59 AM, Graeme Russ <graeme.russ at gmail.com> wrote:
> The inline assembler is ugly and uses hard coded magic numbers. Make it more
> elegant to allow cleaner implementation of future GDT related patches. The
> compiler seems smart enough to generate the same code anyway
>
> Signed-off-by: Graeme Russ <graeme.russ at gmail.com>

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

> ---
> Changes for v2:
>  - Rebased against revised patch #3
>  - Use GDT size define instead of magic number
>  - Added commit message
>
>  arch/x86/cpu/cpu.c |   82 +++++++++++++++++++++++++++++++++------------------
>  1 files changed, 53 insertions(+), 29 deletions(-)
>
> diff --git a/arch/x86/cpu/cpu.c b/arch/x86/cpu/cpu.c
> index 209ff29..8102fb9 100644
> --- a/arch/x86/cpu/cpu.c
> +++ b/arch/x86/cpu/cpu.c
> @@ -55,35 +55,39 @@ struct gdt_ptr {
>        u32 ptr;
>  } __packed;
>
> -static void reload_gdt(void)
> +static void load_ds(u32 segment)
>  {
> -       /*
> -        * There are machines which are known to not boot with the GDT
> -        * being 8-byte unaligned.  Intel recommends 16 byte alignment
> -        */
> -       static const u64 boot_gdt[] __attribute__((aligned(16))) = {
> -               /* CS: code, read/execute, 4 GB, base 0 */
> -               [X86_GDT_ENTRY_32BIT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff),
> -               /* DS: data, read/write, 4 GB, base 0 */
> -               [X86_GDT_ENTRY_32BIT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff),
> -               /* 16-bit CS: code, read/execute, 64 kB, base 0 */
> -               [X86_GDT_ENTRY_16BIT_CS] = GDT_ENTRY(0x109b, 0, 0x0ffff),
> -               /* 16-bit DS: data, read/write, 64 kB, base 0 */
> -               [X86_GDT_ENTRY_16BIT_DS] = GDT_ENTRY(0x1093, 0, 0x0ffff),
> -       };
> -       static struct gdt_ptr gdt;
> -
> -       gdt.len = sizeof(boot_gdt)-1;
> -       gdt.ptr = (u32)&boot_gdt;
> -
> -       asm volatile("lgdtl %0\n" \
> -                    "movl $((2+1)*8), %%ecx\n" \
> -                    "movl %%ecx, %%ds\n" \
> -                    "movl %%ecx, %%es\n" \
> -                    "movl %%ecx, %%fs\n" \
> -                    "movl %%ecx, %%gs\n" \
> -                    "movl %%ecx, %%ss" \
> -                    : : "m" (gdt) : "ecx");
> +       asm volatile("movl %0, %%ds" : : "r" (segment * X86_GDT_ENTRY_SIZE));
> +}
> +
> +static void load_es(u32 segment)
> +{
> +       asm volatile("movl %0, %%es" : : "r" (segment * X86_GDT_ENTRY_SIZE));
> +}
> +
> +static void load_fs(u32 segment)
> +{
> +       asm volatile("movl %0, %%fs" : : "r" (segment * X86_GDT_ENTRY_SIZE));
> +}
> +
> +static void load_gs(u32 segment)
> +{
> +       asm volatile("movl %0, %%gs" : : "r" (segment * X86_GDT_ENTRY_SIZE));
> +}
> +
> +static void load_ss(u32 segment)
> +{
> +       asm volatile("movl %0, %%ss" : : "r" (segment * X86_GDT_ENTRY_SIZE));
> +}
> +
> +static void load_gdt(const u64 *boot_gdt, u16 num_entries)
> +{
> +       struct gdt_ptr gdt;
> +
> +       gdt.len = (num_entries * 8) - 1;
> +       gdt.ptr = (u32)boot_gdt;
> +
> +       asm volatile("lgdtl %0\n" : : "m" (gdt));
>  }
>
>  int x86_cpu_init_f(void)
> @@ -113,7 +117,27 @@ int x86_cpu_init_r(void)
>            "movl       %%eax, %%cr0\n"
>            "wbinvd\n" : : "i" (nw_cd_rst) : "eax");
>
> -       reload_gdt();
> +       /*
> +        * There are machines which are known to not boot with the GDT
> +        * being 8-byte unaligned. Intel recommends 16 byte alignment
> +        */
> +       static const u64 boot_gdt[] __aligned(16) = {
> +               /* CS: code, read/execute, 4 GB, base 0 */
> +               [X86_GDT_ENTRY_32BIT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff),
> +               /* DS: data, read/write, 4 GB, base 0 */
> +               [X86_GDT_ENTRY_32BIT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff),
> +               /* 16-bit CS: code, read/execute, 64 kB, base 0 */
> +               [X86_GDT_ENTRY_16BIT_CS] = GDT_ENTRY(0x109b, 0, 0x0ffff),
> +               /* 16-bit DS: data, read/write, 64 kB, base 0 */
> +               [X86_GDT_ENTRY_16BIT_DS] = GDT_ENTRY(0x1093, 0, 0x0ffff),
> +       };
> +
> +       load_gdt(boot_gdt, X86_GDT_NUM_ENTRIES);
> +       load_ds(X86_GDT_ENTRY_32BIT_DS);
> +       load_es(X86_GDT_ENTRY_32BIT_DS);
> +       load_fs(X86_GDT_ENTRY_32BIT_DS);
> +       load_gs(X86_GDT_ENTRY_32BIT_DS);
> +       load_ss(X86_GDT_ENTRY_32BIT_DS);
>
>        /* Initialize core interrupt and exception functionality of CPU */
>        cpu_init_interrupts();
> --
> 1.7.5.2.317.g391b14
>
> _______________________________________________
> U-Boot mailing list
> U-Boot at lists.denx.de
> http://lists.denx.de/mailman/listinfo/u-boot