stos/amd64: Load the GDT

Signed-off-by: Chloe M. <chloe@mensia.org>

paw/stos/arch/amd64/cpu/locore.S

@@ -12,6 +12,87 @@ _start:
     cli                /* Just in case */
     xor %rbp, %rbp     /* Terminate callstack */
 
+    lea g_GDTR(%rip), %rdi
+    call MdGdtLoad
+
     mfence      /* Flush caches */
 1:  cli         /* Disable interrupts */
     hlt         /* Suspend processor */
+
+    .text
+    .globl MdGdtLoad
+MdGdtLoad:
+    push %r12
+    push %r13
+    push %r14
+    push %r15
+    push %rbx
+    push %rbp
+
+    lgdt (%rdi)                 /* Load our own GDT */
+    push $0x08                  /* Kernel CS */
+    lea 1f(%rip), %rbx          /* Drop point */
+    push %rbx                   /* RIP */
+    lretq                       /* Flush prefetch + reload CS */
+1:  mov $0x10, %ax              /* Kernel DS */
+    mov %ax, %ds
+    mov %ax, %es
+    mov %ax, %ss
+    mov %ax, %fs
+    xor %ax, %ax
+    mov %ax, %gs
+
+    pop %rbp
+    pop %rbx
+    pop %r15
+    pop %r14
+    pop %r13
+    pop %r12
+    retq
+
+     .section .data
+    .globl g_GDT
+g_GDT:
+.NULL:
+    .word 0x0000
+    .word 0x0000
+    .byte 0x00
+    .byte 0b00000000
+    .byte 0b00000000
+    .byte 0x00
+.CODE:
+    .word 0x0000
+    .word 0x0000
+    .byte 0x00
+    .byte 0b10011010
+    .byte 0b00100000
+    .byte 0x00
+.DATA:
+    .word 0x0000
+    .word 0x0000
+    .byte 0x00
+    .byte 0b10010010
+    .byte 0b00000000
+    .byte 0x00
+.UCODE:
+    .word 0x0000
+    .word 0x0000
+    .byte 0x00
+    .byte 0b11111010
+    .byte 0b10101111
+    .byte 0x00
+.UDATA:
+    .word 0x0000
+    .word 0x0000
+    .byte 0x00
+    .byte 0b11110010
+    .byte 0b00000000
+    .byte 0x00
+.TSS:
+    .quad 0x00
+    .quad 0x00
+
+    .globl g_GDTR
+g_GDTR:
+    .word g_GDTR - g_GDT
+    .quad g_GDT