diff options
Diffstat (limited to 'kernel/arch/x86/gdt.asm')
| -rw-r--r-- | kernel/arch/x86/gdt.asm | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/kernel/arch/x86/gdt.asm b/kernel/arch/x86/gdt.asm new file mode 100644 index 0000000..e3af8bd --- /dev/null +++ b/kernel/arch/x86/gdt.asm @@ -0,0 +1,35 @@ +; gdt.asm
+; GDT is defined here
+
+gdt_start:
+
+gdt_null: ; Null segment
+ dd 0x0
+ dd 0x0
+
+gdt_kcode: ; Kernel code segment. Kernel has seperate segment from users for ring level
+ ; flag and access byte description on osdev wiki
+ dw 0xffff ; low limit
+ dw 0x0 ;low base
+ db 0x0 ; mid base
+ db 10011010b ; order (reversed): ac, rw, dc, ex, s, privl, pr
+ db 11001111b ; flags then limit. order (reversed): 0, 0, size bit, granularity bit
+ db 0x0 ; high limit
+
+gdt_kdata: ; same as gdt_kcode but for the data segment
+ dw 0xffff ;low limit
+ dw 0x0 ;low base
+ db 0x0 ;mid base
+ db 10010010b ; order: same as code seg. changed for data seg
+ db 11001111b ; same as kcode
+ db 0x0 ; high limit
+
+gdt_end:
+
+gdt_descriptor: ; describes the gdt to the lgdt register
+ dw gdt_end - gdt_start - 1
+
+ dd gdt_start
+
+CODE_SEG equ gdt_kcode - gdt_start
+DATA_SEG equ gdt_kdata - gdt_start
\ No newline at end of file |