From a78033acc941fc4bcf6188f1d48fd8e012673fff Mon Sep 17 00:00:00 2001
From: EmulatedSeasons <89668582+EmulatedSeasons@users.noreply.github.com>
Date: Thu, 15 Jun 2023 22:36:39 -0400
Subject: initial commit

---
 kernel/arch/i386/gdt.asm | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)
 create mode 100644 kernel/arch/i386/gdt.asm

(limited to 'kernel/arch/i386/gdt.asm')

diff --git a/kernel/arch/i386/gdt.asm b/kernel/arch/i386/gdt.asm
new file mode 100644
index 0000000..e3af8bd
--- /dev/null
+++ b/kernel/arch/i386/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
-- 
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