From afcf0bea094d6cebba8c8822552a06f73a598fbd Mon Sep 17 00:00:00 2001
From: Nathan Singer <nathan.r.singer@gmx.com>
Date: Thu, 29 May 2025 10:17:18 -0400
Subject: [PATCH] reimplements the gdt

---
 kernel/arch/gdt/gdt.s             | 23 +++++++++++++++++++++++
 kernel/arch/{ => gdt}/gdt_entry.c |  0
 kernel/kmain.c                    | 14 ++++++++++++++
 3 files changed, 37 insertions(+)
 create mode 100644 kernel/arch/gdt/gdt.s
 rename kernel/arch/{ => gdt}/gdt_entry.c (100%)

diff --git a/kernel/arch/gdt/gdt.s b/kernel/arch/gdt/gdt.s
new file mode 100644
index 0000000..86db7f4
--- /dev/null
+++ b/kernel/arch/gdt/gdt.s
@@ -0,0 +1,23 @@
+gdtr 	DW 0 ; limit store
+	DD 0 ; base storage
+
+global setGdt
+setGdt:
+	mov ax, [esp + 4]
+	mov [gdtr], ax
+	mov eax, [esp + 8]
+	mov [gdtr + 2], eax
+	lgdt [gdtr]
+	ret
+
+global reloadSegments
+reloadSegments:
+	jmp 0x08:.reload_CS ; 0x08 is a stand in for the code segment
+.reload_CS:
+	mov ax, 0x10 ; stand in for the data segment
+	mov ds, ax
+	mov es, ax
+	mov fs, ax
+	mov gs, ax
+	mov ss, ax
+	ret
diff --git a/kernel/arch/gdt_entry.c b/kernel/arch/gdt/gdt_entry.c
similarity index 100%
rename from kernel/arch/gdt_entry.c
rename to kernel/arch/gdt/gdt_entry.c
diff --git a/kernel/kmain.c b/kernel/kmain.c
index 44a4f48..34911c4 100644
--- a/kernel/kmain.c
+++ b/kernel/kmain.c
@@ -1,10 +1,24 @@
 #include <stdio.h>
+#include <stdint.h>
 
 #include <kernel/tty.h>
 #include <kernel/serial.h>
+#include <kernel/x86/gdt.h>
+
+uint64_t gdt[5];
 
 void kmain(void)
 {
+	gdt[0] = create_descriptor(0, 0, 0); // null
+	gdt[1] = create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL0));
+	gdt[2] = create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL0));
+	gdt[3] = create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL3));
+	gdt[4] = create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL3));
+
+	setGdt((sizeof(uint64_t) * 5) - 1, &(gdt[0]));
+	reloadSegments();
+	
+
 	terminal_initialize();
 	serial_initialize();