From 990a74798cfc9f8cedb1f8ff16765e4012924da8 Mon Sep 17 00:00:00 2001
From: antifallobst <antifallobst@systemausfall.org>
Date: Sun, 5 Mar 2023 15:57:56 +0100
Subject: [PATCH] docs: documented GDT changes

---
 .wiki/Kernel-documentation.md | 38 ++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/.wiki/Kernel-documentation.md b/.wiki/Kernel-documentation.md
index 1380b7f..fca17ef 100644
--- a/.wiki/Kernel-documentation.md
+++ b/.wiki/Kernel-documentation.md
@@ -1068,8 +1068,44 @@ OSDev Wiki: [Global Descriptor Table](https://wiki.osdev.org/GDT)
 - **Null**
 - **Kernel Code** - Readable
 - **Kernel Data** - Readable + Writable
+- **User Null**
+- **User Code** - Readable
+- **User Data** - Readable + Writable
 
-NoxOS uses the GDT loaded by limine, because in 64 bit mode a GDT is only needed for backwards compatability.
+#### `gdt_descriptor_T` - struct [packed]
+
+| Name   | Type     | Description                                         |
+|--------|----------|-----------------------------------------------------|
+| size   | uint16_t | The tables size in bytes (-1)                       |
+| offset | uint64_t | The virtual address, where the table lies in memory |
+
+
+#### `gdt_entry_T` - struct [packed]
+| Name         | Type     | Description                                                  |
+|--------------|----------|--------------------------------------------------------------|
+| limit0       | uint16_t | Can be ignored in long mode                                  |
+| base0        | uint16_t | Can be ignored in long mode                                  |
+| base1        | uint8_t  | Can be ignored in long mode                                  |
+| access       | uint8_t  | Specifies permissions (details in osdev wiki)                |
+| limit1_flags | uint8_t  | The first 4 bits can be ignored and the last 4 specify flags |
+| base2        | uint8_t  | Can be ignored in long mode                                  |
+
+#### `gdt_T` - struct [packed / page aligned]
+| Name        | Type        | Description                              |
+|-------------|-------------|------------------------------------------|
+| null        | gdt_entry_T | The entry for `GDT_SELECTOR_NULL`        |
+| kernel_code | gdt_entry_T | The entry for `GDT_SELECTOR_KERNEL_CODE` |
+| kernel_data | gdt_entry_T | The entry for `GDT_SELECTOR_KERNEL_DATA` |
+| user_null   | gdt_entry_T | The entry for `GDT_SELECTOR_USER_NULL`   |
+| user_code   | gdt_entry_T | The entry for `GDT_SELECTOR_USER_CODE`   |
+| user_data   | gdt_entry_T | The entry for `GDT_SELECTOR_USER_DATA`   |
+
+#### `g_default_gdt` - global variable
+The systems GDT.
+
+#### `gdt_init` - function (void)
+Populates and loads `g_default_gdt`.
+This will also set all the data segment registers to 0x10 (Kernel Data) and `cs` to 0x08 (Kernel Code).
 
 ### interrupts.h
 This header contains all the stuff, needed to init and handle Interrupts.