From 5fc5a3be0e499dc259e2073bb39a13577ef20b35 Mon Sep 17 00:00:00 2001
From: starnakin <camille@chauvet.pro>
Date: Tue, 10 Sep 2024 11:19:23 +0200
Subject: [PATCH] fix: cringe gdt and and stack gdt

---
 headers/gdt.h  |  4 ++++
 src/gdt/gdt.c  | 47 ++++++++++++++++++++++++++++++++++++-----------
 src/gdt/sgdt.s | 12 ------------
 3 files changed, 40 insertions(+), 23 deletions(-)
 delete mode 100644 src/gdt/sgdt.s

diff --git a/headers/gdt.h b/headers/gdt.h
index 53b61e3..9cc0aa1 100644
--- a/headers/gdt.h
+++ b/headers/gdt.h
@@ -2,6 +2,10 @@
 
 #include <stdint.h>
 
+#define GDT_BASE 0x00000800
+//              sizeof(Segment Descriptor) * nb(Segment Descriptor)
+#define GDT_SIZE 8 * 7
+
 struct gdt_entry {
     uint32_t limit;
     uint32_t base;
diff --git a/src/gdt/gdt.c b/src/gdt/gdt.c
index d0d0c2c..21c7b5e 100644
--- a/src/gdt/gdt.c
+++ b/src/gdt/gdt.c
@@ -1,5 +1,6 @@
 #include "gdt.h"
 #include "kprintf.h"
+#include "string.h"
 
 extern void setGdt(void *);
 
@@ -27,44 +28,68 @@ void encodeGdtEntry(uint8_t *target, struct gdt_entry source)
     // Encode the flags
     target[6] |= (source.flags << 4);
 }
-//                  sizeof(Segment Descriptor) * nb(Segment Descriptor)
-uint8_t *gdt_entries = (uint8_t *) 0x00000800;
-struct gdt_descriptor gdtr; 
+
+uint8_t gdt_entries[8][7];
+struct gdt_descriptor gdtr;
 
 void initGdt()
 {
-    gdtr.size = 8 * 5 - 1;
-    gdtr.base = (uint32_t) &gdt_entries;
+    gdtr.size = GDT_SIZE - 1;
+    gdtr.base = GDT_BASE;
 
     struct gdt_entry gdt_entry_null_descriptor = { .base = 0,
                                                    .limit = 0x00000000,
                                                    .access_byte = 0x00,
                                                    .flags = 0x0};
-    encodeGdtEntry(gdt_entries + 0x0000, gdt_entry_null_descriptor);
+    encodeGdtEntry(gdt_entries[0], gdt_entry_null_descriptor);
 
     struct gdt_entry gdt_entry_kernel_mode_code_segment = { .base = 0,
                                                             .limit = 0xFFFFF,
                                                             .access_byte = 0x9A,
                                                             .flags = 0xC };
-    encodeGdtEntry(gdt_entries + 0x0008, gdt_entry_kernel_mode_code_segment);
+    encodeGdtEntry(gdt_entries[1], gdt_entry_kernel_mode_code_segment);
 
     struct gdt_entry gdt_entry_kernel_mode_data_segment = { .base = 0,
                                                             .limit = 0xFFFFF,
                                                             .access_byte = 0x92,
                                                             .flags = 0xC };
-    encodeGdtEntry(gdt_entries + 0x0010, gdt_entry_kernel_mode_data_segment);
+    encodeGdtEntry(gdt_entries[2], gdt_entry_kernel_mode_data_segment);
+
+    struct gdt_entry gdt_entry_kernel_mode_stack_segment = { .base = 0x0,
+                                                             .limit = 0x0,
+                                                             .access_byte = 0x97,
+                                                             .flags = 0x0D };
+    encodeGdtEntry(gdt_entries[3], gdt_entry_kernel_mode_data_segment);
 
     struct gdt_entry gdt_entry_user_mode_code_segment = { .base = 0,
                                                           .limit = 0xFFFFF,
                                                           .access_byte = 0xFA,
                                                           .flags = 0xC };
-    encodeGdtEntry(gdt_entries + 0x0018, gdt_entry_user_mode_code_segment);
+    encodeGdtEntry(gdt_entries[4], gdt_entry_user_mode_code_segment);
 
     struct gdt_entry gdt_entry_user_mode_data_segment = { .base = 0,
                                                           .limit = 0xFFFFF,
                                                           .access_byte = 0xF2,
                                                           .flags = 0xC };
-    encodeGdtEntry(gdt_entries + 0x0020, gdt_entry_user_mode_data_segment);
+    encodeGdtEntry(gdt_entries[5], gdt_entry_user_mode_data_segment);
 
-    setGdt(&gdtr);
+    struct gdt_entry gdt_entry_user_mode_stack_segment = { .base = 0x0,
+                                                           .limit = 0x0,
+                                                           .access_byte = 0xF7,
+                                                           .flags = 0x0D };
+    encodeGdtEntry(gdt_entries[6], gdt_entry_user_mode_data_segment);
+
+    memcpy((void *) gdtr.base, (void *) gdt_entries, (size_t) GDT_SIZE);
+
+    /* load the gdtr registry */
+    asm("lgdtl (gdtr)");
+
+    /* initiliaz the segments */
+    asm("   movw $0x10, %ax    \n \
+            movw %ax, %ds    \n \
+            movw %ax, %es    \n \
+            movw %ax, %fs    \n \
+            movw %ax, %gs    \n \
+            ljmp $0x08, $next    \n \
+            next:        \n");
 }
\ No newline at end of file
diff --git a/src/gdt/sgdt.s b/src/gdt/sgdt.s
deleted file mode 100644
index 87829d9..0000000
--- a/src/gdt/sgdt.s
+++ /dev/null
@@ -1,12 +0,0 @@
-.globl setGdt
-
-gdtr: .word 0          # For limit storage
-      .long 0          # For base storage
-
-setGdt:
-   movw 4(%esp), %ax   # Move the word at [esp + 4] into AX
-   movw %ax, gdtr      # Move AX into gdtr
-   movl 8(%esp), %eax  # Move the double word at [esp + 8] into EAX
-   movl %eax, gdtr + 2 # Move EAX into gdtr + 2
-   lgdt gdtr           # Load the GDT
-   ret
\ No newline at end of file