Remove magic numbers. Also, no code segment - not needed.

src/kernel/boot/boot.S

@@ -1,8 +1,9 @@
+#include <x86_64/memory.h>
 .intel_syntax noprefix
 
 .section .bss
-.align 0x1000
+.align PAGE_SIZE
-.skip 0x1000
+.skip PAGE_SIZE
 BootStack:
 .byte 0
 
@@ -71,10 +72,6 @@ mov cr0, eax
 
 lgdt [BootGDTp]
 
-mov eax, 0x10
-mov ss, eax
-mov ds, eax
-mov es, eax
 
 .extern long_mode_start
   jmp 0x8:long_mode_start
@@ -82,4 +79,11 @@ mov es, eax
 .code64
 long_mode_start:
 
+mov eax, 0x0
+mov ss, eax
+mov ds, eax
+mov es, eax
+mov fs, eax
+mov gs, eax
+
 jmp $

src/kernel/boot/boot_GDT.S

@@ -0,0 +1,14 @@
+#include <x86_64/gdt.h>
+#include <x86_64/memory.h>
+.intel_syntax noprefix
+
+.section .rodata
+.align PAGE_SIZE
+.global BootGDT
+.global BootGDTp
+BootGDT:
+  .long 0, 0
+  .long 0, (GDT_PRESENT | GDT_DPL(0) | GDT_CODE | GDT_LONG)
+BootGDTp:
+  .short 2*8-1
+  .quad offset BootGDT

src/kernel/boot/boot_PT.S

@@ -0,0 +1,22 @@
+#include <x86_64/memory.h>
+.intel_syntax noprefix
+
+.section .data
+.align PAGE_SIZE
+.global BootP4
+BootP4:
+  .quad offset BootP3 + (PAGE_PRESENT | PAGE_WRITE)
+  .rept ENTRIES_PER_PT - 1
+    .quad 0x0
+  .endr
+BootP3:
+  .quad offset BootP2 + (PAGE_PRESENT | PAGE_WRITE)
+  .rept ENTRIES_PER_PT - 1
+    .quad 0x0
+  .endr
+BootP2:
+  .set i, 0
+  .rept ENTRIES_PER_PT
+    .quad (i << 21 ) + (PAGE_PRESENT | PAGE_WRITE | PAGE_HUGE)
+    .set i, (i+1)
+  .endr

src/kernel/boot/boot_pagedir.S

@@ -1,33 +0,0 @@
-.intel_syntax noprefix
-
-.section .data
-.align 0x1000
-.global BootP4
-BootP4:
-  .quad offset BootP3 + 0x3
-  .rept 511
-    .quad 0x0
-  .endr
-BootP3:
-  .quad offset BootP2 + 0x3
-  .rept 511
-    .quad 0x0
-  .endr
-BootP2:
-  .set i, 0
-  .rept 512
-    .quad (i << 21 ) + 0x83
-    .set i, (i+1)
-  .endr
-
-.section .rodata
-.align 0x1000
-.global BootGDT
-.global BootGDTp
-BootGDT:
-  .quad 0
-  .quad ((1<<47) + (1<<44) + (1<<41) + (1<<43) + (1<<53))
-  .quad ((1<<47) + (1<<44) + (1<<41))
-BootGDTp:
-  .short 3*8-1
-  .quad offset BootGDT

src/kernel/include/x86_64/gdt.h

@@ -0,0 +1,6 @@
+#pragma once
+
+#define GDT_CODE      (3<<11)
+#define GDT_DPL(lvl)  ((lvl)<<13)
+#define GDT_PRESENT   (1<<15)
+#define GDT_LONG      (1<<21)

src/kernel/include/x86_64/memory.h

@@ -0,0 +1,8 @@
+#pragma once
+
+#define PAGE_PRESENT      0x001
+#define PAGE_WRITE        0x002
+#define PAGE_HUGE         0x080
+
+#define PAGE_SIZE       0x1000
+#define ENTRIES_PER_PT  512