Simplest possible long-mode entry

src/kernel/boot/boot.S

@@ -53,4 +53,33 @@ mov esp, offset BootStack
 call check_cpuid
 call check_longmode
 
+mov eax, cr4
+or eax, 1<<5
+mov cr4, eax
+
+mov eax, offset BootP4
+mov cr3, eax
+
+mov ecx, 0x0C0000080
+rdmsr
+or eax, 1<<8
+wrmsr
+
+mov eax, cr0
+or eax, 1<<31
+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
+
+.code64
+long_mode_start:
+
 jmp $

src/kernel/boot/boot_pagedir.S

@@ -0,0 +1,33 @@
+.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