diff --git a/service/ptos/arch/amd64/cpu/locore.S b/service/ptos/arch/amd64/cpu/locore.S
index 405903e..bc9c5fd 100644
--- a/service/ptos/arch/amd64/cpu/locore.S
+++ b/service/ptos/arch/amd64/cpu/locore.S
@@ -9,6 +9,89 @@
     .text
     .globl MdBspEntry
 MdBspEntry:
-    cli
-    hlt
-    jmp MdBspEntry
+    cli             /* Disable interrupts on startup */
+    cld             /* Just in case, can't predict the state */
+    xor %rbp, %rbp  /* Terminate callstack for traces */
+
+    lea g_GDTR(%rip), %rdi
+    call MdGdtLoad
+1:  hlt
+    jmp 1b
+
+    .text
+    .globl MdGdtLoad
+MdGdtLoad:
+    push %r12
+    push %r13
+    push %r14
+    push %r15
+    push %rbx
+    push %rbp
+
+    lgdt (%rdi)
+    push $0x08
+    lea 1f(%rip), %rbx
+    push %rbx
+    lretq
+1:  mov $0x10, %ax
+    mov %ax, %ds
+    mov %ax, %es
+    mov %ax, %ss
+    mov %ax, %fs
+    xor %ax, %ax
+    mov %ax, %gs
+
+    pop %rbp
+    pop %rbx
+    pop %r15
+    pop %r14
+    pop %r13
+    pop %r12
+    retq
+
+     .section .data
+    .globl g_GDT
+g_GDT:
+.NULL:
+    .word 0x0000
+    .word 0x0000
+    .byte 0x00
+    .byte 0b00000000
+    .byte 0b00000000
+    .byte 0x00
+.CODE:
+    .word 0x0000
+    .word 0x0000
+    .byte 0x00
+    .byte 0b10011010
+    .byte 0b00100000
+    .byte 0x00
+.DATA:
+    .word 0x0000
+    .word 0x0000
+    .byte 0x00
+    .byte 0b10010010
+    .byte 0b00000000
+    .byte 0x00
+.UCODE:
+    .word 0x0000
+    .word 0x0000
+    .byte 0x00
+    .byte 0b11111010
+    .byte 0b10101111
+    .byte 0x00
+.UDATA:
+    .word 0x0000
+    .word 0x0000
+    .byte 0x00
+    .byte 0b11110010
+    .byte 0b00000000
+    .byte 0x00
+.TSS:
+    .quad 0x00
+    .quad 0x00
+
+    .globl g_GDTR
+g_GDTR:
+    .word g_GDTR - g_GDT
+    .quad g_GDT