check gpt partition magic

boot0.s

@@ -46,7 +46,7 @@ bits 16
   mov di, 0x00
   mov ah, 0x08
   int 0x13
-  jc panic
+  jc .panic
   and cl, 0x3f     ; sectors per track
   mov [bp + 1], cl
   movzx bx, dh
@@ -70,7 +70,7 @@ bits 16
   mov bx, 0x7e00
   mov dl, [bp] ; drive number
   int 0x13
-  jc panic
+  jc .panic
 
   ; head = temp % number of heads
   ; cylinder = temp / number of heads
@@ -80,6 +80,12 @@ bits 16
   mov ax, 0x0003
   int 0x10
 
+  mov cx, 8
+  mov si, .gpt_magic
+  mov di, 0x7e00
+  repe cmpsb
+  jne .panic
+
   ; mov word fs:[0x0000], 0xc048
   ; mov word fs:[0x0002], 0xc069
   mov al, [0x7e00]
@@ -90,7 +96,7 @@ bits 16
   mov byte fs:[0x0004], al
   hlt
 
-panic:
+.panic:
   mov ax, 0x0003
   int 0x10
   mov ax, 0xb800
@@ -118,6 +124,9 @@ panic:
   ;   - Boot from UEFI
   ;   - Boot on non-GPT partitioned disk
 
+.gpt_magic:
+  db "EFI PART"
+
   ; MBR bootstrap field is 440 bytes long
   %if ($ - $$) > 440
   %error "exceeded mbr bootstrap field size"