vbr: relocate to 0x00500

boot/vbr.asm

@@ -1,4 +1,4 @@
-org 0x7C00
+org 0
 
 fdc:		; FDC Descriptor as per ECMA-107
   jmp _startup
@@ -44,6 +44,20 @@ fdc:		; FDC Descriptor as per ECMA-107
   times (62 - ($-$$)) db " "
 
 _startup:
+  xor ax, ax
+  mov ds, ax
+  mov es, ax
+  mov cx, 0x0100
+  mov si, 0x7C00
+  mov di, 0x0500
+  rep movsw
+  jmp 0x0050:.lowstart
+.lowstart:
+  mov ax, cs
+  mov ds, ax
+  mov ss, ax
+  xor sp, sp
+
   mov [fdc.drv], dl ; backup driver number
   mov ah, 0x08
   int 0x13 ; required, QEMU detects 360kB as 1200kB with CHS 80 2 15