Make relocation code not trash potentially important registers

kernel/main.asm

@@ -12,7 +12,11 @@ main:
   mov ax, 18
   call malloc
 
-  ret
+  int 0x2E
+
+.endloop:
+  hlt
+  jmp .endloop
 
 %include "kernel/heap.asm"
 %include "kernel/intr.asm"

nbp.asm

@@ -7,8 +7,12 @@ org 0x0000
 ; during PXE, CS=0000 and IP=7C00
 _startup:
   xor ax, ax
-  mov ss, ax
-  mov sp, 0x0000
+
+  push cx ; byte counter
+  push si ; source offset
+  push di ; destination offset
+  push es ; destination segment
+
   mov ds, ax
   mov es, ax
 
@@ -16,16 +20,13 @@ _startup:
   mov di, 0x0500
   mov cx, (_reloc_end)
   rep movsb
-  jmp 0x0050:main
 
-_exit:
-  mov si, .message
-  call kprintf
-.loop:
-  hlt
-  jmp .loop
-.message:
-  db "Halted: Waiting for poweroff...", 0
+  pop es
+  pop di
+  pop si
+  pop cx
+
+  jmp 0x0050:main
 
 %include "kernel/main.asm"