Add proper _exit procedure

main.asm

@@ -6,26 +6,37 @@ org 0x0000 ;	if we are not at CS:0000, CS adjustment will fix it for us
 ; es:bx		probable pxeenv+ structure
 ; ss:sp		functional stack
 
+_startup:
 ; during PXE, CS=0000 and IP=7C00
 ; adjust CS so our offsets match org setting above
-push bx ; offset register for calculations
-call near __startup_push_ip ; push ip
-__startup_push_ip:
+mov ax, _exit
+push ax ; store exit addr on stack so main will return to it
+push bx ; backup bx
+call near .push_ip
+.push_ip:
 pop bx
-sub bx, __startup_push_ip ; subtract expected value ...
+sub bx, .push_ip ; subtract expected value ...
 shr bx,1 ; shift it to 4 bits to the right
 shr bx,1
 shr bx,1
 shr bx,1
 mov ax,cs
 add ax,bx ; so we can add it to cs
-pop bx
+pop bx ; restore bx
 push ax ; cs
 mov ax, main
 push ax ; ip
+sti
 retf ; jump
 
-string_halt:
+_exit:
+  mov si, .message
+  call kprintf
+  int 0x20
+.loop:
+  hlt
+  jmp .loop
+.message:
   db "Halted: Waiting for poweroff...", 0
 
 main: