128 bytes stack

src/boot.s

@@ -4,30 +4,47 @@
 .globl _start
 
 _start:
-jmp $0x07c0, $(real_start-_start)
+    jmp $0x07c0, $(real_start-_start)
 
 real_start:
-movw %cs, %ax
-movw %ax, %ds
-movw %ax, %es
-movw %ax, %ss
-xorw %sp, %sp
-
-// print hello world
-mov $(string_hello-_start), %ax
-mov %ax, %bp
-movw $0x1301, %ax
-movw $0x000f, %bx
-movw $12, %cx
-movw $0, %dx
-int $0x10
+    movw %cs, %ax
+    movw %ax, %ds
+    movw %ax, %es
+    movw %ax, %ss
+    movw $(stack_base-_start), %ax
+    movw %ax, %bp
+    movw %ax, %sp
+
+    call print_hello
 
 die:
-hlt
-jmp die
+    hlt
+    jmp die
+
+print_hello:
+    push %bp
+    mov %sp, %bp
+
+    mov $(string_hello-_start), %ax
+    push %bp
+    mov %ax, %bp
+    movw $0x1301, %ax
+    movw $0x000f, %bx
+    movw $12, %cx
+    movw $0, %dx
+    int $0x10
+    pop %bp
+
+    mov %bp, %sp
+    pop %bp
+    ret
 
 string_hello:
 .string "Hello World!"
 
+stack_edge:
+.space 128
+stack_base:
+
 .space 510 - (.-_start)
 .word 0xaa55