implement util function to print numbers with header

Makefile

@@ -97,7 +97,7 @@ $(OBJ_DIR)/%.o: $(SRC_DIR)/%.s
 	$(AS) $(ASFLAGS) -o $@ $<
 	$(OBJCOPY) --remove-section .note.gnu.property $@
 
-MBR_TEST_OBJ		=	obj/mbr_test.o obj/serial.o obj/itoa.o
+MBR_TEST_OBJ		=	obj/mbr_test.o obj/serial.o obj/itoa.o obj/util.o
 
 mbr_test: $(MBR_TEST_OBJ) $(DISK)
 	$(LD) -T src/mbr_test.ld -o $(BIN_DIR)/mbr_test.bin $(MBR_TEST_OBJ)

src/itoa.s

@@ -7,6 +7,7 @@
 
 # eax - number
 # ecx - base
+# return - ds:si pointing to string number
 itoa:
     push %bx
     xor %edx, %edx
@@ -36,7 +37,7 @@ itoa:
     # we return ptr to string, since we're pushing chars in reverse, therefore
     # beginning of string will change
     inc %di
-    mov %di, %ax
+    mov %di, %si
 
     pop %bx
     ret
@@ -45,4 +46,4 @@ itoa:
 .comm       itoa_result,        ITOA_BUFFER_SIZE
 
 .section .rodata
-numbers:    .ascii "0123456789ABCDEF"
+numbers:    .ascii "0123456789ABCDEF"

src/mbr_test.s

@@ -52,14 +52,8 @@ entry:
 
     # it's working fixed disk, lets print its number
     movw disk_id, %ax
-    mov $10, %cx
-    call itoa
-
-    mov %ax, %si
-    call prints
-
-    mov $'\n', %al
-    call serial_putc
+    mov $disk_enum_msg, %si
+    call prints_number
 .disk_skip:
     decw disk_id
     jns .disk_enum
@@ -68,5 +62,8 @@ entry:
 .halt:
     jmp .halt
 
+.section .rodata
+disk_enum_msg:  .asciz  "Disk "
+
 .section .bss
-disk_id:   .word
+disk_id:        .word

src/util.s

@@ -0,0 +1,25 @@
+.section .text
+.code16
+
+.globl prints_number
+.globl empty_string
+
+# eax - number, ds:si - header string
+prints_number:
+    # header
+    push %eax
+    call prints
+    pop %eax
+
+    mov $10, %cx
+    call itoa
+    call prints
+
+    # newline
+    mov $'\n', %al
+    call serial_putc
+
+    ret
+
+.section .rodata
+empty_string: .byte 0