External include files

Makefile

@@ -1,6 +1,7 @@
 .PHONY: all clean
 
 SRC := $(wildcard *.asm)
+SRC := $(filter-out functions.asm, $(SRC))
 OBJDIR := build
 OBJS := $(SRC:%.asm=$(OBJDIR)/%.o)
 BINS := $(SRC:%.asm=$(OBJDIR)/%)

README.md

@@ -1,3 +1,3 @@
 # asm
 
-Build x86_64 assembly examples from [asmtutor.com](https://asmtutor.com)
+x86 assembly exercises using [asmtutor.com](https://asmtutor.com)

functions.asm

@@ -0,0 +1,39 @@
+SYS_EXIT    equ 1
+SYS_WRITE   equ 4
+STDOUT      equ 1
+
+strlen:
+    push    ebx
+    mov     ebx, eax
+nextchar:
+    cmp     byte[eax], 0
+    jz      finished
+    inc     eax
+    jmp     nextchar
+finished:
+    sub     eax, ebx
+    pop     ebx
+    ret
+
+print:
+    push    ebx
+    push    ecx
+    push    edx
+
+    mov     ebx, eax
+    call    strlen
+    mov     edx, eax
+    mov     ecx, ebx
+    mov     ebx, STDOUT
+    mov     eax, SYS_WRITE
+    int     0x80
+
+    pop     edx
+    pop     ecx
+    pop     ebx
+    ret
+
+quit:
+    mov     ebx, 0
+    mov     eax, SYS_EXIT
+    int     0x80

helloworld.asm

@@ -1,39 +1,15 @@
-; Hello World Program - asmtutor.com
+%include        'functions.asm'
-; Compile with: nasm -f elf helloworld.asm
-; Link with (64 bit systems require elf_i386 option): ld -m elf_i386 helloworld.o -o helloworld
-; Run with: ./helloworld
 
-SECTION .data
+section .data
-msg     db      'Hello, brave new world!', 0Ah     ; assign msg variable with your message string
+msg1     db      "Hello, world!", 0Ah
+msg2     db      "Display a line of text", 0Ah
 
-SECTION .text
+section .text
-global  _start
+global _start
 
 _start:
-    mov     eax, msg
+    mov     eax, msg1
-    call    strlen
+    call    print
-
+    mov     eax, msg2
-    mov     edx, eax        ; our function leaves the result in EAX
+    call    print
-    mov     ecx, msg
+    call    quit
-    mov     ebx, 1          ; STDOUT
-    mov     eax, 4          ; SYS_WRITE
-    int     80h
-
-    mov     ebx, 0          ; return 0
-    mov     eax, 1          ; SYS_EXIT
-    int     80h
-
-strlen:
-    push    ebx             ; preserve EBX while we use in this function
-    mov     ebx, eax        ; move the address in EAX into EBX
-
-nextchar:
-    cmp     byte [eax], 0   ; compare the byte pointed to by EAX at this address against zero (Zero is an end of string delimiter)
-    jz      finished        ; jump (if the zero flagged has been set) to the point in the code labeled 'finished'
-    inc     eax             ; increment the address in EAX by one byte (if the zero flagged has NOT been set)
-    jmp     nextchar        ; jump to the point in the code labeled 'nextchar'
-
-finished:
-    sub     eax, ebx
-    pop     ebx
-    ret