added macro and function def/call to x64

diff --git a/hello64.asm b/hello64.asm
index 32296f5..1d57033 100644 (file)
--- a/hello64.asm
+++ b/hello64.asm
@@ -1,27 +1,38 @@
+%macro print 2           ; Declare a macro to print a string, with two arguments
+    mov rax,1            ; Put magic # for system call sys_write into rax
+    mov rdi,1            ; Prepare arg 1 of sys_write, 1 - file descriptor of stdo
+    mov rsi,%1           ; Prepare arg 2, a string reference
+    mov rdx,%2           ; Prepare arg 3, string length, no deref. b/c constant 
+    syscall              ; Call the kernel
+%endmacro
+
 section .data
-    hello:     db 'Hello, world.',10   ; declare initialized string with linefeed char
-    helloLen:  equ $-hello             ; declare and init. constant
-    done: db 0
+    hello:     db  'Hello, world.',10   ; declare initialized string with linefeed char
+    helloLen:  equ $-hello              ; declare and init. constant
+    done:      db  0
 
 section .text
-    global _start
+    global _start        ; Declare program entry point
+
+_print:
+    push rbp             ; Prologue, save stack pointer
+    mov rbp,rsp          ; Get base pointer (start of arguments)
+    mov rbx,[rbp+16]     ; Get first argument (offset from base by the return address)
+    print rbx,helloLen   ; Macro, replaced inline
+    leave                ; Epilogue, equivalent to mov rsp,rbp; pop rbp
+    ret                  ; Return control to caller
 
 _start:
-    movzx rax, byte [done]      ; Pad value of done to one byte and put in rax
-    cmp rax,1                   ; Compare rax with 1
-    jg myFirstASMLabel          ; Jump if greater than to myFirstASMLabel
+    cmp byte [done],1    ; Compare byte padded value of done with 1
+    jg exit              ; Jump if greater than to exit
 
-    mov byte [done], 1
+    mov byte [done], 1   ; Put 1 in done
 
-    mov rax,1            ; Put magic # for system call sys_write into rax
-    mov rdi,1            ; Prepare arg 1 of sys_write, 1 - file descriptor of stdo
-    mov rsi,hello        ; Prepare arg 2, reference to string hello
-    mov rdx,helloLen     ; Prepare arg 3, string length, no deref. b/c constant 
-    syscall              ; Call the kernel
-;
+    push hello           ; Push the last argument of _print onto the stack
+    call _print          ; Call the function _print
 
-myFirstASMLabel:
-    mov rax,60            ; The system call for exit (sys_exit)
-    mov rdi,0             ; Exit with return code of 0 (no error)
+exit:
+    mov rax,60           ; The system call for exit (sys_exit)
+    mov rdi,0            ; Exit with return code of 0 (no error)
     syscall