Merge pull request #5 from Sumukha87/main-1

Create helloWorld.asm

helloWorld.asm

@@ -0,0 +1,46 @@
+; Prints "hello world" to the screen. 
+; OS/X requires system call arguments to be pushed onto the stack in reversed 
+; order, with an extra 4 bytes (DWORD) at the end. 
+;
+; Build with: 
+;   nasm -f macho hello.asm
+;   ld -o hello hello.o
+;
+; Run with: 
+;   ./hello
+;
+; Author: Sumukha87
+
+
+
+SECTION .data           ; initialised data section
+
+Msg: db "hello world", 10           ; message to print
+MsgLen: equ $ - Msg                 ; length of message
+
+
+SECTION .text           ; code section
+
+global start
+start:
+
+    ; printing message, use write()
+    ; system call 4 syntax: 
+    ; user_ssize_t write(int fd, user_addr_t cbuf, user_size_t nbyte)
+    push dword MsgLen   ; length of message to print
+    push dword Msg      ; message to print
+    push dword 1        ; FD of 1 for standard output
+    sub esp, 4          ; OS/X requires extra 4 bytes after arguments
+    mov eax, 4          ; 4 - write() system call
+    int 80H             ; perform system call
+    add esp, 16         ; restore stack (16 bytes pushed: 3 * dword + 4)
+
+    ; program exit, use sys_exit()
+    push dword 0        ; exit value of 0 returned to the OS
+    sub esp, 4          ; OS/X requires extra 4 bytes after arguments
+    mov eax, 1          ; 1 - sys_exit() system call
+    int 80H             ; perform system call
+    ; no need to restore stack, code after this line will not be executed 
+    ; (program exit)
+
+@Sumukha87