Add hello-world

hello-world/hello.s

@@ -0,0 +1,27 @@
+# PURPOSE: Print "Hello, World!", then exit.
+# INPUT: None.
+# OUTPUT:    Prints a string to stdout.
+#           Returns a status code of 0.
+# VARIABLES:
+#           %rax holds the system call number
+#           %rbx holds the return status
+.section .data
+hw:
+        .ascii "Hello, World!"
+
+.section .text
+        .globl _start
+
+_exit:
+        mov $1, %rax # System call number for exit.
+        mov $0, %rbx # Exit code.
+        int $0x80    # Call the kernel.
+
+_start:
+        mov $4, %rax  # System call number for write.
+        mov $1, %rbx  # stdout.
+        mov $hw, %rcx # Address of the buffer.
+        mov $15, %rdx # Number of bytes to write.
+        int $0x80     # Call the kernel.
+
+call _exit # Call the _exit macro.