Implement line reading

postfix.s

@@ -1,7 +1,32 @@
 	.text
 	.global _start
 _start:
+	mov $buf, %rsi
+readloop:
+	## Read character in.
+	mov $0, %rax
+	mov $0, %rdi
+	mov $1, %rdx
+	syscall
+
+	## Check return value; exit if not equal to one.
+	cmp $1, %rax
+	jne exit
+
+	## Move read character into RAX and increment buffer position.
+	movzx (%rsi), %rax
+	inc %rsi
+
+	## Loop if read character wasn't a line feed.
+	cmp $0x0a, %rax
+	jne readloop
+
+exit:
 	## Exit with code 0
 	mov $60, %rax
 	mov $0, %rdi
 	syscall
+
+	.bss
+buf:
+	.skip 100