2 files changed, 58 insertions, 0 deletions
diff --git a/linux64/Makefile b/linux64/Makefile
new file mode 100644
index 0000000..5254a2f
--- /dev/null
+++ b/linux64/Makefile
@@ -0,0 +1,3 @@
+default:
+		nasm -f elf64 foo.asm
+		ld -o foo foo.o
diff --git a/linux64/foo.asm b/linux64/foo.asm
new file mode 100644
index 0000000..38dcca0
--- /dev/null
+++ b/linux64/foo.asm
@@ -0,0 +1,55 @@
+bits 64
+
+section .data
+	usage:		db 'usage: ', 0x00
+	params:		db ' [string]', 0x00
+	newline:	db 0x0a, 0x00
+
+section .text
+	global _start
+
+_start:
+	pop rax			; argc is on stack
+	cmp rax,1 		; see if is 1 (no parameters)
+	je help
+	pop rsi			; program name
+	pop rsi			; first parameter
+	call print
+	mov rsi, newline
+	call print
+	jmp exit
+
+help:
+	mov rsi, usage
+	call print
+	pop rsi
+	call print
+	mov rsi, params
+	call print
+	mov rsi, newline
+	call print
+
+	jmp exit
+
+print:
+	mov rdi, rsi		; copy, scasb uses edi
+	xor al, al		; al = 0
+	mov rcx, 4096		; maximum length 4096
+				; this is used by REPNE
+				; and not specific to SCASB
+	cld
+	repne scasb		; scan for '\0'
+				; edi is now address of '\0'
+	sub rdi, rsi		; rdi is now length of string
+	mov rdx, rdi		; rdx : write(..., strlen)
+	sub rdx, 1		; skip '\0'
+
+	mov rax, 1		; syscall  write()
+	mov rdi, 1		; rdi : write(fd, ...)
+	syscall
+	ret
+
+exit:
+	mov rax, 60		; exit()
+	mov rdi, 0
+	syscall