Argument parsing code enhancement

Using call & ret (but that's maybe not necessary...)
Reducing instruction size

wtfstopw.asm

 _start:
 
 ; parse arguments and set time_res value
-jmp arg_parse
-arg_ok:
+call arg_parse
 
 mov rbx, ts_start
 %define RBXPTR(x) rbx + x - ts_start
 ;
 arg_parse:
 	; Checking argument count
-	mov rax, [rsp]
-	cmp rax, 1
+	mov rcx, [rsp+8] ; argc
+	mov rsi, [rsp+24] ; argv[1]
+	mov rdi, badarg_msg
+
+	cmp rcx, 1
 	je arg_ok
-	cmp rax, 3
+	cmp rcx, 3
 	jle parse_r
 	arg_err: ; badval & badarg jmp here too
-		mov rax, [rsp+8] ; argv[0] program name
+		mov rax, [rsp+16] ; argv[0] program name
 		mov rdi, -1 ; return status
 		jmp usage
 	parse_r:
-	mov rax, [rsp+16] ; 1st arg should be "-r"
-	mov bl, [rax]
-	cmp bl, '-'
+	mov rax, rsi
+	cmp byte [rsi], '-'
 	jne badarg
-	mov bl, [rax+1]
+	mov bl, [rsi+1]
 	cmp bl, 'h' ; -h
 	je arg_err
 	cmp bl, 'r'
 	jne badarg
-	mov bl, [rax+2]
-	cmp bl, 0
+	cmp byte [rsi+2], 0
 	jne arg_nxt ; the value seems to be just after the -r like -r2
 	nxt_arg:
 		; the 1st argument is -r the second must be the time_res
 		; check that the arg exists
-		mov rax, [rsp]
-		cmp rax, 3
+		cmp cl, 3
 		jne arg_err
-		mov rax, [rsp+24]
+		mov rsi, [rsp+32]
 		jmp arg_cont
 	arg_nxt:
 		; check that there is no more args
-		mov rbx, [rsp]
-		cmp rbx, 2
+		cmp cl, 2
 		jne arg_err
-		add rax, 2
+		add rsi, 2
 	arg_cont:
-	; rax should point on the value
-	mov bl, [rax+1]
-	cmp bl, 0
+	; rsi should point on the ASCII digit counter
+	cmp byte [rsi+1], 0
 	jne badval
 	xor rbx, rbx
-	mov bl, [rax]
+	mov bl, [rsi]
 	cmp bl, '1'
 	jl badval
 	cmp bl, '8'
 	jg badval
-	sub bl, '0'
-	mov [time_res], rbx
-	jmp arg_ok
+	xor bl, 0x30 ; '0'
+	mov [rdi + time_res - badarg_msg], rbx
+
+	arg_ok:
+	ret
 
-; print an error message, usage and exit with rax pointing the value
+; print an error message, usage and exit with rax pointing the value and
+; rdi badarg_msg ptr
 badval:
-	mov rsi, badval_msg
+	mov rbx, rsi
+
+	lea rsi, [rdi + badval_msg - badarg_msg]
 	mov rdx, badval_msglen
 	jmp arg_strerr
 
 ; print an error message, usage and exit
 badarg:
-	mov rsi, badarg_msg
+	mov rbx, rsi
+	mov rsi, rdi
 	mov rdx, badarg_msglen
-	mov rax, [rsp+16]
 	jmp arg_strerr
 
-; rsi msg ptr, rdx msg len, rax arg ptr
+; rsi msg ptr, rdx msg len, rbx arg ptr
 arg_strerr:
-	mov r8, rax
 	mov rax, 1
 	mov rdi, 1
 	syscall
-	mov rsi, r8
-	mov rax, r8
+	mov rsi, rbx
+	mov rax, rbx
 	call proc_strlen
 	mov rax, 1
 	syscall