; syscall0s_64.asm   demonstrate operating system kernel calls
; Compile:	nasm -f elf64 syscall0s_64.asm
; Link		ld -m64 -o syscall0s_64 syscall0s_64.o
; Run:		./syscall0s_64
;

	section	.data
msg:	db  "syscall0s_64.asm running",10	; the string to print, 10=crlf
len:	equ $-msg     ; "$" means here, len is a value, not an address
msg2:	db  "syscall0s_64.asm finished",10 	; no 0 needed
len2:	equ $-msg2
msg3:	db  "syscall0s_64.asm opened",10
len3:	equ $-msg3
msg4:	db  "syscall0s_64.asm read",10
len4:	equ $-msg4
msg5:	db  "syscall0s_64.asm open fail",10
len5:	equ $-msg5
msg6:	db  "syscall0s_64.asm another open fail",10
len6:	equ $-msg6
msg7:	db  "syscall0s_64.asm read fail",10
len7:	equ $-msg7

name:	db  "syscall0s_64.asm",0 	; "C" string, zero needed
fd:	dq  0			; file descriptor, int
flags:	dq  0			; hopefully read-only
	section .bss
line:	resb  8193		; read/write buffer 16 sectors of 512
lenbuf:	resq     1		; number of bytes read

	extern  open
	global	_start
	section .text
_start:

; header msg			; these 5 lines are like  printf
	mov	rdx,len		; arg3, length of string to print
	mov	rcx,msg		; arg2, pointer to string
	mov	rbx,1		; arg1, where to write, screen
	mov	rax,4		; write command to int 80 hex
	int	0x80		; interrupt 80 hex, call kernel


	
	mov	rbx,0		; exit code, 0=normal
	mov	rax,1		; exit command to kernel
	int	0x80		; interrupt 80 hex, call kernel