Adds fopen(), fwrite(), fclose()

file.asm

@@ -0,0 +1,110 @@
+extern	NR_read
+extern	NR_write
+extern	NR_open
+extern	NR_close
+
+extern	strlen
+
+section .rodata
+	O_RDONLY	equ	00000000q
+	O_WRONLY	equ	00000001q
+	O_RDWR		equ	00000002q
+	O_CREAT		equ	00000100q
+	O_TRUNC		equ	00001000q
+	O_APPEND	equ	00002000q
+	
+section .text
+	global	fopen
+	global	fclose
+	global	fwrite
+
+;----- fopen(const char *filename, const char *mode) -----;
+; return value: pointer to file or NULL if file failed to open
+;              ┌─────────────┬───────────────────────────────┐
+;              │fopen() mode │ open() flags                  │
+;              ├─────────────┼───────────────────────────────┤
+;              │     r       │ O_RDONLY                      │
+;              ├─────────────┼───────────────────────────────┤
+;              │     w       │ O_WRONLY | O_CREAT | O_TRUNC  │
+;              ├─────────────┼───────────────────────────────┤
+;              │     a       │ O_WRONLY | O_CREAT | O_APPEND │
+;              ├─────────────┼───────────────────────────────┤
+;              │     R       │ O_RDWR                        │
+;              ├─────────────┼───────────────────────────────┤
+;              │     W       │ O_RDWR | O_CREAT | O_TRUNC    │
+;              ├─────────────┼───────────────────────────────┤
+;              │     A       │ O_RDWR | O_CREAT | O_APPEND   │
+;              └─────────────┴───────────────────────────────┘
+fopen:
+	push	rbp
+	mov	rbp, rsp
+
+	cmp	byte [rsi], 'r'
+	je	.setMode_r
+	cmp	byte [rsi], 'w'
+	je	.setMode_w
+	cmp	byte [rsi], 'a'
+	je	.setMode_a
+	cmp	byte [rsi], 'R'
+	je	.setMode_R
+	cmp	byte [rsi], 'W'
+	je	.setMode_W
+	cmp	byte [rsi], 'A'
+	je	.setMode_A
+	xor	rax, rax
+	jmp	.quit
+
+	.setMode_r:
+		mov	rsi, O_RDONLY
+		jmp	.open
+	.setMode_w:
+		mov	rsi, O_WRONLY | O_CREAT | O_TRUNC
+		jmp	.open
+	.setMode_a:
+		mov	rsi, O_WRONLY | O_CREAT | O_APPEND
+		jmp	.open
+	.setMode_R:
+		mov	rsi, O_RDWR
+		jmp	.open
+	.setMode_W:
+		mov	rsi, O_RDWR | O_CREAT | O_TRUNC
+		jmp	.open
+	.setMode_A:
+		mov	rsi, O_RDWR | O_CREAT | O_APPEND
+		jmp	.open
+
+	.open:
+	mov	rax, NR_open
+	syscall
+
+	.quit:
+	leave
+	ret
+;----- fclose(FILE* fp) -----;
+; return value: 0 on success, below 0 otherwise
+fclose:
+	push	rbp
+	mov	rbp, rsp
+
+	mov	rax, NR_close
+	syscall
+
+	leave
+	ret
+;----- fwrite(FILE* fp, char* str) -----;
+; writes a string to opened file
+; return value: 0 on success, below 0 otherwise
+fwrite:
+	push	rbp
+	mov	rbp, rsp
+
+	mov	r9, rdi
+	mov	rdi, rsi
+	call	strlen
+	mov	rdx, rax
+	mov	rax, NR_write
+	mov	rdi, r9
+	syscall
+
+	leave
+	ret