Start writing file functions

src/file.asm

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+%include "src/constants.asm"
+
+extern	umask_get
+
+section .rodata
+	; Open flags
+	O_ACCMODE	equ	00000003
+	O_RDONLY	equ	00000000	
+	O_WRONLY	equ	00000001
+	O_RDWR		equ	00000002
+	O_CREAT		equ	00000100 ;create if not exist
+	O_EXCL		equ	00000200 ;fail if file exists and O_EXCL+O_CREAT set
+	O_NOCTTY	equ	00000400 
+	O_TRUNC		equ	00001000 
+	O_APPEND	equ	00002000
+	O_NONBLOCK	equ	00004000
+	O_DSYNC		equ	00010000
+	FASYNC		equ	00020000
+	O_DIRECT	equ	00040000
+	O_LARGEFILE	equ	00100000
+	O_DIRECTORY	equ	00200000
+	O_NOFOLLOW	equ	00400000
+	O_NOATIME	equ	01000000
+	O_CLOEXEC	equ	02000000
+	__O_SYNC	equ	04000000
+	O_SYNC		equ	(__O_SYNC | O_DSYNC)
+	O_PATH		equ	01000000
+	__O_TMPFILE	equ	02000000
+	O_TMPFILE	equ	(__O_TMPFILE | O_DIRECTORY)
+	O_NDELAY	equ	O_NONBLOCK
+	; Permission flags
+	S_IXOTH		equ	00001 ;o=x
+	S_IWOTH		equ	00002 ;o=w
+	S_IROTH		equ	00004 ;o=r
+	S_IRWXO		equ	00007 ;o=rwx
+	S_IXGRP		equ	00010 ;g=x
+	S_IWGRP		equ	00020 ;g=w
+	S_IRGRP		equ	00040 ;g=r
+	S_IRWXG		equ	00070 ;g=rwx
+	S_IXUSR		equ	00100 ;u=x
+	S_IWUSR		equ	00200 ;u=w
+	S_IRUSR		equ	00400 ;u=r
+	S_IRWXU		equ	00700 ;u=rwx
+	S_ISVIX		equ	0001000 ;sticky bit
+	S_ISGID		equ	0002000 ;set-group-ID bit
+	S_ISUID		equ	0004000 ;set-user-ID bit	
+
+section .bss
+
+section .text
+	global	fopen
+	global	fclose
+	global	fexist
+
+;----- fopen(*file[], char mode) -----;
+; Opens a file
+; Return value: Pointer to opened file pointer, 0 (EOS) otherwise.
+; Possible modes:
+;	'r'	Read-only, file must exist
+;	'w'	Write-only. Creates empty file or truncates an existing file
+;	'a'	Append. Creates file if it does not exist
+;	'R'	Read+write, file must exist
+;	'W'	Read+write. Creates empty file or truncates an existing file
+;	'A'	Read+append. Creates file if it does not exist
+;	<!>	Invalid mode will also return 0 (EOS)
+; Used registers:
+;	rax*	(ret)
+;	rdi	(arg) Pointer to string holding (path+)file name
+;	rsi	Mode to open the file with (see description above)
+fopen:
+	ret
+
+;----- fclose(file) -----;
+; Closes an opened file
+; Return value: 0 if file closed. Negative error number if an error occured
+; Used registers:
+;	rax*	(ret)
+;	rdi	(arg) Pointer to opened file
+fclose:
+	cmp	rdi, 3
+	jl	.invalid_fd ;disallow closing stdin,stdout,stderr
+	mov	rax, NR_close
+	syscall
+	jmp	.quit
+
+	.invalid_fd:
+	mov	rax, -EINVAL
+
+	.quit:
+	ret
+
+;----- fexist(*file[]) -----;
+; Checks if given file exists (attempts to open the file)
+; Return value: 0- File closed succesfully. -errno (negative error number) if an error occured
+; Used registers:
+;	rax*	(ret)
+;	rdi	(arg) Pointer to string holding (path+)file name
+fexist:
+	ret