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For open/openat, if the flags parameter does not contain O_CREAT, the
3rd (variadic) mode_t parameter is irrelevant.  Many developers in the past
have passed mode_t (0, 044, 0644, or such), which might lead future people
to copy this broken idiom, and perhaps even believe this parameter has some
meaning or implication or application. Delete them all.
This comes out of a conversation where tb@ noticed that a strange (but
intentional) pledge behaviour is to always knock-out high-bits from
mode_t on a number of system calls as a safety factor, and his bewilderment
that this appeared to be happening against valid modes (at least visually),
but no sorry, they are all irrelevant junk.  They could all be 0xdeafbeef.
ok millert

/*      $OpenBSD: cmp.c,v 1.19 2021/10/24 21:24:16 deraadt Exp $      */
/*      $NetBSD: cmp.c,v 1.7 1995/09/08 03:22:56 tls Exp $      */

/*
 * Copyright (c) 1987, 1990, 1993, 1994
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/types.h>
#include <sys/stat.h>

#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "extern.h"

int	lflag, sflag;

static off_t get_skip(const char *, const char *);
static void __dead usage(void);

int
main(int argc, char *argv[])
{
	struct stat sb1, sb2;
	off_t skip1, skip2;
	int ch, fd1, fd2, special;
	char *file1, *file2;

	if (pledge("stdio rpath", NULL) == -1)
		err(ERR_EXIT, "pledge");

	while ((ch = getopt(argc, argv, "ls")) != -1)
		switch (ch) {
		case 'l':		/* print all differences */
			lflag = 1;
			break;
		case 's':		/* silent run */
			sflag = 1;
			break;
		default:
			usage();
		}

	argv += optind;
	argc -= optind;

	if (lflag && sflag)
		errx(ERR_EXIT, "only one of -l and -s may be specified");

	if (argc < 2 || argc > 4)
		usage();

	/* Backward compatibility -- handle "-" meaning stdin. */
	special = 0;
	if (strcmp(file1 = argv[0], "-") == 0) {
		special = 1;
		fd1 = 0;
		file1 = "stdin";
	} else if ((fd1 = open(file1, O_RDONLY)) == -1)
		fatal("%s", file1);
	if (strcmp(file2 = argv[1], "-") == 0) {
		if (special)
			fatalx("standard input may only be specified once");
		special = 1;
		fd2 = 0;
		file2 = "stdin";
	} else if ((fd2 = open(file2, O_RDONLY)) == -1)
		fatal("%s", file2);

	if (pledge("stdio", NULL) == -1)
		err(ERR_EXIT, "pledge");

	skip1 = (argc > 2) ? get_skip(argv[2], "skip1") : 0;
	skip2 = (argc == 4) ? get_skip(argv[3], "skip2") : 0;

	if (!special) {
		if (fstat(fd1, &sb1) == -1)
			fatal("%s", file1);
		if (!S_ISREG(sb1.st_mode))
			special = 1;
		else {
			if (fstat(fd2, &sb2) == -1)
				fatal("%s", file2);
			if (!S_ISREG(sb2.st_mode))
				special = 1;
		}
	}

	if (special)
		c_special(fd1, file1, skip1, fd2, file2, skip2);
	else
		c_regular(fd1, file1, skip1, sb1.st_size,
		    fd2, file2, skip2, sb2.st_size);
	return 0;
}

static off_t
get_skip(const char *arg, const char *name)
{
	off_t skip;
	char *ep;

	errno = 0;
	skip = strtoll(arg, &ep, 0);
	if (arg[0] == '\0' || *ep != '\0')
		fatalx("%s is invalid: %s", name, arg);
	if (skip < 0)
		fatalx("%s is too small: %s", name, arg);
	if (skip == LLONG_MAX && errno == ERANGE)
		fatalx("%s is too large: %s", name, arg);
	return skip;
}

static void __dead
usage(void)
{

	(void)fprintf(stderr,
	    "usage: cmp [-l | -s] file1 file2 [skip1 [skip2]]\n");
	exit(ERR_EXIT);
}