/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1991, 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/param.h>
#include <sys/mman.h>
#include <sys/stat.h>

#include <capsicum_helpers.h>
#include <err.h>
#include <limits.h>
#include <signal.h>
#include <stdbool.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>

#include "extern.h"

static u_char *remmap(u_char *, int, off_t);
static void segv_handler(int);
#define MMAP_CHUNK (8*1024*1024)

#define ROUNDPAGE(i) ((i) & ~pagemask)

int
c_regular(int fd1, const char *file1, off_t skip1, off_t len1,
    int fd2, const char *file2, off_t skip2, off_t len2, off_t limit)
{
        struct sigaction act, oact;
        cap_rights_t rights;
        u_char ch, *p1, *p2, *m1, *m2, *e1, *e2;
        off_t byte, length, line;
        off_t pagemask, off1, off2;
        size_t pagesize;
        int dfound;

        if (skip1 > len1) {
                eofmsg(file1);
                return (DIFF_EXIT);
        }
        len1 -= skip1;
        if (skip2 > len2) {
                eofmsg(file2);
                return (DIFF_EXIT);
        }
        len2 -= skip2;

        if (sflag && len1 != len2)
                return (DIFF_EXIT);

        pagesize = getpagesize();
        pagemask = (off_t)pagesize - 1;
        off1 = ROUNDPAGE(skip1);
        off2 = ROUNDPAGE(skip2);

        length = MIN(len1, len2);
        if (limit > 0)
                length = MIN(length, limit);

        if ((m1 = remmap(NULL, fd1, off1)) == NULL) {
                return (c_special(fd1, file1, skip1, fd2, file2, skip2, limit));
        }

        if ((m2 = remmap(NULL, fd2, off2)) == NULL) {
                munmap(m1, MMAP_CHUNK);
                return (c_special(fd1, file1, skip1, fd2, file2, skip2, limit));
        }

        if (caph_rights_limit(fd1, cap_rights_init(&rights, CAP_MMAP_R)) < 0)
                err(1, "unable to limit rights for %s", file1);
        if (caph_rights_limit(fd2, cap_rights_init(&rights, CAP_MMAP_R)) < 0)
                err(1, "unable to limit rights for %s", file2);
        if (caph_enter() < 0)
                err(ERR_EXIT, "unable to enter capability mode");

        sigemptyset(&act.sa_mask);
        act.sa_flags = SA_NODEFER;
        act.sa_handler = segv_handler;
        if (sigaction(SIGSEGV, &act, &oact))
                err(ERR_EXIT, "sigaction()");

        dfound = 0;
        e1 = m1 + MMAP_CHUNK;
        e2 = m2 + MMAP_CHUNK;
        p1 = m1 + (skip1 - off1);
        p2 = m2 + (skip2 - off2);

        for (byte = line = 1; length--; ++byte) {
#ifdef SIGINFO
                if (info) {
                        (void)fprintf(stderr, "%s %s char %zu line %zu\n",
                            file1, file2, (size_t)byte, (size_t)line);
                        info = 0;
                }
#endif
                if ((ch = *p1) != *p2) {
                        dfound = 1;
                        if (xflag) {
                                (void)printf("%08llx %02x %02x\n",
                                    (long long)byte - 1, ch, *p2);
                        } else if (lflag) {
                                if (bflag)
                                        (void)printf("%6lld %3o %c %3o %c\n",
                                            (long long)byte, ch, ch, *p2, *p2);
                                else
                                        (void)printf("%6lld %3o %3o\n",
                                            (long long)byte, ch, *p2);
                        } else {
                                diffmsg(file1, file2, byte, line, ch, *p2);
                                return (DIFF_EXIT);
                        }
                }
                if (ch == '\n')
                        ++line;
                if (++p1 == e1) {
                        off1 += MMAP_CHUNK;
                        if ((p1 = m1 = remmap(m1, fd1, off1)) == NULL) {
                                munmap(m2, MMAP_CHUNK);
                                err(ERR_EXIT, "remmap %s", file1);
                        }
                        e1 = m1 + MMAP_CHUNK;
                }
                if (++p2 == e2) {
                        off2 += MMAP_CHUNK;
                        if ((p2 = m2 = remmap(m2, fd2, off2)) == NULL) {
                                munmap(m1, MMAP_CHUNK);
                                err(ERR_EXIT, "remmap %s", file2);
                        }
                        e2 = m2 + MMAP_CHUNK;
                }
        }
        munmap(m1, MMAP_CHUNK);
        munmap(m2, MMAP_CHUNK);

        if (sigaction(SIGSEGV, &oact, NULL))
                err(ERR_EXIT, "sigaction()");

        if (len1 != len2) {
                eofmsg(len1 > len2 ? file2 : file1);
                return (DIFF_EXIT);
        }
        return (dfound ? DIFF_EXIT : 0);
}

static u_char *
remmap(u_char *mem, int fd, off_t offset)
{
        if (mem != NULL)
                munmap(mem, MMAP_CHUNK);
        mem = mmap(NULL, MMAP_CHUNK, PROT_READ, MAP_SHARED, fd, offset);
        if (mem == MAP_FAILED)
                return (NULL);
        madvise(mem, MMAP_CHUNK, MADV_SEQUENTIAL);
        return (mem);
}

static void
segv_handler(int sig __unused) {
        static const char msg[] = "cmp: Input/output error (caught SIGSEGV)\n";

        write(STDERR_FILENO, msg, sizeof(msg));
        _exit(EXIT_FAILURE);
}