build.c

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/*
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *  Copyright (C) 1997 Martin Mares
 */

/*
 * This file builds a disk-image from three different files:
 *
 * - bootsect: exactly 512 bytes of 8086 machine code, loads the rest
 * - setup: 8086 machine code, sets up system parm
 * - system: 80386 code for actual system
 *
 * It does some checking that all files are of the correct type, and
 * just writes the result to stdout, removing headers and padding to
 * the right amount. It also writes some system data to stderr.
 */

/*
 * Changes by tytso to allow root device specification
 * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
 * Cross compiling fixes by Gertjan van Wingerde, July 1996
 * Rewritten by Martin Mares, April 1997
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdarg.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
#include <unistd.h>
#include <fcntl.h>
#include <asm/boot.h>

#define DEFAULT_MAJOR_ROOT 0
#define DEFAULT_MINOR_ROOT 0

/* Minimal number of setup sectors (see also bootsect.S) */
#define SETUP_SECTS 4

uint8_t buf[1024];
int fd;
int is_big_kernel;

__attribute__((noreturn))
void die(const char *str, ...)
{
    va_list args;
    va_start(args, str);
    vfprintf(stderr, str, args);
    fputc('\n', stderr);
    exit(1);
}

void file_open(const char *name)
{
    fd = open(name, O_RDONLY, 0);
    if (fd < 0)
        die("Unable to open `%s': %m", name);
}

__attribute__((noreturn))
void usage(void)
{
    die("Usage: build [-b] bootsect setup system [rootdev] [> image]");
}

int main(int argc, char **argv)
{
    unsigned int i, c, sz, setup_sectors;
    uint32_t sys_size;
    uint8_t major_root, minor_root;
    struct stat sb;

    if (argc > 2 && !strcmp(argv[1], "-b")) {
        is_big_kernel = 1;
        argc--, argv++;
    }
    if ((argc < 4) || (argc > 5))
        usage();
    if (argc > 4) {
        if (!strcmp(argv[4], "CURRENT")) {
            if (stat("/", &sb)) {
                perror("/");
                die("Couldn't stat /");
            }
            major_root = major(sb.st_dev);
            minor_root = minor(sb.st_dev);
        } else if (strcmp(argv[4], "FLOPPY")) {
            if (stat(argv[4], &sb)) {
                perror(argv[4]);
                die("Couldn't stat root device.");
            }
            major_root = major(sb.st_rdev);
            minor_root = minor(sb.st_rdev);
        } else {
            major_root = 0;
            minor_root = 0;
        }
    } else {
        major_root = DEFAULT_MAJOR_ROOT;
        minor_root = DEFAULT_MINOR_ROOT;
    }
    fprintf(stderr, "Root device is (%d, %d)\n", major_root, minor_root);

    file_open(argv[1]);
    i = read(fd, buf, sizeof(buf));
    fprintf(stderr, "Boot sector %d bytes.\n", i);
    if (i != 512)
        die("Boot block must be exactly 512 bytes");
    if (buf[510] != 0x55 || buf[511] != 0xaa)
        die("Boot block hasn't got boot flag (0xAA55)");
    buf[508] = minor_root;
    buf[509] = major_root;
    if (write(1, buf, 512) != 512)
        die("Write call failed");
    close(fd);

    /* Copy the setup code */
    file_open(argv[2]);
    for (i = 0; (c = read(fd, buf, sizeof(buf))) > 0; i += c)
        if (write(1, buf, c) != c)
            die("Write call failed");
    if (c != 0)
        die("read-error on `setup'");
    close(fd);

    /* Pad unused space with zeros */
    setup_sectors = (i + 511) / 512;
    /* for compatibility with ancient versions of LILO. */
    if (setup_sectors < SETUP_SECTS)
        setup_sectors = SETUP_SECTS;
    fprintf(stderr, "Setup is %d bytes.\n", i);
    memset(buf, 0, sizeof(buf));
    while (i < setup_sectors * 512) {
        c = setup_sectors * 512 - i;
        if (c > sizeof(buf))
            c = sizeof(buf);
        if (write(1, buf, c) != c)
            die("Write call failed");
        i += c;
    }

    file_open(argv[3]);
    if (fstat(fd, &sb))
        die("Unable to stat `%s': %m", argv[3]);
    sz = sb.st_size;
    fprintf(stderr, "System is %d kB\n", sz / 1024);
    sys_size = (sz + 15) / 16;
    /* 0x28000*16 = 2.5 MB, conservative estimate for the current maximum */
    if (sys_size > (is_big_kernel ? 0x28000 : DEF_SYSSIZE))
        die("System is too big. Try using %smodules.",
            is_big_kernel ? "" : "bzImage or ");
    if (sys_size > 0xffff)
        fprintf(stderr,
            "warning: kernel is too big for standalone boot "
            "from floppy\n");
    while (sz > 0) {
        int l, n;

        l = (sz > sizeof(buf)) ? sizeof(buf) : sz;
        n = read(fd, buf, l);
        if (n != l) {
            if (n < 0)
                die("Error reading %s: %m", argv[3]);
            else
                die("%s: Unexpected EOF", argv[3]);
        }
        if (write(1, buf, l) != l)
            die("Write failed");
        sz -= l;
    }
    close(fd);

    /* Write sizes to the bootsector */
    if (lseek(1, 497, SEEK_SET) != 497)
        die("Output: seek failed");
    buf[0] = setup_sectors;
    if (write(1, buf, 1) != 1)
        die("Write of setup sector count failed");
    if (lseek(1, 500, SEEK_SET) != 500)
        die("Output: seek failed");
    buf[0] = (sys_size & 0xff);
    buf[1] = ((sys_size >> 8) & 0xff);
    if (write(1, buf, 2) != 2)
        die("Write of image length failed");

    return 0;
}