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build.c

/*
 *  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;
}

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