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;
}