piggyback.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
   Simple utility to make a single-image install kernel with initial ramdisk
   for Sparc tftpbooting without need to set up nfs.

   Copyright (C) 1996,1997 Jakub Jelinek ([email protected])
   Pete Zaitcev <[email protected]> endian fixes for cross-compiles, 2000.
   Copyright (C) 2011 Sam Ravnborg <[email protected]>

 */

#include <dirent.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>

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

/*
 * Note: run this on an a.out kernel (use elftoaout for it),
 * as PROM looks for a.out image only.
 */

#define AOUT_TEXT_OFFSET   32

static int is64bit = 0;

/* align to power-of-two size */
static int align(int n)
{
	if (is64bit)
		return (n + 0x1fff) & ~0x1fff;
	else
		return (n + 0xfff) & ~0xfff;
}

/* read two bytes as big endian */
static unsigned short ld2(char *p)
{
	return (p[0] << 8) | p[1];
}

/* save 4 bytes as big endian */
static void st4(char *p, unsigned int x)
{
	p[0] = x >> 24;
	p[1] = x >> 16;
	p[2] = x >> 8;
	p[3] = x;
}

static void die(const char *str)
{
	perror(str);
	exit(1);
}

static void usage(void)
{
	/* fs_img.gz is an image of initial ramdisk. */
	fprintf(stderr, "Usage: piggyback bits vmlinux.aout System.map fs_img.gz\n");
	fprintf(stderr, "\tKernel image will be modified in place.\n");
	exit(1);
}

static int start_line(const char *line)
{
	if (strcmp(line + 10, " _start\n") == 0)
		return 1;
	else if (strcmp(line + 18, " _start\n") == 0)
		return 1;
	return 0;
}

static int end_line(const char *line)
{
	if (strcmp(line + 10, " _end\n") == 0)
		return 1;
	else if (strcmp (line + 18, " _end\n") == 0)
		return 1;
	return 0;
}

/*
 * Find address for start and end in System.map.
 * The file looks like this:
 * f0004000 ... _start
 * f0379f79 ... _end
 * 1234567890123456
 * ^coloumn 1
 * There is support for 64 bit addresses too.
 *
 * Return 0 if either start or end is not found
 */
static int get_start_end(const char *filename, unsigned int *start,
                                               unsigned int *end)
{
	FILE *map;
	char buffer[1024];

	*start = 0;
	*end = 0;
	map = fopen(filename, "r");
	if (!map)
		die(filename);
	while (fgets(buffer, 1024, map)) {
		if (start_line(buffer))
			*start = strtoul(buffer, NULL, 16);
		else if (end_line(buffer))
			*end = strtoul(buffer, NULL, 16);
	}
	fclose (map);

	if (*start == 0 || *end == 0)
		return 0;

	return 1;
}

#define LOOKBACK (128 * 4)
#define BUFSIZE 1024
/*
 * Find the HdrS entry from head_32/head_64.
 * We check if it is at the beginning of the file (sparc64 case)
 * and if not we search for it.
 * When we search do so in steps of 4 as HdrS is on a 4-byte aligned
 * address (it is on same alignment as sparc instructions)
 * Return the offset to the HdrS entry (as off_t)
 */
static off_t get_hdrs_offset(int kernelfd, const char *filename)
{
	char buffer[BUFSIZE];
	off_t offset;
	int i;

	if (lseek(kernelfd, 0, SEEK_SET) < 0)
		die("lseek");
	if (read(kernelfd, buffer, BUFSIZE) != BUFSIZE)
		die(filename);

	if (buffer[40] == 'H' && buffer[41] == 'd' &&
	    buffer[42] == 'r' && buffer[43] == 'S') {
		return 40;
	} else {
		/*  Find the gokernel label */
		/* Decode offset from branch instruction */
		offset = ld2(buffer + AOUT_TEXT_OFFSET + 2) << 2;
		/* Go back 512 bytes so we do not miss HdrS */
		offset -= LOOKBACK;
		/* skip a.out header */
		offset += AOUT_TEXT_OFFSET;
		if (offset < 0) {
			errno = -EINVAL;
			die("Calculated a negative offset, probably elftoaout generated an invalid image. Did you use a recent elftoaout ?");
		}
		if (lseek(kernelfd, offset, SEEK_SET) < 0)
			die("lseek");
		if (read(kernelfd, buffer, BUFSIZE) != BUFSIZE)
			die(filename);

		for (i = 0; i < LOOKBACK; i += 4) {
			if (buffer[i + 0] == 'H' && buffer[i + 1] == 'd' &&
			    buffer[i + 2] == 'r' && buffer[i + 3] == 'S') {
				return offset + i;
			}
		}
	}
	fprintf (stderr, "Couldn't find headers signature in %s\n", filename);
	exit(1);
}

int main(int argc,char **argv)
{
	static char aout_magic[] = { 0x01, 0x03, 0x01, 0x07 };
	char buffer[1024];
	unsigned int i, start, end;
	off_t offset;
	struct stat s;
	int image, tail;

	if (argc != 5)
		usage();
	if (strcmp(argv[1], "64") == 0)
		is64bit = 1;
	if (stat (argv[4], &s) < 0)
		die(argv[4]);

	if (!get_start_end(argv[3], &start, &end)) {
		fprintf(stderr, "Could not determine start and end from %s\n",
		        argv[3]);
		exit(1);
	}
	if ((image = open(argv[2], O_RDWR)) < 0)
		die(argv[2]);
	if (read(image, buffer, 512) != 512)
		die(argv[2]);
	if (memcmp(buffer, aout_magic, 4) != 0) {
		fprintf (stderr, "Not a.out. Don't blame me.\n");
		exit(1);
	}
	/*
	 * We need to fill in values for
	 * sparc_ramdisk_image + sparc_ramdisk_size
	 * To locate these symbols search for the "HdrS" text which appear
	 * in the image a little before the gokernel symbol.
	 * See definition of these in init_32.S
	 */

	offset = get_hdrs_offset(image, argv[2]);
	/* skip HdrS + LINUX_VERSION_CODE + HdrS version */
	offset += 10;

	if (lseek(image, offset, 0) < 0)
		die("lseek");

	/*
	 * root_flags = 0
	 * root_dev = 1 (RAMDISK_MAJOR)
	 * ram_flags = 0
	 * sparc_ramdisk_image = "PAGE aligned address after _end")
	 * sparc_ramdisk_size = size of image
	 */
	st4(buffer, 0);
	st4(buffer + 4, 0x01000000);
	st4(buffer + 8, align(end + 32));
	st4(buffer + 12, s.st_size);

	if (write(image, buffer + 2, 14) != 14)
		die(argv[2]);

	/* For sparc64 update a_text and clear a_data + a_bss */
	if (is64bit)
	{
		if (lseek(image, 4, 0) < 0)
			die("lseek");
		/* a_text */
		st4(buffer, align(end + 32 + 8191) - (start & ~0x3fffffUL) +
		            s.st_size);
		/* a_data */
		st4(buffer + 4, 0);
		/* a_bss */
		st4(buffer + 8, 0);
		if (write(image, buffer, 12) != 12)
			die(argv[2]);
	}

	/* seek page aligned boundary in the image file and add boot image */
	if (lseek(image, AOUT_TEXT_OFFSET - start + align(end + 32), 0) < 0)
		die("lseek");
	if ((tail = open(argv[4], O_RDONLY)) < 0)
		die(argv[4]);
	while ((i = read(tail, buffer, 1024)) > 0)
		if (write(image, buffer, i) != i)
			die(argv[2]);
	if (close(image) < 0)
		die("close");
	if (close(tail) < 0)
		die("close");
	return 0;
}