piggyback.c

Go to the documentation of this file.

/*
   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]>

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */

#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 (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;
}