tool for editing builtin command line

[Amos Waterland]

The following is a tool for reading and editing the builtin command line
arguments in Linux zImage files and other bootable files that follow the
same format.  It is useful in a cluster context in which one is booting
the same kernel on many machines with the only difference being their
network autoconfiguration values.  Inspired by a script that Michal
Ostrowski posted earlier.

To see the existing arguments in a bootable image:

 $ ./builtin-cmdline zImage
 console=ttyS0,19200

To put new arguments in the image:

 $ ./builtin-cmdline zImage "ro root=/dev/nfs nfsroot=192.168.0.3:/nfsroot \
                 ip=192.168.0.4::192.168.0.2:255.255.255.0:cluster001:eth0:off"

Signed-off-by: Amos Waterland <apw at us.ibm.com>

---

#!/bin/bash
#
# Copyright (C) 2006 Amos Waterland <apw at us.ibm.com>, IBM Corp.
#
# 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA

function help()
{
    local name=$1;
    local version=$2;

    echo -e "\`$name' manipulates builtin command line arguments\n" \
	    "\n" \
	    "Usage: $name FILE [ARGS]\n" \
	    " -?, --help     Show this help statement.\n" \
	    "     --version  Show version statement.\n" \
	    "\n" \
	    "Examples: $name zImage\n" \
            "          $name zImage 'console=ttyS0'";
}

function work()
{
    local file=$1;
    local args=$2;
    local off; local siz; local out;

    off=$(objdump -h $file |
       	  gawk -- '{if($2=="__builtin_cmdline") {print strtonum("0x"$6);}}';)

    if [ -z $off ]; then
        echo "error: cannot find command line section in: $file"; return 1;
    fi

    siz=$(objdump -h $file |
       	  gawk -- '{if($2=="__builtin_cmdline") {print strtonum("0x"$3);}}';)

    if [ -z $siz ]; then return 1; fi

    if [ -z "$args" ]; then
        out=$(dd bs=1 if=$file skip=$off count=$siz 2>/dev/null);
        if [ $? -ne 0 ]; then return 1; fi
        echo $out;
    else
        dd if=/dev/zero of=$file bs=1 \
           seek=$off conv=notrunc count=$siz 2>/dev/null
        if [ $? -ne 0 ]; then return 1; fi
        echo -n "$args" | dd \
           of=$file bs=1 seek=$off conv=notrunc count=$siz 2>/dev/null
        if [ $? -ne 0 ]; then return 1; fi
    fi

    return 0;
}

function main()
{
    local args;
    local file;
    local name=builtin-cmdline;
    local version=0.1.0;

    while [ $# -gt 0 ]; do
        case $1 in
        -\? | --help)
            help $name $version; return 1;
            ;;
        --version)
            echo "$name $version"; return 1;
            ;;
        *)
	    if [ -z "$file" ]; then
	        file="$1"; shift;
	    elif [ -z "$args" ]; then
	        args="$1"; shift;
	    else
                help $name $version; return 1;
	    fi
            ;;
        esac
    done

    [ -z "$file" ] && {
	help $name $version; return 1;
    }

    work "$file" "$args" || {
	echo "bailing out because of errors"; return 1;
    }

    return 0;
}

main "$@";
exit $?;