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Java(tm) Binary Kernel Support for Linux v1.03
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----------------------------------------------
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Linux beats them ALL! While all other OS's are TALKING about direct
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support of Java Binaries in the OS, Linux is doing it!
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You can execute Java applications and Java Applets just like any
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other program after you have done the following:
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1) You MUST FIRST install the Java Developers Kit for Linux.
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The Java on Linux HOWTO gives the details on getting and
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installing this. This HOWTO can be found at:
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ftp://sunsite.unc.edu/pub/Linux/docs/HOWTO/Java-HOWTO
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You should also set up a reasonable CLASSPATH environment
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variable to use Java applications that make use of any
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nonstandard classes (not included in the same directory
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as the application itself).
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2) You have to compile BINFMT_MISC either as a module or into
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the kernel (CONFIG_BINFMT_MISC) and set it up properly.
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If you choose to compile it as a module, you will have
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to insert it manually with modprobe/insmod, as kmod
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cannot easily be supported with binfmt_misc.
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Read the file 'binfmt_misc.txt' in this directory to know
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more about the configuration process.
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3) Add the following configuration items to binfmt_misc
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(you should really have read binfmt_misc.txt now):
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support for Java applications:
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':Java:M::\xca\xfe\xba\xbe::/usr/local/bin/javawrapper:'
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support for executable Jar files:
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':ExecutableJAR:E::jar::/usr/local/bin/jarwrapper:'
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support for Java Applets:
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':Applet:E::html::/usr/bin/appletviewer:'
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or the following, if you want to be more selective:
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':Applet:M::<!--applet::/usr/bin/appletviewer:'
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Of cause you have to fix the path names. Given path/file names in this
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document match the Debian 2.1 system. (i.e. jdk installed in /usr,
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custom wrappers from this document in /usr/local)
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Note, that for the more selective applet support you have to modify
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existing html-files to contain <!--applet--> in the first line
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('<' has to be the first character!) to let this work!
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For the compiled Java programs you need a wrapper script like the
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following (this is because Java is broken in case of the filename
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handling), again fix the path names, both in the script and in the
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above given configuration string.
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You, too, need the little program after the script. Compile like
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gcc -O2 -o javaclassname javaclassname.c
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and stick it to /usr/local/bin.
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Both the javawrapper shellscript and the javaclassname program
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were supplied by Colin J. Watson <cjw44@cam.ac.uk>.
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====================== Cut here ===================
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#!/bin/bash
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# /usr/local/bin/javawrapper - the wrapper for binfmt_misc/java
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if [ -z "$1" ]; then
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exec 1>&2
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echo Usage: $0 class-file
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exit 1
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fi
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CLASS=$1
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FQCLASS=`/usr/local/bin/javaclassname $1`
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FQCLASSN=`echo $FQCLASS | sed -e 's/^.*\.\([^.]*\)$/\1/'`
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FQCLASSP=`echo $FQCLASS | sed -e 's-\.-/-g' -e 's-^[^/]*$--' -e 's-/[^/]*$--'`
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# for example:
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# CLASS=Test.class
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# FQCLASS=foo.bar.Test
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# FQCLASSN=Test
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# FQCLASSP=foo/bar
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unset CLASSBASE
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declare -i LINKLEVEL=0
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while :; do
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if [ "`basename $CLASS .class`" == "$FQCLASSN" ]; then
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# See if this directory works straight off
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cd -L `dirname $CLASS`
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CLASSDIR=$PWD
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cd $OLDPWD
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if echo $CLASSDIR | grep -q "$FQCLASSP$"; then
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CLASSBASE=`echo $CLASSDIR | sed -e "s.$FQCLASSP$.."`
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break;
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fi
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# Try dereferencing the directory name
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cd -P `dirname $CLASS`
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CLASSDIR=$PWD
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cd $OLDPWD
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if echo $CLASSDIR | grep -q "$FQCLASSP$"; then
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CLASSBASE=`echo $CLASSDIR | sed -e "s.$FQCLASSP$.."`
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break;
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fi
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# If no other possible filename exists
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if [ ! -L $CLASS ]; then
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exec 1>&2
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echo $0:
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echo " $CLASS should be in a" \
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"directory tree called $FQCLASSP"
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exit 1
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fi
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fi
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if [ ! -L $CLASS ]; then break; fi
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# Go down one more level of symbolic links
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let LINKLEVEL+=1
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if [ $LINKLEVEL -gt 5 ]; then
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exec 1>&2
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echo $0:
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echo " Too many symbolic links encountered"
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exit 1
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fi
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CLASS=`ls --color=no -l $CLASS | sed -e 's/^.* \([^ ]*\)$/\1/'`
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done
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if [ -z "$CLASSBASE" ]; then
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if [ -z "$FQCLASSP" ]; then
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GOODNAME=$FQCLASSN.class
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else
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GOODNAME=$FQCLASSP/$FQCLASSN.class
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fi
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exec 1>&2
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echo $0:
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echo " $FQCLASS should be in a file called $GOODNAME"
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exit 1
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fi
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if ! echo $CLASSPATH | grep -q "^\(.*:\)*$CLASSBASE\(:.*\)*"; then
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# class is not in CLASSPATH, so prepend dir of class to CLASSPATH
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if [ -z "${CLASSPATH}" ] ; then
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export CLASSPATH=$CLASSBASE
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else
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export CLASSPATH=$CLASSBASE:$CLASSPATH
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fi
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fi
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shift
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/usr/bin/java $FQCLASS "$@"
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====================== Cut here ===================
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====================== Cut here ===================
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/* javaclassname.c
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*
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* Extracts the class name from a Java class file; intended for use in a Java
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* wrapper of the type supported by the binfmt_misc option in the Linux kernel.
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*
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* Copyright (C) 1999 Colin J. Watson <cjw44@cam.ac.uk>.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include <stdlib.h>
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#include <stdio.h>
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#include <stdarg.h>
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#include <sys/types.h>
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/* From Sun's Java VM Specification, as tag entries in the constant pool. */
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#define CP_UTF8 1
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#define CP_INTEGER 3
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#define CP_FLOAT 4
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#define CP_LONG 5
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#define CP_DOUBLE 6
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#define CP_CLASS 7
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#define CP_STRING 8
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#define CP_FIELDREF 9
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#define CP_METHODREF 10
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#define CP_INTERFACEMETHODREF 11
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#define CP_NAMEANDTYPE 12
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/* Define some commonly used error messages */
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#define seek_error() error("%s: Cannot seek\n", program)
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#define corrupt_error() error("%s: Class file corrupt\n", program)
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#define eof_error() error("%s: Unexpected end of file\n", program)
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#define utf8_error() error("%s: Only ASCII 1-255 supported\n", program);
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char *program;
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long *pool;
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u_int8_t read_8(FILE *classfile);
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u_int16_t read_16(FILE *classfile);
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void skip_constant(FILE *classfile, u_int16_t *cur);
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void error(const char *format, ...);
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int main(int argc, char **argv);
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/* Reads in an unsigned 8-bit integer. */
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u_int8_t read_8(FILE *classfile)
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{
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int b = fgetc(classfile);
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if(b == EOF)
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eof_error();
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return (u_int8_t)b;
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}
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/* Reads in an unsigned 16-bit integer. */
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u_int16_t read_16(FILE *classfile)
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{
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int b1, b2;
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b1 = fgetc(classfile);
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if(b1 == EOF)
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eof_error();
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b2 = fgetc(classfile);
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if(b2 == EOF)
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eof_error();
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return (u_int16_t)((b1 << 8) | b2);
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}
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/* Reads in a value from the constant pool. */
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void skip_constant(FILE *classfile, u_int16_t *cur)
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{
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u_int16_t len;
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int seekerr = 1;
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pool[*cur] = ftell(classfile);
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switch(read_8(classfile))
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{
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case CP_UTF8:
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len = read_16(classfile);
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seekerr = fseek(classfile, len, SEEK_CUR);
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break;
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case CP_CLASS:
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case CP_STRING:
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seekerr = fseek(classfile, 2, SEEK_CUR);
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break;
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case CP_INTEGER:
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case CP_FLOAT:
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case CP_FIELDREF:
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case CP_METHODREF:
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case CP_INTERFACEMETHODREF:
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case CP_NAMEANDTYPE:
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seekerr = fseek(classfile, 4, SEEK_CUR);
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break;
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case CP_LONG:
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case CP_DOUBLE:
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seekerr = fseek(classfile, 8, SEEK_CUR);
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++(*cur);
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break;
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default:
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corrupt_error();
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}
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if(seekerr)
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seek_error();
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}
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void error(const char *format, ...)
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{
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va_list ap;
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va_start(ap, format);
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vfprintf(stderr, format, ap);
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va_end(ap);
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exit(1);
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}
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int main(int argc, char **argv)
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{
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FILE *classfile;
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u_int16_t cp_count, i, this_class, classinfo_ptr;
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u_int8_t length;
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program = argv[0];
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if(!argv[1])
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error("%s: Missing input file\n", program);
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classfile = fopen(argv[1], "rb");
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if(!classfile)
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error("%s: Error opening %s\n", program, argv[1]);
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if(fseek(classfile, 8, SEEK_SET)) /* skip magic and version numbers */
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seek_error();
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cp_count = read_16(classfile);
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pool = calloc(cp_count, sizeof(long));
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if(!pool)
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error("%s: Out of memory for constant pool\n", program);
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for(i = 1; i < cp_count; ++i)
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skip_constant(classfile, &i);
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if(fseek(classfile, 2, SEEK_CUR)) /* skip access flags */
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seek_error();
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this_class = read_16(classfile);
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if(this_class < 1 || this_class >= cp_count)
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corrupt_error();
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if(!pool[this_class] || pool[this_class] == -1)
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corrupt_error();
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if(fseek(classfile, pool[this_class] + 1, SEEK_SET))
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seek_error();
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classinfo_ptr = read_16(classfile);
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if(classinfo_ptr < 1 || classinfo_ptr >= cp_count)
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corrupt_error();
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if(!pool[classinfo_ptr] || pool[classinfo_ptr] == -1)
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corrupt_error();
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if(fseek(classfile, pool[classinfo_ptr] + 1, SEEK_SET))
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seek_error();
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length = read_16(classfile);
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for(i = 0; i < length; ++i)
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{
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u_int8_t x = read_8(classfile);
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if((x & 0x80) || !x)
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{
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if((x & 0xE0) == 0xC0)
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{
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u_int8_t y = read_8(classfile);
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if((y & 0xC0) == 0x80)
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{
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int c = ((x & 0x1f) << 6) + (y & 0x3f);
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if(c) putchar(c);
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else utf8_error();
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}
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else utf8_error();
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}
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else utf8_error();
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}
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else if(x == '/') putchar('.');
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else putchar(x);
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}
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putchar('\n');
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free(pool);
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fclose(classfile);
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return 0;
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}
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====================== Cut here ===================
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====================== Cut here ===================
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#!/bin/bash
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# /usr/local/java/bin/jarwrapper - the wrapper for binfmt_misc/jar
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java -jar $1
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====================== Cut here ===================
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Now simply chmod +x the .class, .jar and/or .html files you want to execute.
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To add a Java program to your path best put a symbolic link to the main
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.class file into /usr/bin (or another place you like) omitting the .class
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extension. The directory containing the original .class file will be
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added to your CLASSPATH during execution.
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To test your new setup, enter in the following simple Java app, and name
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it "HelloWorld.java":
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class HelloWorld {
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public static void main(String args[]) {
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System.out.println("Hello World!");
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}
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}
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Now compile the application with:
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javac HelloWorld.java
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Set the executable permissions of the binary file, with:
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chmod 755 HelloWorld.class
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And then execute it:
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./HelloWorld.class
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To execute Java Jar files, simple chmod the *.jar files to include
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the execution bit, then just do
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./Application.jar
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To execute Java Applets, simple chmod the *.html files to include
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the execution bit, then just do
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./Applet.html
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originally by Brian A. Lantz, brian@lantz.com
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heavily edited for binfmt_misc by Richard G<EFBFBD>nther
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new scripts by Colin J. Watson <cjw44@cam.ac.uk>
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added executable Jar file support by Kurt Huwig <kurt@iku-netz.de>
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