Documentation/admin-guide/java.rst - third_party/kernel - Git at Google


            
            Java(tm) Binary Kernel Support for Linux v1.03

            
            ----------------------------------------------


            Linux beats them ALL! While all other OS's are TALKING about direct

            
            support of Java Binaries in the OS, Linux is doing it!


            You can execute Java applications and Java Applets just like any

            
            other program after you have done the following:


            1) You MUST FIRST install the Java Developers Kit for Linux.

            
               The Java on Linux HOWTO gives the details on getting and

            
               installing this. This HOWTO can be found at:


            	ftp://sunsite.unc.edu/pub/Linux/docs/HOWTO/Java-HOWTO


               You should also set up a reasonable CLASSPATH environment

            
               variable to use Java applications that make use of any

            
               nonstandard classes (not included in the same directory

            
               as the application itself).


            2) You have to compile BINFMT_MISC either as a module or into

            
               the kernel (``CONFIG_BINFMT_MISC``) and set it up properly.

            
               If you choose to compile it as a module, you will have

            
               to insert it manually with modprobe/insmod, as kmod

            
               cannot easily be supported with binfmt_misc.

            
               Read the file 'binfmt_misc.txt' in this directory to know

            
               more about the configuration process.


            3) Add the following configuration items to binfmt_misc

            
               (you should really have read ``binfmt_misc.txt`` now):

            
               support for Java applications::


                 ':Java:M::\xca\xfe\xba\xbe::/usr/local/bin/javawrapper:'


               support for executable Jar files::


                 ':ExecutableJAR:E::jar::/usr/local/bin/jarwrapper:'


               support for Java Applets::


                 ':Applet:E::html::/usr/bin/appletviewer:'


               or the following, if you want to be more selective::


                 ':Applet:M::<!--applet::/usr/bin/appletviewer:'


               Of course you have to fix the path names. The path/file names given in this

            
               document match the Debian 2.1 system. (i.e. jdk installed in ``/usr``,

            
               custom wrappers from this document in ``/usr/local``)


               Note, that for the more selective applet support you have to modify

            
               existing html-files to contain ``<!--applet-->`` in the first line

            
               (``<`` has to be the first character!) to let this work!


               For the compiled Java programs you need a wrapper script like the

            
               following (this is because Java is broken in case of the filename

            
               handling), again fix the path names, both in the script and in the

            
               above given configuration string.


               You, too, need the little program after the script. Compile like::


            	gcc -O2 -o javaclassname javaclassname.c


               and stick it to ``/usr/local/bin``.


               Both the javawrapper shellscript and the javaclassname program

            
               were supplied by Colin J. Watson <cjw44@cam.ac.uk>.


            Javawrapper shell script:


            .. code-block:: sh


              #!/bin/bash

            
              # /usr/local/bin/javawrapper - the wrapper for binfmt_misc/java


              if [ -z "$1" ]; then

            
            	exec 1>&2

            
            	echo Usage: $0 class-file

            
            	exit 1

            
              fi


              CLASS=$1

            
              FQCLASS=`/usr/local/bin/javaclassname $1`

            
              FQCLASSN=`echo $FQCLASS | sed -e 's/^.*\.\([^.]*\)$/\1/'`

            
              FQCLASSP=`echo $FQCLASS | sed -e 's-\.-/-g' -e 's-^[^/]*$--' -e 's-/[^/]*$--'`


              # for example:

            
              # CLASS=Test.class

            
              # FQCLASS=foo.bar.Test

            
              # FQCLASSN=Test

            
              # FQCLASSP=foo/bar


              unset CLASSBASE


              declare -i LINKLEVEL=0


              while :; do

            
            	if [ "`basename $CLASS .class`" == "$FQCLASSN" ]; then

            
            		# See if this directory works straight off

            
            		cd -L `dirname $CLASS`

            
            		CLASSDIR=$PWD

            
            		cd $OLDPWD

            
            		if echo $CLASSDIR | grep -q "$FQCLASSP$"; then

            
            			CLASSBASE=`echo $CLASSDIR | sed -e "s.$FQCLASSP$.."`

            
            			break;

            
            		fi

            
            		# Try dereferencing the directory name

            
            		cd -P `dirname $CLASS`

            
            		CLASSDIR=$PWD

            
            		cd $OLDPWD

            
            		if echo $CLASSDIR | grep -q "$FQCLASSP$"; then

            
            			CLASSBASE=`echo $CLASSDIR | sed -e "s.$FQCLASSP$.."`

            
            			break;

            
            		fi

            
            		# If no other possible filename exists

            
            		if [ ! -L $CLASS ]; then

            
            			exec 1>&2

            
            			echo $0:

            
            			echo "  $CLASS should be in a" \

            
            			     "directory tree called $FQCLASSP"

            
            			exit 1

            
            		fi

            
            	fi

            
            	if [ ! -L $CLASS ]; then break; fi

            
            	# Go down one more level of symbolic links

            
            	let LINKLEVEL+=1

            
            	if [ $LINKLEVEL -gt 5 ]; then

            
            		exec 1>&2

            
            		echo $0:

            
            		echo "  Too many symbolic links encountered"

            
            		exit 1

            
            	fi

            
            	CLASS=`ls --color=no -l $CLASS | sed -e 's/^.* \([^ ]*\)$/\1/'`

            
              done


              if [ -z "$CLASSBASE" ]; then

            
            	if [ -z "$FQCLASSP" ]; then

            
            		GOODNAME=$FQCLASSN.class

            
            	else

            
            		GOODNAME=$FQCLASSP/$FQCLASSN.class

            
            	fi

            
            	exec 1>&2

            
            	echo $0:

            
            	echo "  $FQCLASS should be in a file called $GOODNAME"

            
            	exit 1

            
              fi


              if ! echo $CLASSPATH | grep -q "^\(.*:\)*$CLASSBASE\(:.*\)*"; then

            
            	# class is not in CLASSPATH, so prepend dir of class to CLASSPATH

            
            	if [ -z "${CLASSPATH}" ] ; then

            
            		export CLASSPATH=$CLASSBASE

            
            	else

            
            		export CLASSPATH=$CLASSBASE:$CLASSPATH

            
            	fi

            
              fi


              shift

            
              /usr/bin/java $FQCLASS "$@"


            javaclassname.c:


            .. code-block:: c


              /* javaclassname.c

            
               *

            
               * Extracts the class name from a Java class file; intended for use in a Java

            
               * wrapper of the type supported by the binfmt_misc option in the Linux kernel.

            
               *

            
               * Copyright (C) 1999 Colin J. Watson <cjw44@cam.ac.uk>.

            
               *

            
               * 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

            
               */


              #include <stdlib.h>

            
              #include <stdio.h>

            
              #include <stdarg.h>

            
              #include <sys/types.h>


              /* From Sun's Java VM Specification, as tag entries in the constant pool. */


              #define CP_UTF8 1

            
              #define CP_INTEGER 3

            
              #define CP_FLOAT 4

            
              #define CP_LONG 5

            
              #define CP_DOUBLE 6

            
              #define CP_CLASS 7

            
              #define CP_STRING 8

            
              #define CP_FIELDREF 9

            
              #define CP_METHODREF 10

            
              #define CP_INTERFACEMETHODREF 11

            
              #define CP_NAMEANDTYPE 12

            
              #define CP_METHODHANDLE 15

            
              #define CP_METHODTYPE 16

            
              #define CP_INVOKEDYNAMIC 18


              /* Define some commonly used error messages */


              #define seek_error() error("%s: Cannot seek\n", program)

            
              #define corrupt_error() error("%s: Class file corrupt\n", program)

            
              #define eof_error() error("%s: Unexpected end of file\n", program)

            
              #define utf8_error() error("%s: Only ASCII 1-255 supported\n", program);


              char *program;


              long *pool;


              u_int8_t read_8(FILE *classfile);

            
              u_int16_t read_16(FILE *classfile);

            
              void skip_constant(FILE *classfile, u_int16_t *cur);

            
              void error(const char *format, ...);

            
              int main(int argc, char **argv);


              /* Reads in an unsigned 8-bit integer. */

            
              u_int8_t read_8(FILE *classfile)

            
              {

            
            	int b = fgetc(classfile);

            
            	if(b == EOF)

            
            		eof_error();

            
            	return (u_int8_t)b;

            
              }


              /* Reads in an unsigned 16-bit integer. */

            
              u_int16_t read_16(FILE *classfile)

            
              {

            
            	int b1, b2;

            
            	b1 = fgetc(classfile);

            
            	if(b1 == EOF)

            
            		eof_error();

            
            	b2 = fgetc(classfile);

            
            	if(b2 == EOF)

            
            		eof_error();

            
            	return (u_int16_t)((b1 << 8) | b2);

            
              }


              /* Reads in a value from the constant pool. */

            
              void skip_constant(FILE *classfile, u_int16_t *cur)

            
              {

            
            	u_int16_t len;

            
            	int seekerr = 1;

            
            	pool[*cur] = ftell(classfile);

            
            	switch(read_8(classfile))

            
            	{

            
            	case CP_UTF8:

            
            		len = read_16(classfile);

            
            		seekerr = fseek(classfile, len, SEEK_CUR);

            
            		break;

            
            	case CP_CLASS:

            
            	case CP_STRING:

            
            	case CP_METHODTYPE:

            
            		seekerr = fseek(classfile, 2, SEEK_CUR);

            
            		break;

            
            	case CP_METHODHANDLE:

            
            		seekerr = fseek(classfile, 3, SEEK_CUR);

            
            		break;

            
            	case CP_INTEGER:

            
            	case CP_FLOAT:

            
            	case CP_FIELDREF:

            
            	case CP_METHODREF:

            
            	case CP_INTERFACEMETHODREF:

            
            	case CP_NAMEANDTYPE:

            
            	case CP_INVOKEDYNAMIC:

            
            		seekerr = fseek(classfile, 4, SEEK_CUR);

            
            		break;

            
            	case CP_LONG:

            
            	case CP_DOUBLE:

            
            		seekerr = fseek(classfile, 8, SEEK_CUR);

            
            		++(*cur);

            
            		break;

            
            	default:

            
            		corrupt_error();

            
            	}

            
            	if(seekerr)

            
            		seek_error();

            
              }


              void error(const char *format, ...)

            
              {

            
            	va_list ap;

            
            	va_start(ap, format);

            
            	vfprintf(stderr, format, ap);

            
            	va_end(ap);

            
            	exit(1);

            
              }


              int main(int argc, char **argv)

            
              {

            
            	FILE *classfile;

            
            	u_int16_t cp_count, i, this_class, classinfo_ptr;

            
            	u_int8_t length;


            	program = argv[0];


            	if(!argv[1])

            
            		error("%s: Missing input file\n", program);

            
            	classfile = fopen(argv[1], "rb");

            
            	if(!classfile)

            
            		error("%s: Error opening %s\n", program, argv[1]);


            	if(fseek(classfile, 8, SEEK_SET))  /* skip magic and version numbers */

            
            		seek_error();

            
            	cp_count = read_16(classfile);

            
            	pool = calloc(cp_count, sizeof(long));

            
            	if(!pool)

            
            		error("%s: Out of memory for constant pool\n", program);


            	for(i = 1; i < cp_count; ++i)

            
            		skip_constant(classfile, &i);

            
            	if(fseek(classfile, 2, SEEK_CUR))	/* skip access flags */

            
            		seek_error();


            	this_class = read_16(classfile);

            
            	if(this_class < 1 || this_class >= cp_count)

            
            		corrupt_error();

            
            	if(!pool[this_class] || pool[this_class] == -1)

            
            		corrupt_error();

            
            	if(fseek(classfile, pool[this_class] + 1, SEEK_SET))

            
            		seek_error();


            	classinfo_ptr = read_16(classfile);

            
            	if(classinfo_ptr < 1 || classinfo_ptr >= cp_count)

            
            		corrupt_error();

            
            	if(!pool[classinfo_ptr] || pool[classinfo_ptr] == -1)

            
            		corrupt_error();

            
            	if(fseek(classfile, pool[classinfo_ptr] + 1, SEEK_SET))

            
            		seek_error();


            	length = read_16(classfile);

            
            	for(i = 0; i < length; ++i)

            
            	{

            
            		u_int8_t x = read_8(classfile);

            
            		if((x & 0x80) || !x)

            
            		{

            
            			if((x & 0xE0) == 0xC0)

            
            			{

            
            				u_int8_t y = read_8(classfile);

            
            				if((y & 0xC0) == 0x80)

            
            				{

            
            					int c = ((x & 0x1f) << 6) + (y & 0x3f);

            
            					if(c) putchar(c);

            
            					else utf8_error();

            
            				}

            
            				else utf8_error();

            
            			}

            
            			else utf8_error();

            
            		}

            
            		else if(x == '/') putchar('.');

            
            		else putchar(x);

            
            	}

            
            	putchar('\n');

            
            	free(pool);

            
            	fclose(classfile);

            
            	return 0;

            
              }


            jarwrapper::


              #!/bin/bash

            
              # /usr/local/java/bin/jarwrapper - the wrapper for binfmt_misc/jar


              java -jar $1


            Now simply ``chmod +x`` the ``.class``, ``.jar`` and/or ``.html`` files you

            
            want to execute.


            To add a Java program to your path best put a symbolic link to the main

            
            .class file into /usr/bin (or another place you like) omitting the .class

            
            extension. The directory containing the original .class file will be

            
            added to your CLASSPATH during execution.


            To test your new setup, enter in the following simple Java app, and name

            
            it "HelloWorld.java":


            .. code-block:: java


            	class HelloWorld {

            
            		public static void main(String args[]) {

            
            			System.out.println("Hello World!");

            
            		}

            
            	}


            Now compile the application with::


            	javac HelloWorld.java


            Set the executable permissions of the binary file, with::


            	chmod 755 HelloWorld.class


            And then execute it::


            	./HelloWorld.class


            To execute Java Jar files, simple chmod the ``*.jar`` files to include

            
            the execution bit, then just do::


                   ./Application.jar


            To execute Java Applets, simple chmod the ``*.html`` files to include

            
            the execution bit, then just do::


            	./Applet.html


            originally by Brian A. Lantz, brian@lantz.com

            
            heavily edited for binfmt_misc by Richard Günther

            
            new scripts by Colin J. Watson <cjw44@cam.ac.uk>

            
            added executable Jar file support by Kurt Huwig <kurt@iku-netz.de>
	Java(tm) Binary Kernel Support for Linux v1.03
	----------------------------------------------

	Linux beats them ALL! While all other OS's are TALKING about direct
	support of Java Binaries in the OS, Linux is doing it!

	You can execute Java applications and Java Applets just like any
	other program after you have done the following:

	1) You MUST FIRST install the Java Developers Kit for Linux.
	The Java on Linux HOWTO gives the details on getting and
	installing this. This HOWTO can be found at:

	ftp://sunsite.unc.edu/pub/Linux/docs/HOWTO/Java-HOWTO

	You should also set up a reasonable CLASSPATH environment
	variable to use Java applications that make use of any
	nonstandard classes (not included in the same directory
	as the application itself).

	2) You have to compile BINFMT_MISC either as a module or into
	the kernel (``CONFIG_BINFMT_MISC``) and set it up properly.
	If you choose to compile it as a module, you will have
	to insert it manually with modprobe/insmod, as kmod
	cannot easily be supported with binfmt_misc.
	Read the file 'binfmt_misc.txt' in this directory to know
	more about the configuration process.

	3) Add the following configuration items to binfmt_misc
	(you should really have read ``binfmt_misc.txt`` now):
	support for Java applications::

	':Java:M::\xca\xfe\xba\xbe::/usr/local/bin/javawrapper:'

	support for executable Jar files::

	':ExecutableJAR:E::jar::/usr/local/bin/jarwrapper:'

	support for Java Applets::

	':Applet:E::html::/usr/bin/appletviewer:'

	or the following, if you want to be more selective::

	':Applet:M::<!--applet::/usr/bin/appletviewer:'

	Of course you have to fix the path names. The path/file names given in this
	document match the Debian 2.1 system. (i.e. jdk installed in ``/usr``,
	custom wrappers from this document in ``/usr/local``)

	Note, that for the more selective applet support you have to modify
	existing html-files to contain ``<!--applet-->`` in the first line
	(``<`` has to be the first character!) to let this work!

	For the compiled Java programs you need a wrapper script like the
	following (this is because Java is broken in case of the filename
	handling), again fix the path names, both in the script and in the
	above given configuration string.

	You, too, need the little program after the script. Compile like::

	gcc -O2 -o javaclassname javaclassname.c

	and stick it to ``/usr/local/bin``.

	Both the javawrapper shellscript and the javaclassname program
	were supplied by Colin J. Watson <cjw44@cam.ac.uk>.

	Javawrapper shell script:

	.. code-block:: sh

	#!/bin/bash
	# /usr/local/bin/javawrapper - the wrapper for binfmt_misc/java

	if [ -z "$1" ]; then
	exec 1>&2
	echo Usage: $0 class-file
	exit 1
	fi

	CLASS=$1
	FQCLASS=`/usr/local/bin/javaclassname $1`
	FQCLASSN=`echo $FQCLASS \| sed -e 's/^.\.\([^.]\)$/\1/'`
	FQCLASSP=`echo $FQCLASS \| sed -e 's-\.-/-g' -e 's-^[^/]$--' -e 's-/[^/]$--'`

	# for example:
	# CLASS=Test.class
	# FQCLASS=foo.bar.Test
	# FQCLASSN=Test
	# FQCLASSP=foo/bar

	unset CLASSBASE

	declare -i LINKLEVEL=0

	while :; do
	if [ "`basename $CLASS .class`" == "$FQCLASSN" ]; then
	# See if this directory works straight off
	cd -L `dirname $CLASS`
	CLASSDIR=$PWD
	cd $OLDPWD
	if echo $CLASSDIR \| grep -q "$FQCLASSP$"; then
	CLASSBASE=`echo $CLASSDIR \| sed -e "s.$FQCLASSP$.."`
	break;
	fi
	# Try dereferencing the directory name
	cd -P `dirname $CLASS`
	CLASSDIR=$PWD
	cd $OLDPWD
	if echo $CLASSDIR \| grep -q "$FQCLASSP$"; then
	CLASSBASE=`echo $CLASSDIR \| sed -e "s.$FQCLASSP$.."`
	break;
	fi
	# If no other possible filename exists
	if [ ! -L $CLASS ]; then
	exec 1>&2
	echo $0:
	echo " $CLASS should be in a" \
	"directory tree called $FQCLASSP"
	exit 1
	fi
	fi
	if [ ! -L $CLASS ]; then break; fi
	# Go down one more level of symbolic links
	let LINKLEVEL+=1
	if [ $LINKLEVEL -gt 5 ]; then
	exec 1>&2
	echo $0:
	echo " Too many symbolic links encountered"
	exit 1
	fi
	CLASS=`ls --color=no -l $CLASS \| sed -e 's/^.* \([^ ]*\)$/\1/'`
	done

	if [ -z "$CLASSBASE" ]; then
	if [ -z "$FQCLASSP" ]; then
	GOODNAME=$FQCLASSN.class
	else
	GOODNAME=$FQCLASSP/$FQCLASSN.class
	fi
	exec 1>&2
	echo $0:
	echo " $FQCLASS should be in a file called $GOODNAME"
	exit 1
	fi

	if ! echo $CLASSPATH \| grep -q "^\(.:\)$CLASSBASE\(:.\)"; then
	# class is not in CLASSPATH, so prepend dir of class to CLASSPATH
	if [ -z "${CLASSPATH}" ] ; then
	export CLASSPATH=$CLASSBASE
	else
	export CLASSPATH=$CLASSBASE:$CLASSPATH
	fi
	fi

	shift
	/usr/bin/java $FQCLASS "$@"

	javaclassname.c:

	.. code-block:: c

	/* javaclassname.c
	*
	* Extracts the class name from a Java class file; intended for use in a Java
	* wrapper of the type supported by the binfmt_misc option in the Linux kernel.
	*
	* Copyright (C) 1999 Colin J. Watson <cjw44@cam.ac.uk>.
	*
	* 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
	*/

	#include <stdlib.h>
	#include <stdio.h>
	#include <stdarg.h>
	#include <sys/types.h>

	/* From Sun's Java VM Specification, as tag entries in the constant pool. */

	#define CP_UTF8 1
	#define CP_INTEGER 3
	#define CP_FLOAT 4
	#define CP_LONG 5
	#define CP_DOUBLE 6
	#define CP_CLASS 7
	#define CP_STRING 8
	#define CP_FIELDREF 9
	#define CP_METHODREF 10
	#define CP_INTERFACEMETHODREF 11
	#define CP_NAMEANDTYPE 12
	#define CP_METHODHANDLE 15
	#define CP_METHODTYPE 16
	#define CP_INVOKEDYNAMIC 18

	/* Define some commonly used error messages */

	#define seek_error() error("%s: Cannot seek\n", program)
	#define corrupt_error() error("%s: Class file corrupt\n", program)
	#define eof_error() error("%s: Unexpected end of file\n", program)
	#define utf8_error() error("%s: Only ASCII 1-255 supported\n", program);

	char *program;

	long *pool;

	u_int8_t read_8(FILE *classfile);
	u_int16_t read_16(FILE *classfile);
	void skip_constant(FILE classfile, u_int16_t cur);
	void error(const char *format, ...);
	int main(int argc, char **argv);

	/* Reads in an unsigned 8-bit integer. */
	u_int8_t read_8(FILE *classfile)
	{
	int b = fgetc(classfile);
	if(b == EOF)
	eof_error();
	return (u_int8_t)b;
	}

	/* Reads in an unsigned 16-bit integer. */
	u_int16_t read_16(FILE *classfile)
	{
	int b1, b2;
	b1 = fgetc(classfile);
	if(b1 == EOF)
	eof_error();
	b2 = fgetc(classfile);
	if(b2 == EOF)
	eof_error();
	return (u_int16_t)((b1 << 8) \| b2);
	}

	/* Reads in a value from the constant pool. */
	void skip_constant(FILE classfile, u_int16_t cur)
	{
	u_int16_t len;
	int seekerr = 1;
	pool[*cur] = ftell(classfile);
	switch(read_8(classfile))
	{
	case CP_UTF8:
	len = read_16(classfile);
	seekerr = fseek(classfile, len, SEEK_CUR);
	break;
	case CP_CLASS:
	case CP_STRING:
	case CP_METHODTYPE:
	seekerr = fseek(classfile, 2, SEEK_CUR);
	break;
	case CP_METHODHANDLE:
	seekerr = fseek(classfile, 3, SEEK_CUR);
	break;
	case CP_INTEGER:
	case CP_FLOAT:
	case CP_FIELDREF:
	case CP_METHODREF:
	case CP_INTERFACEMETHODREF:
	case CP_NAMEANDTYPE:
	case CP_INVOKEDYNAMIC:
	seekerr = fseek(classfile, 4, SEEK_CUR);
	break;
	case CP_LONG:
	case CP_DOUBLE:
	seekerr = fseek(classfile, 8, SEEK_CUR);
	++(*cur);
	break;
	default:
	corrupt_error();
	}
	if(seekerr)
	seek_error();
	}

	void error(const char *format, ...)
	{
	va_list ap;
	va_start(ap, format);
	vfprintf(stderr, format, ap);
	va_end(ap);
	exit(1);
	}

	int main(int argc, char **argv)
	{
	FILE *classfile;
	u_int16_t cp_count, i, this_class, classinfo_ptr;
	u_int8_t length;

	program = argv[0];

	if(!argv[1])
	error("%s: Missing input file\n", program);
	classfile = fopen(argv[1], "rb");
	if(!classfile)
	error("%s: Error opening %s\n", program, argv[1]);

	if(fseek(classfile, 8, SEEK_SET)) /* skip magic and version numbers */
	seek_error();
	cp_count = read_16(classfile);
	pool = calloc(cp_count, sizeof(long));
	if(!pool)
	error("%s: Out of memory for constant pool\n", program);

	for(i = 1; i < cp_count; ++i)
	skip_constant(classfile, &i);
	if(fseek(classfile, 2, SEEK_CUR)) /* skip access flags */
	seek_error();

	this_class = read_16(classfile);
	if(this_class < 1 \|\| this_class >= cp_count)
	corrupt_error();
	if(!pool[this_class] \|\| pool[this_class] == -1)
	corrupt_error();
	if(fseek(classfile, pool[this_class] + 1, SEEK_SET))
	seek_error();

	classinfo_ptr = read_16(classfile);
	if(classinfo_ptr < 1 \|\| classinfo_ptr >= cp_count)
	corrupt_error();
	if(!pool[classinfo_ptr] \|\| pool[classinfo_ptr] == -1)
	corrupt_error();
	if(fseek(classfile, pool[classinfo_ptr] + 1, SEEK_SET))
	seek_error();

	length = read_16(classfile);
	for(i = 0; i < length; ++i)
	{
	u_int8_t x = read_8(classfile);
	if((x & 0x80) \|\| !x)
	{
	if((x & 0xE0) == 0xC0)
	{
	u_int8_t y = read_8(classfile);
	if((y & 0xC0) == 0x80)
	{
	int c = ((x & 0x1f) << 6) + (y & 0x3f);
	if(c) putchar(c);
	else utf8_error();
	}
	else utf8_error();
	}
	else utf8_error();
	}
	else if(x == '/') putchar('.');
	else putchar(x);
	}
	putchar('\n');
	free(pool);
	fclose(classfile);
	return 0;
	}

	jarwrapper::

	#!/bin/bash
	# /usr/local/java/bin/jarwrapper - the wrapper for binfmt_misc/jar

	java -jar $1


	Now simply ``chmod +x`` the ``.class``, ``.jar`` and/or ``.html`` files you
	want to execute.

	To add a Java program to your path best put a symbolic link to the main
	.class file into /usr/bin (or another place you like) omitting the .class
	extension. The directory containing the original .class file will be
	added to your CLASSPATH during execution.


	To test your new setup, enter in the following simple Java app, and name
	it "HelloWorld.java":

	.. code-block:: java

	class HelloWorld {
	public static void main(String args[]) {
	System.out.println("Hello World!");
	}
	}

	Now compile the application with::

	javac HelloWorld.java

	Set the executable permissions of the binary file, with::

	chmod 755 HelloWorld.class

	And then execute it::

	./HelloWorld.class


	To execute Java Jar files, simple chmod the ``*.jar`` files to include
	the execution bit, then just do::

	./Application.jar


	To execute Java Applets, simple chmod the ``*.html`` files to include
	the execution bit, then just do::

	./Applet.html


	originally by Brian A. Lantz, brian@lantz.com
	heavily edited for binfmt_misc by Richard Günther
	new scripts by Colin J. Watson <cjw44@cam.ac.uk>
	added executable Jar file support by Kurt Huwig <kurt@iku-netz.de>