1               Java(tm) Binary Kernel Support for Linux v1.03
2               ----------------------------------------------
3
4Linux beats them ALL! While all other OS's are TALKING about direct
5support of Java Binaries in the OS, Linux is doing it!
6
7You can execute Java applications and Java Applets just like any
8other program after you have done the following:
9
101) You MUST FIRST install the Java Developers Kit for Linux.
11   The Java on Linux HOWTO gives the details on getting and
12   installing this. This HOWTO can be found at:
13
14	ftp://sunsite.unc.edu/pub/Linux/docs/HOWTO/Java-HOWTO
15
16   You should also set up a reasonable CLASSPATH environment
17   variable to use Java applications that make use of any
18   nonstandard classes (not included in the same directory
19   as the application itself).
20
212) You have to compile BINFMT_MISC either as a module or into
22   the kernel (CONFIG_BINFMT_MISC) and set it up properly.
23   If you choose to compile it as a module, you will have
24   to insert it manually with modprobe/insmod, as kmod
25   cannot easily be supported with binfmt_misc. 
26   Read the file 'binfmt_misc.txt' in this directory to know
27   more about the configuration process.
28
293) Add the following configuration items to binfmt_misc
30   (you should really have read binfmt_misc.txt now):
31   support for Java applications:
32     ':Java:M::\xca\xfe\xba\xbe::/usr/local/bin/javawrapper:'
33   support for executable Jar files:
34     ':ExecutableJAR:E::jar::/usr/local/bin/jarwrapper:'
35   support for Java Applets:
36     ':Applet:E::html::/usr/bin/appletviewer:'
37   or the following, if you want to be more selective:
38     ':Applet:M::<!--applet::/usr/bin/appletviewer:'
39
40   Of course you have to fix the path names. The path/file names given in this
41   document match the Debian 2.1 system. (i.e. jdk installed in /usr,
42   custom wrappers from this document in /usr/local)
43
44   Note, that for the more selective applet support you have to modify
45   existing html-files to contain <!--applet--> in the first line
46   ('<' has to be the first character!) to let this work!
47
48   For the compiled Java programs you need a wrapper script like the
49   following (this is because Java is broken in case of the filename
50   handling), again fix the path names, both in the script and in the
51   above given configuration string.
52
53   You, too, need the little program after the script. Compile like
54   gcc -O2 -o javaclassname javaclassname.c
55   and stick it to /usr/local/bin.
56
57   Both the javawrapper shellscript and the javaclassname program
58   were supplied by Colin J. Watson <cjw44@cam.ac.uk>.
59
60====================== Cut here ===================
61#!/bin/bash
62# /usr/local/bin/javawrapper - the wrapper for binfmt_misc/java
63
64if [ -z "$1" ]; then
65	exec 1>&2
66	echo Usage: $0 class-file
67	exit 1
68fi
69
70CLASS=$1
71FQCLASS=`/usr/local/bin/javaclassname $1`
72FQCLASSN=`echo $FQCLASS | sed -e 's/^.*\.\([^.]*\)$/\1/'`
73FQCLASSP=`echo $FQCLASS | sed -e 's-\.-/-g' -e 's-^[^/]*$--' -e 's-/[^/]*$--'`
74
75# for example:
76# CLASS=Test.class
77# FQCLASS=foo.bar.Test
78# FQCLASSN=Test
79# FQCLASSP=foo/bar
80
81unset CLASSBASE
82
83declare -i LINKLEVEL=0
84
85while :; do
86	if [ "`basename $CLASS .class`" == "$FQCLASSN" ]; then
87		# See if this directory works straight off
88		cd -L `dirname $CLASS`
89		CLASSDIR=$PWD
90		cd $OLDPWD
91		if echo $CLASSDIR | grep -q "$FQCLASSP$"; then
92			CLASSBASE=`echo $CLASSDIR | sed -e "s.$FQCLASSP$.."`
93			break;
94		fi
95		# Try dereferencing the directory name
96		cd -P `dirname $CLASS`
97		CLASSDIR=$PWD
98		cd $OLDPWD
99		if echo $CLASSDIR | grep -q "$FQCLASSP$"; then
100			CLASSBASE=`echo $CLASSDIR | sed -e "s.$FQCLASSP$.."`
101			break;
102		fi
103		# If no other possible filename exists
104		if [ ! -L $CLASS ]; then
105			exec 1>&2
106			echo $0:
107			echo "  $CLASS should be in a" \
108			     "directory tree called $FQCLASSP"
109			exit 1
110		fi
111	fi
112	if [ ! -L $CLASS ]; then break; fi
113	# Go down one more level of symbolic links
114	let LINKLEVEL+=1
115	if [ $LINKLEVEL -gt 5 ]; then
116		exec 1>&2
117		echo $0:
118		echo "  Too many symbolic links encountered"
119		exit 1
120	fi
121	CLASS=`ls --color=no -l $CLASS | sed -e 's/^.* \([^ ]*\)$/\1/'`
122done
123
124if [ -z "$CLASSBASE" ]; then
125	if [ -z "$FQCLASSP" ]; then
126		GOODNAME=$FQCLASSN.class
127	else
128		GOODNAME=$FQCLASSP/$FQCLASSN.class
129	fi
130	exec 1>&2
131	echo $0:
132	echo "  $FQCLASS should be in a file called $GOODNAME"
133	exit 1
134fi
135
136if ! echo $CLASSPATH | grep -q "^\(.*:\)*$CLASSBASE\(:.*\)*"; then
137	# class is not in CLASSPATH, so prepend dir of class to CLASSPATH
138	if [ -z "${CLASSPATH}" ] ; then
139		export CLASSPATH=$CLASSBASE
140	else
141		export CLASSPATH=$CLASSBASE:$CLASSPATH
142	fi
143fi
144
145shift
146/usr/bin/java $FQCLASS "$@"
147====================== Cut here ===================
148
149
150====================== Cut here ===================
151/* javaclassname.c
152 *
153 * Extracts the class name from a Java class file; intended for use in a Java
154 * wrapper of the type supported by the binfmt_misc option in the Linux kernel.
155 *
156 * Copyright (C) 1999 Colin J. Watson <cjw44@cam.ac.uk>.
157 *
158 * This program is free software; you can redistribute it and/or modify
159 * it under the terms of the GNU General Public License as published by
160 * the Free Software Foundation; either version 2 of the License, or
161 * (at your option) any later version.
162 *
163 * This program is distributed in the hope that it will be useful,
164 * but WITHOUT ANY WARRANTY; without even the implied warranty of
165 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
166 * GNU General Public License for more details.
167 *
168 * You should have received a copy of the GNU General Public License
169 * along with this program; if not, write to the Free Software
170 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
171 */
172
173#include <stdlib.h>
174#include <stdio.h>
175#include <stdarg.h>
176#include <sys/types.h>
177
178/* From Sun's Java VM Specification, as tag entries in the constant pool. */
179
180#define CP_UTF8 1
181#define CP_INTEGER 3
182#define CP_FLOAT 4
183#define CP_LONG 5
184#define CP_DOUBLE 6
185#define CP_CLASS 7
186#define CP_STRING 8
187#define CP_FIELDREF 9
188#define CP_METHODREF 10
189#define CP_INTERFACEMETHODREF 11
190#define CP_NAMEANDTYPE 12
191
192/* Define some commonly used error messages */
193
194#define seek_error() error("%s: Cannot seek\n", program)
195#define corrupt_error() error("%s: Class file corrupt\n", program)
196#define eof_error() error("%s: Unexpected end of file\n", program)
197#define utf8_error() error("%s: Only ASCII 1-255 supported\n", program);
198
199char *program;
200
201long *pool;
202
203u_int8_t read_8(FILE *classfile);
204u_int16_t read_16(FILE *classfile);
205void skip_constant(FILE *classfile, u_int16_t *cur);
206void error(const char *format, ...);
207int main(int argc, char **argv);
208
209/* Reads in an unsigned 8-bit integer. */
210u_int8_t read_8(FILE *classfile)
211{
212	int b = fgetc(classfile);
213	if(b == EOF)
214		eof_error();
215	return (u_int8_t)b;
216}
217
218/* Reads in an unsigned 16-bit integer. */
219u_int16_t read_16(FILE *classfile)
220{
221	int b1, b2;
222	b1 = fgetc(classfile);
223	if(b1 == EOF)
224		eof_error();
225	b2 = fgetc(classfile);
226	if(b2 == EOF)
227		eof_error();
228	return (u_int16_t)((b1 << 8) | b2);
229}
230
231/* Reads in a value from the constant pool. */
232void skip_constant(FILE *classfile, u_int16_t *cur)
233{
234	u_int16_t len;
235	int seekerr = 1;
236	pool[*cur] = ftell(classfile);
237	switch(read_8(classfile))
238	{
239	case CP_UTF8:
240		len = read_16(classfile);
241		seekerr = fseek(classfile, len, SEEK_CUR);
242		break;
243	case CP_CLASS:
244	case CP_STRING:
245		seekerr = fseek(classfile, 2, SEEK_CUR);
246		break;
247	case CP_INTEGER:
248	case CP_FLOAT:
249	case CP_FIELDREF:
250	case CP_METHODREF:
251	case CP_INTERFACEMETHODREF:
252	case CP_NAMEANDTYPE:
253		seekerr = fseek(classfile, 4, SEEK_CUR);
254		break;
255	case CP_LONG:
256	case CP_DOUBLE:
257		seekerr = fseek(classfile, 8, SEEK_CUR);
258		++(*cur);
259		break;
260	default:
261		corrupt_error();
262	}
263	if(seekerr)
264		seek_error();
265}
266
267void error(const char *format, ...)
268{
269	va_list ap;
270	va_start(ap, format);
271	vfprintf(stderr, format, ap);
272	va_end(ap);
273	exit(1);
274}
275
276int main(int argc, char **argv)
277{
278	FILE *classfile;
279	u_int16_t cp_count, i, this_class, classinfo_ptr;
280	u_int8_t length;
281
282	program = argv[0];
283
284	if(!argv[1])
285		error("%s: Missing input file\n", program);
286	classfile = fopen(argv[1], "rb");
287	if(!classfile)
288		error("%s: Error opening %s\n", program, argv[1]);
289
290	if(fseek(classfile, 8, SEEK_SET))  /* skip magic and version numbers */
291		seek_error();
292	cp_count = read_16(classfile);
293	pool = calloc(cp_count, sizeof(long));
294	if(!pool)
295		error("%s: Out of memory for constant pool\n", program);
296
297	for(i = 1; i < cp_count; ++i)
298		skip_constant(classfile, &i);
299	if(fseek(classfile, 2, SEEK_CUR))	/* skip access flags */
300		seek_error();
301
302	this_class = read_16(classfile);
303	if(this_class < 1 || this_class >= cp_count)
304		corrupt_error();
305	if(!pool[this_class] || pool[this_class] == -1)
306		corrupt_error();
307	if(fseek(classfile, pool[this_class] + 1, SEEK_SET))
308		seek_error();
309
310	classinfo_ptr = read_16(classfile);
311	if(classinfo_ptr < 1 || classinfo_ptr >= cp_count)
312		corrupt_error();
313	if(!pool[classinfo_ptr] || pool[classinfo_ptr] == -1)
314		corrupt_error();
315	if(fseek(classfile, pool[classinfo_ptr] + 1, SEEK_SET))
316		seek_error();
317
318	length = read_16(classfile);
319	for(i = 0; i < length; ++i)
320	{
321		u_int8_t x = read_8(classfile);
322		if((x & 0x80) || !x)
323		{
324			if((x & 0xE0) == 0xC0)
325			{
326				u_int8_t y = read_8(classfile);
327				if((y & 0xC0) == 0x80)
328				{
329					int c = ((x & 0x1f) << 6) + (y & 0x3f);
330					if(c) putchar(c);
331					else utf8_error();
332				}
333				else utf8_error();
334			}
335			else utf8_error();
336		}
337		else if(x == '/') putchar('.');
338		else putchar(x);
339	}
340	putchar('\n');
341	free(pool);
342	fclose(classfile);
343	return 0;
344}
345====================== Cut here ===================
346
347
348====================== Cut here ===================
349#!/bin/bash
350# /usr/local/java/bin/jarwrapper - the wrapper for binfmt_misc/jar
351
352java -jar $1
353====================== Cut here ===================
354
355
356Now simply chmod +x the .class, .jar and/or .html files you want to execute.
357To add a Java program to your path best put a symbolic link to the main
358.class file into /usr/bin (or another place you like) omitting the .class
359extension. The directory containing the original .class file will be
360added to your CLASSPATH during execution.
361
362
363To test your new setup, enter in the following simple Java app, and name
364it "HelloWorld.java":
365
366	class HelloWorld {
367		public static void main(String args[]) {
368			System.out.println("Hello World!");
369		}
370	}
371
372Now compile the application with:
373	javac HelloWorld.java
374
375Set the executable permissions of the binary file, with:
376	chmod 755 HelloWorld.class
377
378And then execute it:
379	./HelloWorld.class
380
381
382To execute Java Jar files, simple chmod the *.jar files to include
383the execution bit, then just do
384       ./Application.jar
385
386
387To execute Java Applets, simple chmod the *.html files to include
388the execution bit, then just do
389	./Applet.html
390
391
392originally by Brian A. Lantz, brian@lantz.com
393heavily edited for binfmt_misc by Richard Günther
394new scripts by Colin J. Watson <cjw44@cam.ac.uk>
395added executable Jar file support by Kurt Huwig <kurt@iku-netz.de>
396
397