Documentation/java.txt

   1                Java(tm) Binary Kernel Support for Linux v1.03
   2                ----------------------------------------------
   3
   4 Linux beats them ALL! While all other OS's are TALKING about direct
   5 support of Java Binaries in the OS, Linux is doing it!
   6
   7 You can execute Java applications and Java Applets just like any
   8 other program after you have done the following:
   9
  10 1) 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
  21 2) 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
  29 3) 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
  64 if [ -z "$1" ]; then
  65         exec 1>&2
  66         echo Usage: $0 class-file
  67         exit 1
  68 fi
  69
  70 CLASS=$1
  71 FQCLASS=`/usr/local/bin/javaclassname $1`
  72 FQCLASSN=`echo $FQCLASS | sed -e 's/^.*\.\([^.]*\)$/\1/'`
  73 FQCLASSP=`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
  81 unset CLASSBASE
  82
  83 declare -i LINKLEVEL=0
  84
  85 while :; 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/^.* \([^ ]*\)$/\1/'`
 122 done
 123
 124 if [ -z "$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
 134 fi
 135
 136 if ! 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
 143 fi
 144
 145 shift
 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
 199 char *program;
 200
 201 long *pool;
 202
 203 u_int8_t read_8(FILE *classfile);
 204 u_int16_t read_16(FILE *classfile);
 205 void skip_constant(FILE *classfile, u_int16_t *cur);
 206 void error(const char *format, ...);
 207 int main(int argc, char **argv);
 208
 209 /* Reads in an unsigned 8-bit integer. */
 210 u_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. */
 219 u_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. */
 232 void 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
 267 void 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
 276 int 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
 352 java -jar $1
 353 ====================== Cut here ===================
 354
 355
 356 Now simply chmod +x the .class, .jar and/or .html files you want to execute.
 357 To 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
 359 extension. The directory containing the original .class file will be
 360 added to your CLASSPATH during execution.
 361
 362
 363 To test your new setup, enter in the following simple Java app, and name
 364 it "HelloWorld.java":
 365
 366         class HelloWorld {
 367                 public static void main(String args[]) {
 368                         System.out.println("Hello World!");
 369                 }
 370         }
 371
 372 Now compile the application with:
 373         javac HelloWorld.java
 374
 375 Set the executable permissions of the binary file, with:
 376         chmod 755 HelloWorld.class
 377
 378 And then execute it:
 379         ./HelloWorld.class
 380
 381
 382 To execute Java Jar files, simple chmod the *.jar files to include
 383 the execution bit, then just do
 384        ./Application.jar
 385
 386
 387 To execute Java Applets, simple chmod the *.html files to include
 388 the execution bit, then just do
 389         ./Applet.html
 390
 391
 392 originally by Brian A. Lantz, brian@lantz.com
 393 heavily edited for binfmt_misc by Richard Günther
 394 new scripts by Colin J. Watson <cjw44@cam.ac.uk>
 395 added executable Jar file support by Kurt Huwig <kurt@iku-netz.de>
 396