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 #define CP_METHODHANDLE 15
 192 #define CP_METHODTYPE 16
 193 #define CP_INVOKEDYNAMIC 18
 194
 195 /* Define some commonly used error messages */
 196
 197 #define seek_error() error("%s: Cannot seek\n", program)
 198 #define corrupt_error() error("%s: Class file corrupt\n", program)
 199 #define eof_error() error("%s: Unexpected end of file\n", program)
 200 #define utf8_error() error("%s: Only ASCII 1-255 supported\n", program);
 201
 202 char *program;
 203
 204 long *pool;
 205
 206 u_int8_t read_8(FILE *classfile);
 207 u_int16_t read_16(FILE *classfile);
 208 void skip_constant(FILE *classfile, u_int16_t *cur);
 209 void error(const char *format, ...);
 210 int main(int argc, char **argv);
 211
 212 /* Reads in an unsigned 8-bit integer. */
 213 u_int8_t read_8(FILE *classfile)
 214 {
 215         int b = fgetc(classfile);
 216         if(b == EOF)
 217                 eof_error();
 218         return (u_int8_t)b;
 219 }
 220
 221 /* Reads in an unsigned 16-bit integer. */
 222 u_int16_t read_16(FILE *classfile)
 223 {
 224         int b1, b2;
 225         b1 = fgetc(classfile);
 226         if(b1 == EOF)
 227                 eof_error();
 228         b2 = fgetc(classfile);
 229         if(b2 == EOF)
 230                 eof_error();
 231         return (u_int16_t)((b1 << 8) | b2);
 232 }
 233
 234 /* Reads in a value from the constant pool. */
 235 void skip_constant(FILE *classfile, u_int16_t *cur)
 236 {
 237         u_int16_t len;
 238         int seekerr = 1;
 239         pool[*cur] = ftell(classfile);
 240         switch(read_8(classfile))
 241         {
 242         case CP_UTF8:
 243                 len = read_16(classfile);
 244                 seekerr = fseek(classfile, len, SEEK_CUR);
 245                 break;
 246         case CP_CLASS:
 247         case CP_STRING:
 248         case CP_METHODTYPE:
 249                 seekerr = fseek(classfile, 2, SEEK_CUR);
 250                 break;
 251         case CP_METHODHANDLE:
 252                 seekerr = fseek(classfile, 3, SEEK_CUR);
 253                 break;
 254         case CP_INTEGER:
 255         case CP_FLOAT:
 256         case CP_FIELDREF:
 257         case CP_METHODREF:
 258         case CP_INTERFACEMETHODREF:
 259         case CP_NAMEANDTYPE:
 260         case CP_INVOKEDYNAMIC:
 261                 seekerr = fseek(classfile, 4, SEEK_CUR);
 262                 break;
 263         case CP_LONG:
 264         case CP_DOUBLE:
 265                 seekerr = fseek(classfile, 8, SEEK_CUR);
 266                 ++(*cur);
 267                 break;
 268         default:
 269                 corrupt_error();
 270         }
 271         if(seekerr)
 272                 seek_error();
 273 }
 274
 275 void error(const char *format, ...)
 276 {
 277         va_list ap;
 278         va_start(ap, format);
 279         vfprintf(stderr, format, ap);
 280         va_end(ap);
 281         exit(1);
 282 }
 283
 284 int main(int argc, char **argv)
 285 {
 286         FILE *classfile;
 287         u_int16_t cp_count, i, this_class, classinfo_ptr;
 288         u_int8_t length;
 289
 290         program = argv[0];
 291
 292         if(!argv[1])
 293                 error("%s: Missing input file\n", program);
 294         classfile = fopen(argv[1], "rb");
 295         if(!classfile)
 296                 error("%s: Error opening %s\n", program, argv[1]);
 297
 298         if(fseek(classfile, 8, SEEK_SET))  /* skip magic and version numbers */
 299                 seek_error();
 300         cp_count = read_16(classfile);
 301         pool = calloc(cp_count, sizeof(long));
 302         if(!pool)
 303                 error("%s: Out of memory for constant pool\n", program);
 304
 305         for(i = 1; i < cp_count; ++i)
 306                 skip_constant(classfile, &i);
 307         if(fseek(classfile, 2, SEEK_CUR))       /* skip access flags */
 308                 seek_error();
 309
 310         this_class = read_16(classfile);
 311         if(this_class < 1 || this_class >= cp_count)
 312                 corrupt_error();
 313         if(!pool[this_class] || pool[this_class] == -1)
 314                 corrupt_error();
 315         if(fseek(classfile, pool[this_class] + 1, SEEK_SET))
 316                 seek_error();
 317
 318         classinfo_ptr = read_16(classfile);
 319         if(classinfo_ptr < 1 || classinfo_ptr >= cp_count)
 320                 corrupt_error();
 321         if(!pool[classinfo_ptr] || pool[classinfo_ptr] == -1)
 322                 corrupt_error();
 323         if(fseek(classfile, pool[classinfo_ptr] + 1, SEEK_SET))
 324                 seek_error();
 325
 326         length = read_16(classfile);
 327         for(i = 0; i < length; ++i)
 328         {
 329                 u_int8_t x = read_8(classfile);
 330                 if((x & 0x80) || !x)
 331                 {
 332                         if((x & 0xE0) == 0xC0)
 333                         {
 334                                 u_int8_t y = read_8(classfile);
 335                                 if((y & 0xC0) == 0x80)
 336                                 {
 337                                         int c = ((x & 0x1f) << 6) + (y & 0x3f);
 338                                         if(c) putchar(c);
 339                                         else utf8_error();
 340                                 }
 341                                 else utf8_error();
 342                         }
 343                         else utf8_error();
 344                 }
 345                 else if(x == '/') putchar('.');
 346                 else putchar(x);
 347         }
 348         putchar('\n');
 349         free(pool);
 350         fclose(classfile);
 351         return 0;
 352 }
 353 ====================== Cut here ===================
 354
 355
 356 ====================== Cut here ===================
 357 #!/bin/bash
 358 # /usr/local/java/bin/jarwrapper - the wrapper for binfmt_misc/jar
 359
 360 java -jar $1
 361 ====================== Cut here ===================
 362
 363
 364 Now simply chmod +x the .class, .jar and/or .html files you want to execute.
 365 To add a Java program to your path best put a symbolic link to the main
 366 .class file into /usr/bin (or another place you like) omitting the .class
 367 extension. The directory containing the original .class file will be
 368 added to your CLASSPATH during execution.
 369
 370
 371 To test your new setup, enter in the following simple Java app, and name
 372 it "HelloWorld.java":
 373
 374         class HelloWorld {
 375                 public static void main(String args[]) {
 376                         System.out.println("Hello World!");
 377                 }
 378         }
 379
 380 Now compile the application with:
 381         javac HelloWorld.java
 382
 383 Set the executable permissions of the binary file, with:
 384         chmod 755 HelloWorld.class
 385
 386 And then execute it:
 387         ./HelloWorld.class
 388
 389
 390 To execute Java Jar files, simple chmod the *.jar files to include
 391 the execution bit, then just do
 392        ./Application.jar
 393
 394
 395 To execute Java Applets, simple chmod the *.html files to include
 396 the execution bit, then just do
 397         ./Applet.html
 398
 399
 400 originally by Brian A. Lantz, brian@lantz.com
 401 heavily edited for binfmt_misc by Richard Günther
 402 new scripts by Colin J. Watson <cjw44@cam.ac.uk>
 403 added executable Jar file support by Kurt Huwig <kurt@iku-netz.de>
 404