Linux の Java(tm) バイナリのカーネルサポート v1.03

翻訳ソース: http://linuxjf.osdn.jp/JFdocs/kernel-docs-2.6/java.txt.html

Linux はすべてにおいて先んじています！他のすべての OS が、OS 内で Java バイナリの直接サポートについて議論をしている中、Linux はサポートをしています！

下記のことを行った後、他のプログラムと同じように Java アプリケーションと Java アプレットを実行できます:

1. まず、Linux 向け Java Developers Kit (JDK) をインストールしなければなりません。Java-HOWTO は JDK の入手とインストールを説明しています。この HOWTO は次のところから入手できます (訳注：2001 年 12 月現在ではリンク切れになっていました。):

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

   また、標準ではないクラス (アプリケーション自体と同じディレクトリに含まれていないクラスのために) を利用している Java アプリケーションを使用するために、合理的な CLASSPATH 環境変数を設定しなければなりません。

2. モジュールとして、あるいはカーネルに組込む (CONFIG_BINFMT_MISC) ために、BINFMT_MISC をコンパイルし、適切に設定しなければなりません。モジュールとしてコンパイルすることを選んだなら、kmod で binfmt_misc をサポートすることが簡単にできないので、modprobe/insmod により手動でロードしなければなりません。設定についてもっと知りたいのなら、Documentation ディレクトリにあるファイル 'binfmt_misc.txt' を読んでください。

3. binfmt_misc に次の設定項目を追加してください (いますぐ binfmt_misc.txt を読むことをお勧めします): Java アプリケーションのサポート:

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

   実行可能 jar ファイルのサポート:

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

   Java アプレットのサポート:

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

   もしくは、より選択的にしたい場合:

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

   もちろんパス名を修正しなければなりません。この文書で使用しているパスやファイル名は Debian 2.1 システムに合わせています (つまり は /usr 内に、この文書のカスタムラッパーは /usr/local 内にインストールされています)。

   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:

#!/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:

/* 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":

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>