The Linux Development Platform Configuring, Using, and ... - Classes

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CH03.fm Page 68 Monday, October 7, 2002 8:33 PM 68 Chapter 3 • Compilers and Assemblers 3.3.7.3 Compiling Java Code Information about the GCC Java compiler gcj is available at http://gcc.gnu.org/java/. Before you can build Java programs, you also need to have libgcj installed. With old compilers, you had to install it separately from source code. When you build and install new versions of GCC, libgcj is installed automatically. If you are still using an old compiler and want to have libgcj installed, information is available at http://gcc.gnu.org/java/libgcj2.html. Briefly the process is as follows: Download libgcj from ftp://sourceware.cygnus.com/pub/java/ or another web site on the Internet. Untar it in /opt directory and a new directory will be created under /opt which will contain source code for libgcj. Create a directory /opt/libgcj-build and move into this directory. After that you have to perform the following sequence of commands: • ../libgcj/configure •make • make install Note that your new compiler must be in PATH before you build libgcj. Now let us see how to compile a Java program. Consider the following simple Java program that prints the message “Hello World”. The source code filename is hello.java. class HelloWorld { public static void main (String args[]) { System.out.print("Hello World "); } } Traditionally you have to invoke the javac program to build a byte code. After that you have to run the byte code using the java program on Linux. However if you use gcj, you can create a binary output file hello using the following command: gcj –main=HelloWorld –o hello hello.java The output file is hello, which is an executable binary. The –main switch is used for the entry point when the program is executed. The compiler uses some information to build Java code. This information includes reading the gcj specification file and libraries. The following command displays this information. [rr@conformix 4]$ gcj -v Reading specs from /opt/gcc-3.0.4/lib/gcc-lib/i686-pc-linuxgnu/3.0.4/specs Reading specs from /opt/gcc-3.0.4/lib/gcc-lib/i686-pc-linuxgnu/3.0.4/../../../libgcj.spec rename spec lib to liborig rename spec startfile to startfileorig
CH03.fm Page 69 Monday, October 7, 2002 8:33 PM Compiling a Program 69 Configured with: ../gcc-3.0.4/configure --prefix=/opt/gcc- 3.0.4 --enable-threads=posix Thread model: posix gcc version 3.0.4 [rr@conformix 4]$ The compilation of Java programs is completed in many steps. Let us compile the hello.java program to build a statically linked hello output binary using the following command. The –v switch shows all of the steps during this process. [rr@conformix 4]$ gcj hello.java --main=HelloWorld -o hello - static -v Reading specs from /opt/gcc-3.0.4/lib/gcc-lib/i686-pc-linuxgnu/3.0.4/specs Reading specs from /opt/gcc-3.0.4/lib/gcc-lib/i686-pc-linuxgnu/3.0.4/../../../libgcj.spec rename spec lib to liborig rename spec startfile to startfileorig Configured with: ../gcc-3.0.4/configure --prefix=/opt/gcc- 3.0.4 --enable-threads=posix Thread model: posix gcc version 3.0.4 /opt/gcc-3.0.4/lib/gcc-lib/i686-pc-linux-gnu/3.0.4/jc1 hello.java -fuse-divide-subroutine -fuse-boehm-gc -fnon-callexceptions -quiet -dumpbase hello.java -g1 -version -o /tmp/ ccHj5WMY.s GNU Java version 3.0.4 (i686-pc-linux-gnu) compiled by GNU C version 3.0.4. as --traditional-format -V -Qy -o /tmp/cchm92Nc.o /tmp/ ccHj5WMY.s GNU assembler version 2.10.91 (i386-redhat-linux) using BFD version 2.10.91.0.2 /opt/gcc-3.0.4/lib/gcc-lib/i686-pc-linux-gnu/3.0.4/jvgenmain HelloWorldmain /tmp/ccTlFcXz.i /opt/gcc-3.0.4/lib/gcc-lib/i686-pc-linux-gnu/3.0.4/cc1 /tmp/ ccTlFcXz.i -quiet -dumpbase HelloWorldmain.c -g1 -version - fdollars-in-identifiers -o /tmp/ccHj5WMY.s GNU CPP version 3.0.4 (cpplib) (i386 Linux/ELF) GNU C version 3.0.4 (i686-pc-linux-gnu) compiled by GNU C version 3.0.4. as --traditional-format -V -Qy -o /tmp/ccBgJjpa.o /tmp/ ccHj5WMY.s GNU assembler version 2.10.91 (i386-redhat-linux) using BFD version 2.10.91.0.2 /opt/gcc-3.0.4/lib/gcc-lib/i686-pc-linux-gnu/3.0.4/collect2 - m elf_i386 -static -o hello /usr/lib/crt1.o /usr/lib/crti.o / opt/gcc-3.0.4/lib/gcc-lib/i686-pc-linux-gnu/3.0.4/crtbegin.o - L/opt/gcc-3.0.4/lib/gcc-lib/i686-pc-linux-gnu/3.0.4 -L/opt/
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