Soot overview/Disassembling classfiles

Raja Vallée-Rai (

March 15, 2000


By the end of this lesson, the student should be able to:

Testing your Installation

This is an interactive tutorial. So the first thing you must do is test your installation. This can be done by typing java soot.Main at the shell prompt. If your installation is incorrect you should get a class "soot.Main" not found exception. Please refer to the installation instructions which came with the Soot software if this occurs. If your installation is correct you should see something like:

~ $ java soot.Main
Soot version 2.0
Copyright (C) 1997-2003 Raja Vallee-Rai and others.
All rights reserved.

Contributions are copyright (C) 1997-2003 by their respective contributors.
See the file 'credits' for a list of contributors.
See individual source files for details.

Soot comes with ABSOLUTELY NO WARRANTY.  Soot is free software,
and you are welcome to redistribute it under certain conditions.
See the accompanying file 'COPYING-LESSER.txt' for details.

Visit the Soot website:

For a list of command line options, enter:
  java soot.Main --help

What is Soot?

Soot has two fundamental uses; it can be used as a stand-alone command line tool or as a Java compiler framework. As a command line tool, Soot can:

  1. dissassemble classfiles
  2. assemble classfiles
  3. optimize classfiles

As a Java compiler framework, Soot can be used as a testbed for developing new optimizations. These new optimizations can then be added to the base set of optimizations invoked by the command line Soot tool. The optimizations that can be added can either be applied to single classfiles or entire applications.

Soot accomplishes these myriad tasks by being able to process classfiles in a variety of different forms. Currently Soot inputs two different intermediate representations (classfiles or Jimple code), and outputs any of its intermediate representations. By invoking Soot with the -help option, you can see the output formats:

> java soot.Main --help
Output Options:
  -d DIR -output-dir DIR       Store output files in DIR 
  -f FORMAT -output-format FORMAT
                               Set output format for Soot 
     J jimple                    Produce .jimple Files 
     j jimp                      Produce .jimp (abbreviated Jimple) files 
     S shimple                   Produce .shimple files 
     s shimp                     Produce .shimp (abbreviated Shimple) files 
     B baf                       Produce .baf files 
     b                           Produce .b (abbreviated Baf) files 
     G grimple                   Produce .grimple files 
     g grimp                     Produce .grimp (abbreviated Grimp) files 
     X xml                       Produce .xml Files 
     n none                      Produce no output 
     jasmin                      Produce .jasmin files 
     c class (default)           Produce .class Files 
     d dava                      Produce dava-decompiled .java files 
  -xml-attributes              Save tags to XML attributes for Eclipse 

There are six intermediate representations currently being used in Soot: baf, jimple, shimple, grimp, jasmin, and classfiles. A brief explanation of each form follows:

a streamlined representation of bytecode. Used to inspect Java bytecode as stack code, but in a much nicer form. Has two textual representations (one abbreviated (.b files), one full (.baf files).)

typed 3-address code. A very convenient representation for performing optimizations and inspecting bytecode. Has two textual representations (.jimp files, and .jimple files.)

an SSA variation of jimple. Has two textual representations (.shimp files, and .shimple files.)

aggregated (with respect to expression trees) jimple. The best intermediate representation for inspecting dissassembled code. Has two textual representations (.grimp files, and .grimple files.)

a messy assembler format. Used mainly for debugging Soot. Jasmin files end with ".jasmin".

the original Java bytecode format. A binary (non-textual) representation. The usual .class files.

Setting up your CLASSPATH and generating a Jimple file

Soot looks for classfiles by examining your CLASSPATH environment variable or by looking at the contents of the -soot-classpath command line option. Included in this lesson is the program. Download this file, compile it (using javac or other compilers), and try the following command in the directory where Hello.class is located.

> java soot.Main -f jimple Hello

This may or not work. If you get the following:

Exception in thread "main" java.lang.RuntimeException: couldn't find type: java.lang.Object (is your soot-class-path set properly?)

This means that a classfile is not being located. Either Soot can not find the Hello classfile, or it can not load the Java Development Kit libraries. Soot resolves classfiles by examining the directories in your CLASSPATH environment variable or the -soot-classpath command line option.

Potential problem #1: Soot can not locate the Hello classfile. To make sure that it can find the classfile "Hello", (1) add "." to your CLASSPATH or (2) specify "." on the command line.

To carry out (1) on UNIX-style systems using bash,

and on Windows machines,

and to do (2),

> java soot.Main --soot-classpath . -f jimple Hello

Potential problem #2: Soot cannot locate the class libraries. In this case, Soot will report that the type "java.lang.Object" could not be found.

Under JDK1.2, the class libraries do not need to be explicitly specified in the CLASSPATH for the Java Virtual Machine to operate. Soot requires them to be specified either on the CLASSPATH or in the soot-classpath command line option. Theoretically, this means adding the path to a "rt.jar" file to the CLASSPATH or the soot-classpath.

Locating the rt.jar file

It is usually in a directory of the form "$root/jdk1.2.2/jre/lib" where $root is "/usr/local" or some similarly named directory. If you can not find it, you can attempt a find command such as:

> cd /usr ; find . -name "rt.jar" -print

which may be able to locate it for you. Otherwise your best bet is to contact your system administrator.

Important note for Windows users

Note that as of release 1, Soot will treat drive letters correctly, but under Windows the path separator must be a backslash (1#1), not a forward slash.

Summing up, you must issue a command of the form:

> export CLASSPATH=.:/usr/local/pkgs/jdk1.2.2/jre/lib/rt.jar

or if you use the soot-classpath option which is more cumbersome:

> java soot.Main -f jimple --soot-classpath .:/usr/local/pkgs/jdk1.2.2/jre/lib/rt.jar Hello

Once your CLASSPATH is set up properly, you should get:

> java soot.Main -f jimple Hello
Transforming Hello...

The file called Hello.jimple should contain:

public class Hello extends java.lang.Object
    public void <init>()
        Hello r0;

        r0 := @this: Hello;
        specialinvoke r0.<java.lang.Object: void <init>()>();

    public static void main(java.lang.String[])
        java.lang.String[] r0; $r1;

        r0 := @parameter0: java.lang.String[];
        $r1 = <java.lang.System: out>;
        virtualinvoke $r1.< void println(java.lang.String
)>("Hello world!");

Generating jimple, baf, grimp for java.lang.String

By simple extrapolation, you should be able to now generate .b, .baf, .jimp, .jimple, .grimp, and .grimple files for any of your favorite classfiles. A particularly good test is a classfile from the JDK library. So a command like:

> java soot.Main -f baf java.lang.String

should yield a file java.lang.String.baf containing text of the form:

    public static java.lang.String valueOf(char[], int, int)
        word r0, i0, i1;

        r0 := @parameter0: char[];
        i0 := @parameter1: int;
        i1 := @parameter2: int;
        new java.lang.String;
        load.r r0;
        load.i i0;
        load.i i1;
        specialinvoke <java.lang.String: void <init>(char[],int,int)>;


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Soot overview/Disassembling classfiles

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