Java Bytecode Reducer

This project contains a test case reducer for Java bytecode in the spirit of C-Reduce. It provides multiple modules that apply different reduction techniques to selected bytecodes in order to remove complex instruction sequences and unused members.

Usage

To initiate a reduction sequence, the following command line options are supported:

jreduce [-d <arg>] [-f <arg>] [-help] [-i <arg>] [-k] [-l] [-out <arg>] [-q | -v] [-t <arg>] [-tmp <arg>] [-version]

Argument	Description
-d,--working-dir	The working directory in which the task is run (if omitted, the current directory is assumed)
-f,--filter	Choose individual operations or modules to apply
-help,--help	Display information about application usage
-i,--i-tests	The interestingness test file (test.{sh,bat} is assumed if no argument is supplied)
-k,--keep	Keep temporary test directories and files
-l,--list-modules	List all available transformation modules
-out,--out-dir	The directory where results will be placed
-q,--quiet	Suppress log messages
-t,--timeout	The timeout in seconds until runs of the test files are interrupted (to prevent infinite loops)
-tmp,--temp-dir	The temporary directory where the intermediate test results will be placed
-v,--verbose	Verbose logging
-version,--version	Print program version

Supported modules

• Fields

  • Remove all field attributes

    Attempts to strip fields of all their attributes (effectively making them package-protected instance variables)

  • Remove random field attributes

    Attempts to randomly remove field attributes (e.g. STATIC, FINAL, PRIVATE)

  • Remove read-only fields

    Removes fields that are only read and never updated (except initial assignment in constructor / initializer)

  • Remove static field attributes

    Attempts to remove static attributes of fields (making them instance variables)

  • Remove unused fields

    Searches for fields that are never used (except in initial assignment) and removes them

  • Remove write-only fields

    Searches for fields that are only updated but never queried and remove them

• Methods

  • Remove all method attributes

    Strips all attributes of a method (effectively making them package-protected instance methods)

  • Remove empty methods

    Removes (void) methods that only consist of return instructions

  • Remove initializers

    Removes constructors and static initializers (skipping the implicitly created default constructor)

  • Remove random method attributes

    Attempts to randomly remove a method attribute (e.g. STATIC, FINAL, SYNCHRONIZED)

  • Remove unused methods

    Searches for methods that are never called and removes them - this includes self-recursions i.e.

    public void aMethod() {
      aMethod();
    }
    

  • Remove void method calls

    Randomly removes call sites of void methods

  • Replace method calls

    Replaces non-void method call sites with assignments to default values - i.e.

    int i = getInt();
    // becomes
    int i = 0;
    

• Control flow

  • Remove constant assignments

    This low-level module removes consecutive constant assignments - i.e.

    iconst_0
    istore_0
    

  • Remove instruction sequences

    This low-level module keeps track of the stack size and removes instruction sequences that start at and then again lead to an empty stack

  • Remove stack-neutral instructions

    Low-level module that removes (replaced with nop) single instructions that do not change the stack level (even if they push and pop elements)

• Miscellaneous

  • Shrink constant pool

    Removes elements from the constant pool that are no longer referenced

  • Remove NOPs

    Removes any remaining nop from the bytecode

Installation

To run the tool, the project has to be downloaded or cloned. Using the provided Gradle Wrapper, it is possible to run the tool by executing

./gradlew run --args='<args>' (Linux)

./gradlew.bat run --args='<args>' (Windows)

from within the application directory.

Additionally, it is also possible to generate a JAR from the sources by executing

./gradlew jar (Linux)

./gradlew.bat jar (Windows)

This generates the executable JAR file ./build/libs/jreduce.jar, which in turn can be run using

java -jar jreduce.jar <args>

Examples

The samples folder contains both class file samples and corresponding interestingness tests for both Windows and Linux.