Assembler and Disassembler for Java class files

The ProGuard Assembler and Disassembler can assemble and disassemble Java class files.

The disassembler takes class files and converts them to readable jbc (Java ByteCode) files, following the ProGuard Assembly Language specification.

The assembler does the opposite; it takes readable jbc files and converts them to class files.

Usage

The program is distributed as a single executable jar file that serves both as an assembler and as a disassembler. When the program detects a jbc file as input, it assembles it. Vice versa, when it detects a class file, it disassembles it. It can handle any combination of both; a jar file containing both jbc files and class files will have its jbc files assembled in the output and its class files disassembled in the output.

bin/assembler [<classpath>] <input> <output>

The input and the output can be .class/.jbc/.jar/.jmod files or directories, where .jbc files contain disassembled Java bytecode.

The classpath (with runtime classes and library classes) is only necessary for preverifying assembled code.

Example

As a small test, you can let the program disassemble itself:

bin/assembler lib/assembler.jar disassembled

The program will create a disassembled directory with readable files disassembled from the input jar. You can then let the program assemble the assembly files again:

bin/assembler /usr/lib/jvm/java-12-oracle/jmods/java.base.jmod disassembled assembled.jar

The program will now create an assembled.jar file with reassembled class files. It will use the jmod file as a run-time library to properly preverify the code.

Preverification

The ProGuard Assembly Language contains some syntactic sugar, notably for the StackMap and StackMapTable attributes. As of Java version 7, each Code attribute must contain a StackMapTable attribute. Since it would be very cumbersome to write these attributes by hand, the assembler automatically preverifies every method using the ProGuard preverifier, and creates the StackMapTable using the preverification info. As a consequence, the assembler needs to know the location of any library jars when assembling class files.

Downloads

The code is written in Java, so it requires a Java Runtime Environment (JRE 1.8 or higher).

You can download the assembler and disassembler in various forms:

• Pre-built artifacts at Maven Central
• A Git repository of the source code at Github

Building

If you've downloaded the source code, you can build it with Gradle:

./gradlew clean assemble

Once built, you can run the assembler and disassembler with the script bin/assembler.sh or bin/assembler.bat.

Using as a library

You can use the ProGuard assembler or disassembler from your own code by adding a dependency on the ProGuard assembler library. For a more complete example, see the CLI project (pga-cli).

import com.guardsquare.proguard.assembler.io.JbcReader
import proguard.classfile.ClassPool
import proguard.classfile.VersionConstants.CLASS_VERSION_1_6
import proguard.classfile.attribute.visitor.AllAttributeVisitor
import proguard.classfile.util.ClassReferenceInitializer
import proguard.classfile.util.ClassSuperHierarchyInitializer
import proguard.classfile.visitor.AllMethodVisitor
import proguard.classfile.visitor.ClassPoolFiller
import proguard.classfile.visitor.ClassVersionFilter
import proguard.io.ClassDataEntryWriter
import proguard.io.DataEntryNameFilter
import proguard.io.DataEntryReader
import proguard.io.DataEntryWriter
import proguard.io.FileSource
import proguard.io.FilteredDataEntryReader
import proguard.io.FixedFileWriter
import proguard.io.IdleRewriter
import proguard.io.RenamedDataEntryWriter
import proguard.io.util.IOUtil
import proguard.preverify.CodePreverifier
import proguard.util.ConcatenatingStringFunction
import proguard.util.ConstantStringFunction
import proguard.util.ExtensionMatcher
import proguard.util.SuffixRemovingStringFunction
import java.io.File


fun main(args: Array<String>) {
    // Read a JBC file and write a class file
 
    val inputSource = FileSource(File(args[0]))

    val programClassPool = ClassPool()
    val libraryClassPool = if (args.size > 2) IOUtil.read(args[2], true) else ClassPool()

    val jbcReader: DataEntryReader = JbcReader(
        ClassPoolFiller(programClassPool)
    )

    val reader: DataEntryReader = FilteredDataEntryReader(
        DataEntryNameFilter(ExtensionMatcher(".jbc")), jbcReader
    )

    inputSource.pumpDataEntries(reader)

    // Preverify before writing the class
    preverify(programClassPool, libraryClassPool)

    val outputFile = File(args[1])
    val writer = FixedFileWriter(outputFile)

    val jbcAsClassWriter: DataEntryWriter = RenamedDataEntryWriter(
        ConcatenatingStringFunction(
            SuffixRemovingStringFunction(".jbc"),
            ConstantStringFunction(".class")
        ),
        ClassDataEntryWriter(programClassPool, writer)
    )

    // Write the class file by reading in the jbc file and 
    // replacing it using the `IdleRewriter`.
    inputSource.pumpDataEntries(
        FilteredDataEntryReader(
            DataEntryNameFilter(ExtensionMatcher(".jbc")),
            IdleRewriter(jbcAsClassWriter)
        )
    )

    writer.close()
}

fun preverify(libraryClassPool: ClassPool, programClassPool: ClassPool) {
    programClassPool.classesAccept(ClassReferenceInitializer(programClassPool, libraryClassPool))
    programClassPool.classesAccept(ClassSuperHierarchyInitializer(programClassPool, libraryClassPool))
    libraryClassPool.classesAccept(ClassReferenceInitializer(programClassPool, libraryClassPool))
    libraryClassPool.classesAccept(ClassSuperHierarchyInitializer(programClassPool, libraryClassPool))
    programClassPool.classesAccept(
        ClassVersionFilter(
            CLASS_VERSION_1_6,
            AllMethodVisitor(
                AllAttributeVisitor(
                    CodePreverifier(false)
                )
            )
        )
    )
}

Contributing

The ProGuard Assembler and Disassembler are build on the ProGuardCORE library.

Contributions, issues and feature requests are welcome in both projects. Feel free to check the issues page and the contributing guide if you would like to contribute.

License

The ProGuard Assembler and Disassembler are distributed under the terms of the Apache License Version 2.0.

Enjoy!

Copyright (c) 2002-2022 Guardsquare NV