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slicer docs

Disassembly

Disassembly is a reconstruction of a Java class file into a human-readable representation or into Java source code (decompilation), this is the main view you’ll see in slicer.

The currently supported disassemblers/decompilers are:

Custom ones can be added through the Disassembler API (popular ones are here).

Integrated disassembler

slicer includes a basic disassembler to power several bytecode analysis features, such as:

  • the class view (prettifying class file constructs)
  • the flow graph (prettifying instructions and computing the graph itself)
  • the search (prettifying constant pool entries)
  • the pseudocode disassembler

Constant pool

Constant pool entries are represented in a format consisting of the entry type identifier and the stringified value of the entry.

  • UTF8 <value> - any string-like value defined in the class file (names, descriptors, strings, …)
  • INTEGER/FLOAT/LONG/DOUBLE <value> - primitives defined in the class file
  • CLASS <class name in internal format, UTF8 value> - class reference
  • STRING "<UTF8 value>" - string literal defined in the class file
  • METHOD_TYPE <method descriptor, UTF8 value> - method descriptor reference
  • MODULE/PACKAGE <module/package name, UTF8 value> - module-info/package-info name data
  • FIELDREF/METHODREF/INTERFACE_METHODREF <owner name, CLASS value> <member name and descriptor, NAME_AND_TYPE value> - class member reference
  • NAME_AND_TYPE <name, UTF8 value> <descriptor, UTF8 value> - member name and descriptor reference
  • DYNAMIC/INVOKE_DYNAMIC <bootstrap method index> <member name and descriptor, NAME_AND_TYPE value>
  • METHOD_HANDLE <handle kind> <METHODREF value>
    • handle kinds: GET_FIELD, GET_STATIC, PUT_FIELD, PUT_STATIC, INVOKE_VIRTUAL, INVOKE_STATIC, INVOKE_SPECIAL, NEW_INVOKE_SPECIAL, INVOKE_INTERFACE

Pseudocode

The disassembler produces pseudocode similar to Java, which allows you to view the rough structure of classes in a familiar way.

It does not resugar many code constructs, such as if statements and variable declarations, so knowledge of the JVM instruction set is highly necessary.

// Source file: StringsDuplicates.java
package sample.string;


public super class StringsDuplicates extends java.lang.Object {
    private static final java.lang.String F = "Hello this is a duplicate string";


    public StringsDuplicates() {
        // 0: aload this Lsample/string/StringsDuplicates;
        // 1: invokespecial java/lang/Object <init> ()V
        // 4: return
    }
    public static void main(java.lang.String[] args) {
        //  0: ldc "Hello this is a duplicate string"
        //  2: astore s Ljava/lang/String;
        //  3: ldc "Hello this is a duplicate string"
        //  5: invokestatic sample/string/StringsDuplicates p (Ljava/lang/String;)V
        //  8: aload s Ljava/lang/String;
        //  9: invokestatic sample/string/StringsDuplicates p (Ljava/lang/String;)V
        // 12: invokestatic sample/string/StringsDuplicates duplicate ()Ljava/lang/String;
        // 15: invokestatic sample/string/StringsDuplicates p (Ljava/lang/String;)V
        // 18: ldc "Hello this is a duplicate string"
        // 20: invokestatic sample/string/StringsDuplicates p (Ljava/lang/String;)V
        // 23: return
    }
    private static java.lang.String duplicate() {
        // 0: ldc "Hello this is a duplicate string"
        // 2: areturn
    }
    public static void p(java.lang.String s) {
        // 0: getstatic java/lang/System out Ljava/io/PrintStream;
        // 3: aload s Ljava/lang/String;
        // 4: invokevirtual java/io/PrintStream println (Ljava/lang/String;)V
        // 7: return
    }
}

Dissecting the class header, we can make out that we’re looking at a regular class named StringsDuplicates with the modifiers ACC_PUBLIC and ACC_SUPER, and a super class of java.lang.Object.

Furthermore, it’s located in the sample.string package and was compiled from a StringsDuplicates.java source file.

// Source file: StringsDuplicates.java
package sample.string;


public super class StringsDuplicates extends java.lang.Object {
    // ...
}

Members

Our class contains a couple of methods and one self-explanatory field, with one method resugared to its original constructor syntax. The field has an assigned value, showing a value from its ConstantValue attribute.

Code inside the methods is represented via string representations of individual instructions and their offsets.

Instructions may also be encased in a try-catch statement with a virtual goto in the handler, signifying an entry in the exception handler table.

// ...
private static final java.lang.String F = "Hello this is a duplicate string";


public StringsDuplicates() {
    // 0: aload this Lsample/string/StringsDuplicates;
    // 1: invokespecial java/lang/Object <init> ()V
    // 4: return
}
public static void main(java.lang.String[] args) {
    //  0: ldc "Hello this is a duplicate string"
    //  2: astore s Ljava/lang/String;
    //  3: ldc "Hello this is a duplicate string"
    //  5: invokestatic sample/string/StringsDuplicates p (Ljava/lang/String;)V
    //  8: aload s Ljava/lang/String;
    //  9: invokestatic sample/string/StringsDuplicates p (Ljava/lang/String;)V
    // 12: invokestatic sample/string/StringsDuplicates duplicate ()Ljava/lang/String;
    // 15: invokestatic sample/string/StringsDuplicates p (Ljava/lang/String;)V
    // 18: ldc "Hello this is a duplicate string"
    // 20: invokestatic sample/string/StringsDuplicates p (Ljava/lang/String;)V
    // 23: return
}


// ...