README - AsmTools - Version 9.1

# Release Notes ## AsmTools 9.1 ## January 2026

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## Table of Contents

Introduction
New in This Release
System Requirements
Release Contents
Installation
Using AsmTools
Known Bugs and Issues
Obtaining Sources
Building from Sources
Contribute

## Introduction

AsmTools is a software package containing a collection of tools that you can use to encode and decode a Java class file, without using a Javac compiler. You can use AsmTools to create class files which can not normally be produced by a compiler. These class files can be used during the development process to test the compliance of a Virtual Machine (VM) to its specification.

These release notes contain information about the ASM Tools version 9.1.
See the ( CodeTools project) AsmTools OpenJDK project page for more information about AsmTools.

## New in This Release

### New Features

Bug ID | Description
--- | ---
CODETOOLS-7904123 | Switch the Asmtools build system to use JDK 17 (LTS) in alignment with jtreg
CODETOOLS-7903806 | Enhance jasm/jdis to support value classes and objects

### Fixed Bugs

Bug ID | Description
--- | ---
CODETOOLS-7902055 | Preserve module name in jdec output
CODETOOLS-7904095 | jdis,jasm: tools that read or write reference types may corrupt Constant Pool entries
CODETOOLS-7904065 | Classfile version < 45 synthetic methods should not set ACC_SYNTHETIC
CODETOOLS-7904032 | jasm: Incorrectly processes empty SourceDebugExtension attribute
CODETOOLS-7904019 | jdis: Incorrectly processes lookupswitch, wide, and tableswitch instructions with an incorrect structure
CODETOOLS-7904014 | jasm: the jasm incorrectly parses the PermittedSubclasses/NestMembers attribute
CODETOOLS-7902696 | jdis: the tool does't catch circular references in bsm args

## System Requirements

Using ASM Tools requires a properly configured, certified ava Platform, Standard Edition version 17 or later

## Installation

To install the AsmTools, simply unzip the asmtools-9.1.zip distribution file in the directory of your choice. Optionally, you may wish to define an environment variable (ASMTOOLS_HOME) to point to this location for your convenience.

## Release Contents

This section lists the components under the base subdirectory structure (`asmtools-9.1/`) that is created when you unzip the AsmTools distribution archive during installation.

### Important Component Descriptions and Locations

Component | Description
--- | ---
`README.html` | The AsmTools release notes (this document).
`lib/asmtools.jar` | The AsmTools library.

## Using AsmTools

AsmTools have the following synopsis:

    java -jar ${ASMTOOLS_HOME}/asmtools.jar TOOL FILE
       [TOOL="jasm" | "jdis" | "jcoder" | "jdec"]
       [FILE=FILENAME.jasm (for jasm command) | FILENAME.jcod (for jcod command) | FILENAME.class for jdis, jdec command]

Examples:

      % java -jar ${ASMTOOLS_HOME}/asmtools.jar jasm -d . FILENAME.jasm
      (Produces FILENAME.class in the current directory.)

      % java -jar ${ASMTOOLS_HOME}/asmtools.jar jdis FILENAME.class
      (Prints FILENAME.jasm to stdout.)

      % java -jar ${ASMTOOLS_HOME}/asmtools.jar jcoder -d . FILENAME.jcod
      (Produces FILENAME.class in the current directory.)

      % java -jar ${ASMTOOLS_HOME}/asmtools.jar jdec -d . FILENAME.class
      (Produces FILENAME.jcod in the current directory.)

Tool usage is covered in the "Using AsmTools".

### Operating Modes

There are no operating modes.

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## Known Bugs and Issues

Many attributes (in the class file, as specified by the Java VM Specification, Chapter 4) are covered in the JASM syntax, but not all.

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## Contribute

The AsmTools open source project was created in order to develop a community that will improve it, further the development of Java assembly tools, and use Java assemblers to develop test suites. We encourage you to browse, download, contribute, and get involved.

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## Obtaining the Sources

The sources for ASM Tools 9.1 and later is available via the community OpenJDK project. The sources are stored and accessed through a Mercurial repository, which the public may access in a read-only fashion. Committing to changes to the sources is accomplished by first contributing through a proxy developer to establish ones self, which can then lead to rights to contribute directly. More information can be found on the OpenJDK Projects landing page.

The general form for obtaining a copy of the current source tree is:

    % git clone https://github.com/openjdk/asmtools

This places a copy of the entire source tree in the asmtools directory. From that directory, you can then view and build the sources, as described in the next section. Note that this copy is of the development version of the sources, you may need to extract a different revision if you want a copy from a specific period of time.

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## Building the Sources

Building the sources requires Ant version 1.8 or later (1.10.13 is current at the time of writing), and the built-in build is compatible with using an IDE. The sources are designed for Java 17 and if you invoke `ant` with this runtime, your chance of encountering an abnormal conditions due to your runtime or compiler (or javadoc) version.

General requirements:

- ant, version 1.8 or later
- Java 17 runtime and compiler (minimum and recommended)
- 10MB free disk space (3MB for source tree, 7MB for build output)

The general steps to take a build from source from the command line:

1. Obtain Sources
2. Make your current directory `<topdir>/build/`
3. Invoke ant:
   `% ant`
4. Output appears in a directory above (one above <topdir>), such as: `../../asmtools-9.1-build/`

A common variation of the build command to force `ant` to use a particular installation of Java on your machine:

    # JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk-17.jdk/Contents/Home ANTHOME=/usr/share/ant ant

This example for common *nix shells (`zsh, bash, sh`), alter it as needed for your command environment. You can test your invocation of `ant` by running it with the `-diagnostics` flag, where it will indicate which Java it is using.

The build file itself is `build/build.xml`, this is the file you can specify in your IDE for building.

Copyright © 2008, 2026, Oracle and/or its affiliates. All rights reserved.
Use is subject to license terms.The majority of the Assember Tools project is released under the GNU General Public License Version 2 (GPLv2)