Release NotesAsmTools 9.1January 2026 |
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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.
| 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 |
| 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 |
Using ASM Tools requires a properly configured, certified ava Platform, Standard Edition version 17 or later
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.
| Component | Description |
|---|---|
| README.html | The AsmTools release notes (this document). |
| lib/asmtools.jar | The AsmTools library. |
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.)
There are no operating modes.
Many attributes (in the class file, as specified by the Java VM Specification, Chapter 4) are covered in the JASM syntax, but not all.
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.
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/asmtoolsThis 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.
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:
The general steps to take a build from source from the command line:
<topdir>/build/
% ant
../../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 antThis 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)