Reproducible Builds at Eclipse Adoptium

Why do we need Reproducible Builds?

Confidence in the high quality of the process to create the binaries

Being able to repeatably build the same OpenJDK source in an identical manner, producing identical JDK binaries, shows confidence and quality in the production process. The necessity for producing identical results is to know exactly what is going into the binary and the exact repeatability of the build process, through what source and dependencies are used, to what compiler tooling is used. The fact that a reproducible identical JDK binary can only be achieved by all these stringent controls, shows the high quality of the processes used to bring the JDK binaries to the consumers.

Secure Supply Chain

The reproduciblity of builds goes hand in hand with knowing exactly what goes into it, in other words the Software Bill of Materials (SBOM). This detailed knowledge means we know the source and provenance of everything within and used to build the JDK. Thus any publicly published CVEs or vulnerabilities can be quickly cross-checked with the JDK and build tooling used. For more information on SBOM’s and their capabilities see CycloneDX.

The other aspect of a secure supply chain is being able to absolutely identify a JDK binary as being secure, this is especially true for Open Source community projects. The ability to repeatedly recreate a JDK binary identically from the Adoptium build scripts provides a mechanism to achieve this. The Adoptium releases can be re-built within multiple secure environments each with stringent bill of material checks, and then the binaries compared to ensure byte for byte identical output. If the builds from the multiple secure environments are identical to the one from the open-source projects, the likelihood of malicious tampering would be extremely low.

Better consumer support capabilities for releases

Reproducibility necessitates a Software Bill of Materials (SBOM), from the secure hashes (SHAs) of all the component parts, to the versions and SHAs of dependent components and the tooling used to build it. This means any requirement to re-build with a specific patch can be sure to be rebuilt with the exact same source and tooling, with just that one patch added. Also any support queries on known bugs or issues in any component or build tool can be cross checked with the SBOM for any given release to determine if they are affected.

Best practices for a Secure Software Development Framework (SSDF)

The Secure Software Development Framework SSDF identifies a standard for best practices for organizations to prepare, protect, and secure their software delivery processes. The advantages provided by “Reproducible Builds” and “Software Bill of Materials” are placed in many of the best practices identified within this standard.

Improved Adoptium Build Script Validation

One aspect of a continually changing and improving open source community is ensuring any changes are good with no side effects. For example ensuring changes to build scripts don’t alter the JDK binary when they should not. A guaranteed way of assuring that such changes do not, is to leverage reproducible builds. Simply comparing the JDK binary output from before and after a build script change, and checking they are identical, proves the change has not had any unforeseen effect.

The progress at Eclipse Adoptium to achieve Reproducible Builds

OpenJDK upstream contributions

The OpenJDK upstream community is fully supportive of reproducible builds, and over the past year many contributors have been finding and resolving non-deterministic issues. At Eclipse Adoptium extensive work has been done to achieve identical OpenJDK binaries on the Linux platforms in the jdk “head” stream (jdk-19+). This has involved in-depth build comparison debugging to identify non-deterministic build issues, and any OpenJDK issues are then contributed back upstream to the OpenJDK community project. These fixes have also been backported to the jdk17u stream, since jdk-17 is a long term supported release.

OpenJDK contributions:

Ongoing Eclipse Adoptium Reproducible Build projects

As well as continuing to identify and fix any OpenJDK non-deterministic issues, Eclipse Adoptium is continuing to integrate changes into the build scripts to fully support reproducible builds.

The following capabilities are available at Eclipse Adoptium:

  • Reproducible jdk-19 builds for all Temurin Linux architectures

The following are projects currently in-progress:

Future projects:


Today’s Enterprise Software needs to be more secure and safe from vulnerability attacks than ever before. Providing methods for ensuring the security of the supply chain and ways of demonstrating the quality of the products delivered are essential. The Eclipse Adoptium reproducible build and SBOM integration is providing these essemtial features for the community.

If your company is working on reproducible builds, or other methods for securing your supply chains, how are you approaching this problem? How would your organization leverage Eclipse Adoptium reproducible builds?

Feedback and contributions to this initiative are most welcome.

Do you have questions or want to discuss this post? Hit us up on the Adoptium Slack workspace!

Posted by Andrew LeonardAdoptium Build team member working for Red Hat