local-test-commons-compress-full-01-vuln_0/fuzz-tooling/infra/experimental/chronos/README.md

Chronos: rebuilding OSS-Fuzz harnesses using cached builds

Pre-built images.

Daily pre-built images are available at:

• us-central1-docker.pkg.dev/oss-fuzz/oss-fuzz-gen/<PROJECT>-ofg-cached-address
• us-central1-docker.pkg.dev/oss-fuzz/oss-fuzz-gen/<PROJECT>-ofg-cached-coverage

They can be used as drop-in replacements for the usual gcr.io/oss-fuzz/<PROJECT> images.

These images are generated in 2 ways:

• (Preferred) Generate a replay build script that can be re-run alongside existing build artifacts, leveraging existing build system mechanisms to avoid rebuilding (e.g. running make twice should not actually rebuild everything). This is error-prone, so we validate the script works by running it.
• (Fallback, if the replay build script didn't work). We leverage ccache, to provide a compiler cache. This is often not as fast as the replay build script, because some project builds spend significant time doing non-compiler tasks (e.g. checking out submodules, running configure scripts).

Note: this mechanism does not work for every single OSS-Fuzz project today. The resulting image may either:

• Not provide much performance improvement compared with a normal image, or
• Not exist at all (if neither approach worked).

Stats from a recent run: https://gist.github.com/oliverchang/abaf3a1106a2b923c0ac3a577410aaaa (Feb 3 2025).

Usage locally

Example 1: htslib

From the OSS-Fuzz root

$ RUN_ALL=1 ./infra/experimental/chronos/build_cache_local.sh htslib c address
...
...
Vanilla compile time:
17
Replay worked
Replay compile time:
2
Ccache compile time: 
9