aotp — AOT Cache Parser

A tool to inspect and analyze HotSpot AOTCache (.aot) files.

The format is adapted for JDK 27+7 but also works well for JDK 25. Note that the value of access_flags is different and incorrect in JDK 25-created AOTCache files due to 8372098: Move AccessFlags to InstanceKlass.

Build

mvn package

Usage

Print file map header

java -jar aotp/target/aotp-0.0.1-SNAPSHOT.jar <cache.aot> --header

List instance classes in the AOTCache

java -jar aotp/target/aotp-0.0.1-SNAPSHOT.jar <cache.aot> --list-classes

List classes with a specific flag

For example, list classes that have had their <clinit> pre-executed:

java -jar aotp/target/aotp-0.0.1-SNAPSHOT.jar <cache.aot> --list-classes=aotClassFlags:has_aot_initialized_mirror

Multiple flags can be required (all must match):

java -jar aotp/target/aotp-0.0.1-SNAPSHOT.jar <cache.aot> --list-classes=aotClassFlags:has_aot_initialized_mirror,has_archived_enum_objs

Print details of a class

java -jar aotp/target/aotp-0.0.1-SNAPSHOT.jar <cache.aot> --print-class "java/lang/String"

Print class sizes

Caution

This may be wrong. See #9.

java -jar aotp/target/aotp-0.0.1-SNAPSHOT.jar <cache.aot> --class-size "java/lang/String" "java/lang/Object"

Print constant pools

Print all constant pools:

java -jar aotp/target/aotp-0.0.1-SNAPSHOT.jar <cache.aot> --list-constant-pools

Print one class's constant pool:

java -jar aotp/target/aotp-0.0.1-SNAPSHOT.jar <cache.aot> --list-constant-pools="org/apache/pdfbox/tools/TextToPDF"

Integrity check

Verify that an AOT cache was built from a specific set of JARs. Detects version mismatches (stale cache after a dependency upgrade) and tampered caches (injected symbols).

java -jar aotp/target/aotp-0.0.1-SNAPSHOT.jar <cache.aot> --check-integrity lib1.jar lib2.jar ...

The report has three sections:

• matched — classes present in both the JARs and the AOT cache with identical constant pool symbols
• mismatched — classes whose constant pool differs; each entry shows missingSymbols (in JAR but absent from AOT) and addedSymbols (in AOT but absent from JAR, indicating injection or a version change)
• stale — application classes in the AOT cache with no corresponding class in the supplied JARs

The check uses constant pool Utf8 entries (method/field names, type descriptors, string literals) as the comparison unit. If a method signature or class reference changed, the descriptor Utf8 changes and is caught here.

Related Work

Java AOT Cache Diagnostics Tool