In a discussion on jdk-dev, Jorn Vernee suggested that two large FFM tests can be generated at build time:

https://mail.openjdk.org/pipermail/jdk-dev/2024-October/009559.html

This relates to these two files:
6.8M ./test/jdk/java/foreign/libTestUpcallStack.c
3.5M ./test/jdk/java/foreign/libTestDowncallStack.c

which are generated by test/jdk/java/foreign/CallgeneratorHelper.java.

(He also added: "FWIW, we have other examples of test code that is generated by scripts as well, such as test/jdk/java/lang/invoke/VarHandles/generate-vh-tests.sh and various scripts under test/jdk/java/nio/Buffer which invoke SPP. There are probably more cases like that.")

The first step here is enabling gensrc for native tests; then we can look at the particulars for CallgeneratorHelper.