RFR: 8339480: Build static-jdk image with a statically linked launcher [v7]

[Johan Vos]

On Tue, 15 Oct 2024 20:22:52 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> As a prerequisite for Hermetic Java, we need a statically linked `java` launcher. It should behave like the normal, dynamically linked `java` launcher, except that all JDK native libraries should be statically, not dynamically, linked.
>> 
>> This patch is the first step towards this goal. It will generate a `static-jdk` image with a statically linked launcher. This launcher is missing several native libs, however, and does therefore not behave like a proper dynamic java. One of the reasons for this is that local symbol hiding in static libraries are not implemented yet, which causes symbol clashes when linking all static libraries together. This will be addressed in an upcoming patch. 
>> 
>> All changes in the `src` directory are copied from, or inspired by, changes made in [the hermetic-java-runtime branch in Project Leyden](https://github.com/openjdk/leyden/tree/hermetic-java-runtime).
>
> Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Don't hardcode server variant

I tried to build/run this on Linux as well (since I'm using parts of this PR in https://github.com/openjdk/mobile/pull/30) and I noticed that the executable doesn't start (even with --version):

images/static-jdk/bin/java --version
Error: Failed , because images/static-jdk/bin/java: undefined symbol: JNI_CreateJavaVM

The `JNI_CreateJavaVM` symbol seems to be local only:

nm images/static-jdk/bin/java |grep JNI_CreateJ
0000000000e22430 t JNI_CreateJavaVM

Hence calling it with `dlsym` won't work. And indeed, that is how it is called from `./java.base/unix/native/libjli/java_md.c ` `(LoadJavaVM)`

dlsym(libjvm, "JNI_CreateJavaVM");

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PR Comment: https://git.openjdk.org/jdk/pull/20837#issuecomment-2431273631