Building/distributing more than one VM in a single JDK distribution

[Aleksei Voitylov]

Hi Magnus,

thank you for elaborating on the new possible configure option 
semantics. We'll be happy to see this as a replacement.

-Aleksei

On 13.03.2025 18:20, Magnus Ihse Bursie wrote:
> Hi all,
>
> I hear that there are still relevant use cases to be able to 
> distribute more than JVM and let the user select which one to use -- 
> either directly for debugging purposes (Shipilev's use case), or by 
> selecting which to include in a final jpackage (your use case).
>
> On 2025-03-12 12:52, Aleksei Voitylov wrote:
>
>> On the other hand, I share your concern for build system complexity. 
>> Maybe what could be done is create a build step that will, once 
>> several VMs are built from the same codebase sequentially, merge them 
>> into one build? This would invovle patching java.base at this last 
>> step (which I don't particularly like). But if this is something that 
>> will simplify the build process, I'm all for it. That would allow 
>> distributions that ship such multi-VM bundles to keep doing so.
>
> My thinking is that I should add a new configure option, 
> --with-import-jvms=zero:/builddir/build-with-zero/hotspot/lib/libjvm.so,minimal:/builddir/build-with-minimal/hotspot/lib/libjvm.so, 
> or something like that.
>
> That means no patching is needed, and if you want to build a JDK with 
> multiple JVMs, all you need to do is to like:
>
> configure --with-conf-name=build-with-zero --with-jvm-variant=zero && 
> make hotspot
> configure --with-conf-name=build-with-minimal 
> --with-jvm-variant=minimal && make hotspot
>
> and then you can do
>
> configure 
> --with-import-jvms=zero:/builddir/build-with-zero/hotspot/lib/libjvm.so,minimal:/builddir/build-with-minimal/hotspot/lib/libjvm.so 
> && make jdk-image
>
> This would essentially just copy the relevant hotspot libraries in the 
> correct place, and update jvm.cfg. No patching of java.base or such 
> thing would be needed, and the build speed would be essentially 
> unchanged. The only downside is a slight complication for the build 
> scripts, but I think that would be livable.
>
> /Magnus