[master] RFR: 8347710: [Lilliput] Implement 4 byte headers [v8]

[Thomas Stuefe]

On Tue, 16 Sep 2025 21:44:01 GMT, Cesar Soares Lucas <cslucas at openjdk.org> wrote:

>> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix build
>
> src/hotspot/share/jvmci/jvmciCompilerToVM.cpp line 454:
> 
>> 452:   const char* base_desc = nullptr;
>> 453:   JVMCIKlassHandle klass(THREAD);
>> 454:   if (offset == 1 /*oopDesc::klass_offset_in_bytes()*/) {
> 
> @rkennke I'm seeing a crash internally in Graal and I'm suspecting that this line may be the culprit. The error is:
> 
> 
> Caused by: java.lang.IllegalArgumentException: Unexpected arguments: Ljdk/vm/ci/hotspot/DirectHotSpotObjectConstantImpl; 8 true
> 	at jdk.internal.vm.ci/jdk.vm.ci.hotspot.CompilerToVM.getResolvedJavaType0(Native Method)
> 	at jdk.internal.vm.ci/jdk.vm.ci.hotspot.CompilerToVM.getResolvedJavaType(CompilerToVM.java:1020)
> ...
> 
> I'm wondering if the commented part of the condition was supposed to be uncommented at some point.

Did you really intend to use *4-byte* headers in Graal, e.g., as an experiment? This is still a work-in-progress (albeit quite progressed). The official Lilliput was merged into mainline; the lilliput repo now contains the ongoing 4-byte header work.

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PR Review Comment: https://git.openjdk.org/lilliput/pull/193#discussion_r2359750856