[lworld] RFR: 8341771: [lworld] Heap dump recognizing new flat fields formats [v2]

[Frederic Parain]

On Wed, 5 Nov 2025 21:50:58 GMT, Alex Menkov <amenkov at openjdk.org> wrote:

>> The fix re-implements flat object support in heap dumper.
>> New approach does not require changes in .hprof format.
>> Flat value objects are dumped as heap-allocated objects with generated ID.
>> For heap-allocated objects the ID is their address (oop), they are always aligned.
>> ID generator for flat objects uses unaligned values (so there is no conflicts with oops).
>> 
>> HeapDump test was reimplemented (it was disabled for a long time)
>> Changes in hprof test lib were reverted (they are not needed anymore)
>> 
>> testing: tier1..4,hs-tier5-svc
>
> Alex Menkov has updated the pull request incrementally with one additional commit since the last revision:
> 
>   removed T_FLAT_ELEMENT in StackRefDumper

src/hotspot/share/services/heapDumper.cpp line 1445:

> 1443:   int type_size;
> 1444:   if (type == T_OBJECT || type == T_FLAT_ELEMENT) {
> 1445:     type_size = sizeof(address);

Array elements size is not always sizeof(address) for flat arrays (could be smaller or bigger).
The real size of the array elements can be retrieved using the element_byte_size() method in FlatArrayKlass.

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1700#discussion_r2499197064