RFR: 8353274: [PPC64] Bug related to -XX:+UseCompactObjectHeaders -XX:-UseSIGTRAP in JDK-8305895

[Martin Doerr]

On Thu, 3 Apr 2025 13:36:26 GMT, Richard Reingruber <rrich at openjdk.org> wrote:

> I've been looking for more references to `oopDesc::klass_offset_in_bytes()` and found
> 
> https://github.com/openjdk/jdk/blob/296d9d6f7a734cc2bab21c58f21a941150b4cf2a/src/hotspot/cpu/ppc/c2_MacroAssembler_ppc.cpp#L54
> 
> 
> To me it looks like neither on aarch64 nor on x86 `oopDesc::klass_offset_in_bytes()` needs to be deducted from the address. Why is it done on ppc64?

The other platforms had the same implementation in an earlier version. It was simplified in a way which doesn't work on Big Endian platforms. That's why PPC64 still has the old implementation. See https://github.com/openjdk/jdk/pull/22078#issuecomment-2479943053

Thanks for the review! I think this PR is simple enough to go in with only 1 review. It only touches PPC64 code.

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PR Comment: https://git.openjdk.org/jdk/pull/24331#issuecomment-2776067206