Integrated: 8253860: PPC: Relocation::pd_set_data_value conflates compressed oops and klasses

[Martin Doerr]

On Mon, 6 Dec 2021 09:29:45 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

> Casting narrow Klass pointer to a narrow Oop is problematic. Note that `NativeMovConstReg::set_narrow_oop` only supports narrow Oops.
> It turns out, that the problematic code is unused. We never patch narrow Klass pointers in the instruction stream on PPC64 (`metadata_Relocation::pd_fix_value` has an empty implementation). In contrast to that, narrow Oops in the instructions stream always get patched when the nmethod gets installed (by `fix_oop_relocations`). This makes sense as Metadata doesn't get relocated, but Oops may be moved by GC and the instructions need to get the current value during nmethod installation.
> Note that the initial constants we were using for narrow Oops in the instruction stream were not correct (Oop compression missing, not updated by GC). So, I think it's better to use 0 to avoid confusion.

This pull request has now been integrated.

Changeset: 01b30bfa
Author:    Martin Doerr <mdoerr at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/01b30bfa99e95cf1e9209c8de1f3c3c762596708
Stats:     39 lines in 5 files changed: 1 ins; 24 del; 14 mod

8253860: PPC: Relocation::pd_set_data_value conflates compressed oops and klasses

Reviewed-by: dlong, rrich

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PR: https://git.openjdk.java.net/jdk/pull/6716