RFR: 8376472: Shenandoah: Assembler store barriers read destination memory despite the decorators [v2]

[Martin Doerr]

On Fri, 30 Jan 2026 10:16:19 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> The issue is really a correctness issue, and it readily manifests in Valhalla, which sometimes does the stores with `IS_DEST_UNINITIALIZED` set. Unfortunately, Shenandoah SATB barriers ignore this attribute, and attempt to read the memory at store address. At best it crashes the VM with the "oopness" asserts, at worst it feeds "garbage" pointers into SATB machinery, which then wrecks havoc on everything else.
>> 
>> We need to make sure store barriers are consistently checking these attributes. Unfortunately, that would mean doing the changes in arch-specific assembler code. 
>> 
>> This PR makes sure the ShenandoahBarrierSetAssembler store barriers are roughly in the same shape, and that they consult `ShenandoahBarrierSet::need_*_barrier` to make the proper decisions whether to use SATB/card barriers.
>> 
>> `hotspot_gc_shenandoah` is enough to sanity-check this patch, but I am also running `all` tests for extra safety.
>> 
>> Additional testing:
>>  - [x] Linux x86_64 server fastdebug, `hotspot_gc_shenandoah`
>>  - [x] Linux AArch64 server fastdebug, `hotspot_gc_shenandoah`
>>  - [x] Linux x86_64 server fastdebug, `all` + `-XX:+UseShenandoahGC`
>>  - [x] Linux AArch64 server fastdebug, `all` + `-XX:+UseShenandoahGC`
>>  - [x] Linux {PPC64, RISC-V, S390X} server fastdebug, cross-compilation
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:
> 
>  - Missing return in PPC64 for non-reference stores
>  - Merge branch 'master' into JDK-8376472-shenandoah-store-barriers
>  - More polish
>  - RISC-V version
>  - More touchups, AArch64 version
>  - Store barrier cleanup

Marked as reviewed by mdoerr (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/29444#pullrequestreview-3727470494