[lworld] RFR: 8366717: [lworld] Cleanup defensive fixing of JDK-8365996 [v2]

[Tobias Hartmann]

On Fri, 19 Dec 2025 08:44:08 GMT, Marc Chevalier <mchevalier at openjdk.org> wrote:

>> Let's proceed piece by piece.
>> 
>> # `G1BarrierSetAssembler::g1_write_barrier_pre` in `g1BarrierSetAssembler_aarch64.cpp`
>> 
>> https://github.com/openjdk/valhalla/blob/1077e4f9f06336af30d95fc28cbab4d31c9f2a44/src/hotspot/cpu/aarch64/gc/g1/g1BarrierSetAssembler_aarch64.cpp#L216-L220
>> 
>> `push_call_clobbered_registers`/`pop_call_clobbered_registers` should be enough around a runtime call, that's what clobbered registers are.
>> 
>> But let's dig a bit, that will be useful later!
>> 
>> 
>>    push_call_clobbered_registers()
>> => push_call_clobbered_registers_except(exclude = empty set)
>> => push(call_clobbered_gp_registers() - exclude, sp)  // with exclude = empty set
>> 
>> So, we save at least `call_clobbered_gp_registers` which is defined as:
>> 
>> https://github.com/openjdk/valhalla/blob/1077e4f9f06336af30d95fc28cbab4d31c9f2a44/src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp#L3614-L3620
>> 
>> So, we save r0-r7 and r10-r17
>> 
>> # `CardTableBarrierSetAssembler::oop_store_at` in `cardTableBarrierSetAssembler_aarch64.cpp`
>> 
>> https://github.com/openjdk/valhalla/blob/1077e4f9f06336af30d95fc28cbab4d31c9f2a44/src/hotspot/cpu/aarch64/gc/shared/cardTableBarrierSetAssembler_aarch64.cpp#L116-L124
>> 
>> Digging the history looks like it still makes sense, it doesn't look like an accident. If we remove the if-branch, tests are totally on fire. Let's keep it.
>> 
>> # `CardTableBarrierSetAssembler::oop_store_at` in `cardTableBarrierSetAssembler_x86.cpp`
>> 
>> Same as before. But it's not even guarantee that `InlineTypePassFieldsAsArgs` is true. We can have such a backtrace:
>> 
>> CardTableBarrierSetAssembler::oop_store_at (cardTableBarrierSetAssembler_x86.cpp:184)
>> CardTableBarrierSetAssembler::store_at (cardTableBarrierSetAssembler_x86.cpp:90)
>> MacroAssembler::store_heap_oop (macroAssembler_x86.cpp:5515)
>> do_oop_store (templateTable_x86.cpp:148)
>> (called, for instance, from TemplateTable::putfield_or_static_helper (templateTable_x86.cpp:2964))
>> 
>> where the last give `r8` for `tmp3`. It is not quite clear to me why we don't have a problem in mainline, because it looks like corrupting address base register is a bad idea given that we use it after.
>> 
>> # `MacroAssembler::unpack_inline_helper` in `macroAssembler_aarch64.cpp`
>> 
>> ## First part
>> https://github.com/openjdk/valhalla/blob/1077e4f9f06336af30d95fc28cbab4d31c9f2a44/src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp#L7163-L7166
>> 
>> Yes, these registers are saved, as we saw above! I've added some asserts to mak...
>
> Marc Chevalier has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Pick the right comment again

Looks good.

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Marked as reviewed by thartmann (Committer).

PR Review: https://git.openjdk.org/valhalla/pull/1824#pullrequestreview-3626027393