RFR: 8327990: [macosx-aarch64] JFR enters VM without WXWrite

[David Holmes]

On Tue, 12 Mar 2024 15:05:00 GMT, Richard Reingruber <rrich at openjdk.org> wrote:

> This pr changes  `JfrJvmtiAgent::retransform_classes()` and `jfr_set_enabled` to switch to `WXWrite` before transitioning to the vm.
> 
> Testing:
> make test TEST=jdk/jfr/event/runtime/TestClassLoadEvent.java TEST_VM_OPTS=-XX:+AssertWXAtThreadSync
> make test TEST=compiler/intrinsics/klass/CastNullCheckDroppingsTest.java TEST_VM_OPTS=-XX:+AssertWXAtThreadSync
> 
> More tests are pending.

src/hotspot/share/jfr/instrumentation/jfrJvmtiAgent.cpp line 160:

> 158:   ResourceMark rm(THREAD);
> 159:   // WXWrite is needed before entering the vm below and in callee methods.
> 160:   MACOS_AARCH64_ONLY(ThreadWXEnable __wx(WXWrite, THREAD));

I understand you placed this here to cover the transition inside `create_classes_array` and the immediate one at line 170, but doesn't this risk having the wrong WX state for code in between?

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PR Review Comment: https://git.openjdk.org/jdk/pull/18238#discussion_r1523127288