RFR: 8253795: Implementation of JEP 391: macOS/AArch64 Port [v2]

[Anton Kozlov]

On Mon, 25 Jan 2021 14:36:35 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Anton Kozlov has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Address feedback for signature generators
>>  - Enable -Wformat-nonliteral back
>
> src/hotspot/share/jfr/instrumentation/jfrJvmtiAgent.cpp line 87:
> 
>> 85:   JavaThread* jt = JavaThread::thread_from_jni_environment(jni_env);
>> 86:   DEBUG_ONLY(JfrJavaSupport::check_java_thread_in_native(jt));;
>> 87:   Thread::WXWriteFromExecSetter wx_write;
> 
> Is this on every transition to VM from Native?  Would it be better to add to ThreadInVMfromNative like the ResetNoHandleMark is?

I've tried to do something like this initially. The idea was to use Write in VM state and Exec in Java and Native states. However, for example, JIT runs in the Native state and needs Write access. So instead, W^X is managed on entry and exit from VM code, in macros like JRT_ENTRY. Unfortunately, not every JVM entry function is defined with an appropriate macro (at least for now), so I had to add explicit W^X state management along with the explicit java thread state, like here.

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PR: https://git.openjdk.java.net/jdk/pull/2200