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

[Coleen Phillimore]

On Sun, 24 Jan 2021 15:32:59 GMT, Anton Kozlov <akozlov at openjdk.org> wrote:

>> Please review the implementation of JEP 391: macOS/AArch64 Port.
>> 
>> It's heavily based on existing ports to linux/aarch64, macos/x86_64, and windows/aarch64. 
>> 
>> Major changes are in:
>> * src/hotspot/cpu/aarch64: support of the new calling convention (subtasks JDK-8253817, JDK-8253818)
>> * src/hotspot/os_cpu/bsd_aarch64: copy of os_cpu/linux_aarch64 with necessary adjustments (JDK-8253819)
>> * src/hotspot/share, test/hotspot/gtest: support of write-xor-execute (W^X), required on macOS/AArch64 platform. It's implemented with pthread_jit_write_protect_np provided by Apple. The W^X mode is local to a thread, so W^X mode change relates to the java thread state change (for java threads). In most cases, JVM executes in write-only mode, except when calling a generated stub like SafeFetch, which requires a temporary switch to execute-only mode. The same execute-only mode is enabled when a java thread executes in java or native states. This approach of managing W^X mode turned out to be simple and efficient enough.
>> * src/jdk.hotspot.agent: serviceability agent implementation (JDK-8254941)
>
> 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?

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