RFR: 8253795: Implementation of JEP 391: macOS/AArch64 Port [v10]

[Gerard Ziemski]

On Wed, 3 Feb 2021 20:01:15 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 six additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'origin/jdk/jdk-macos' into jdk-macos
>  - Add comments to WX transitions
>    
>    + minor change of placements
>  - Use macro conditionals instead of empty functions
>  - Add W^X to tests
>  - Do not require known W^X state
>  - Revert w^x in gtests

src/hotspot/os_cpu/bsd_aarch64/os_bsd_aarch64.cpp line 403:

> 401:   }
> 402: 
> 403:   return false; // Mute compiler

Is this comment needed?

src/hotspot/os_cpu/bsd_aarch64/os_bsd_aarch64.cpp line 420:

> 418: size_t os::Posix::_compiler_thread_min_stack_allowed = 72 * K;
> 419: size_t os::Posix::_java_thread_min_stack_allowed = 72 * K;
> 420: size_t os::Posix::_vm_internal_thread_min_stack_allowed = 72 * K;

Those are slightly larger than their x86_64 counter parts. Are they conservative/aggressive values? How did we arrive at those?

src/hotspot/os_cpu/bsd_aarch64/os_bsd_aarch64.cpp line 652:

> 650: 
> 651: void os::setup_fpu() {
> 652: }

Is there really nothing to do here, or does still need to be implemented? A clarification comment here would help/.

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