[OpenJDK 2D-Dev] RFR: 8253795: Implementation of JEP 391: macOS/AArch64 Port [v23]

[David Holmes]

On Tue, 2 Mar 2021 21:19:18 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 five additional commits since the last revision:
> 
>  - Fix after JDK-8259539, partially revert preconditions
>  - JDK-8260471: bsd_aarch64 part
>  - JDK-8259539: bsd_aarch64 part
>  - JDK-8257828: bsd_aarch64 part
>  - Cleanup os_bsd_aarch64 signal handling

src/hotspot/os_cpu/bsd_aarch64/os_bsd_aarch64.cpp line 207:

> 205:   // Enable WXWrite: this function is called by the signal handler at arbitrary
> 206:   // point of execution.
> 207:   ThreadWXEnable wx(WXWrite, thread);

Note that `thread` can be NULL here if the signal handler is running in a non-attached thread.

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