On Wed, 3 Feb 2021 20:01:15 GMT, Anton Kozlov <akoz...@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 297:

> 295:           stub = SharedRuntime::handle_unsafe_access(thread, next_pc);
> 296:         }
> 297:       } else if (sig == SIGILL && nativeInstruction_at(pc)->is_stop()) {

Can we add a comment here describing what this case means?

-------------

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

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