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

Gerard Ziemski gziemski at openjdk.java.net
Thu Feb 4 22:22:48 UTC 2021


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 198:

> 196: 
> 197: NOINLINE frame os::current_frame() {
> 198:   intptr_t *fp = *(intptr_t **)__builtin_frame_address(0);

In the bsd_x86 counter part we initialize `fp` to `_get_previous_fp()` - do we need to implement it on aarch64 as well (and using address 0 is just a temp workaround) or is it doing the right thing here?

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


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