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

[Anton Kozlov]

On Tue, 26 Jan 2021 12:01:30 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> I assume a WXVerifier class that tracks W^X mode in debug mode and does nothing in release mode. I've considered to do this, it's relates to small inefficiencies, while this patch brings zero overhead (in release) for a platform that does not need W^X. 
>> * We don't need thread instance in release to call `os::current_thread_enable_wx`. Having WXVerifier a part of the Thread will require calling `Thread::current()` first and we could only hope for compiler to optimize this out, not sure if it will happen at all. In some contexts the Thread instance is available, in some it's not. 
>> * An instance of the empty class (as WXVerifier will be in the release) will occupy non-zero space in the Thread instance.
>> 
>> If such costs are negligible, I can do as suggested.
>
> I really just want the minimal number of lines of code and hooks in thread.hpp.  You can still access it through the thread, just like these lines currently.  Look at HandshakeState as an example.

Please take a look at the recent changes.

Changes in thread.hpp were reduced:
https://github.com/openjdk/jdk/pull/2200/files#diff-abdc409967d04172ecc20e3747aa55a79e755584d570b57c4d58902a9813d188

thread.inline.hpp provides definitions of accessors (non-trivial):
https://github.com/openjdk/jdk/pull/2200/files#diff-3a29f7f952bf2bd936f49e97cb3b86a7324851133e879c142dec724455310b50

And new threadWXSetters.hpp defines RAII context setter:
https://github.com/openjdk/jdk/pull/2200/files#diff-6424782ec43941031282f079e89adaa76d341ce340a3b78b0e9657358ec16278

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