RFR: 8253795: Implementation of JEP 391: macOS/AArch64 Port

[Erik Joelsson]

On Fri, 22 Jan 2021 18:49:42 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)

Build changes in general look good.

make/autoconf/flags-cflags.m4 line 169:

> 167:       WARNINGS_ENABLE_ALL="-Wall -Wextra -Wformat=2 $WARNINGS_ENABLE_ADDITIONAL"
> 168: 
> 169:       DISABLED_WARNINGS="unknown-warning-option unused-parameter unused format-nonliteral"

Globally disabling a warning needs some motivation. Why is this needed? Does it really need to be applied everywhere or is there a specific binary or source file where this is triggered?

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