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

[Andrew Haley]

On Thu, 4 Feb 2021 23:01:52 GMT, Gerard Ziemski <gziemski at openjdk.org> wrote:

>> 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 652:
> 
>> 650: 
>> 651: void os::setup_fpu() {
>> 652: }
> 
> Is there really nothing to do here, or does still need to be implemented? A clarification comment here would help/.

There is really nothing to do here.

> 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?

(0)``` looks right to me.

> src/hotspot/os_cpu/bsd_aarch64/os_bsd_aarch64.cpp line 291:
> 
>> 289:         bool is_unsafe_arraycopy = (thread->doing_unsafe_access() && UnsafeCopyMemory::contains_pc(pc));
>> 290:         if ((nm != NULL && nm->has_unsafe_access()) || is_unsafe_arraycopy) {
>> 291:           address next_pc = pc + NativeCall::instruction_size;
> 
> Replace
> 
> address next_pc = pc + NativeCall::instruction_size;
> 
> with
> 
> address next_pc = Assembler::locate_next_instruction(pc);
> 
> there is at least one other place that needs it.

Why is this change needed? AFAICS ```locate_next_instruction()``` is an x86 thing for variable-length instructions, and no other port uses it.

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