RFR: 8221554: aarch64 cross-modifying code [v3]

[Alan Hayward]

On Mon, 12 Oct 2020 14:49:01 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> Alan Hayward has updated the pull request with a new target base due to a merge or a rebase. The pull request now
>> contains three commits:
>>  - AArch64: Add cross modify fence verification
>>  - AArch64: Use cross_modify_fence instead of maybe_isb
>>  - Split cross_modify_fence
>
> src/hotspot/os_cpu/linux_aarch64/orderAccess_linux_aarch64.hpp line 35:
> 
>> 33: #define inlasm_isb()    asm volatile("isb" : : : "memory")
>> 34:
>> 35: // Implementation of class OrderAccess.
> 
> This #define of inlasm_isb() looks wrong. Surely it should be in the body of OrderAccess::cross_modify_fence_impl()
> given that it's not used anywhere else. All the extra indirection does is confuse the reader.

Agreed. It was designed to fit with my patch which did the same for the dmb's - but I've closed that patch. Will fix.

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PR: https://git.openjdk.java.net/jdk/pull/428