RFR: 8221554: aarch64 cross-modifying code [v6]

[Andrew Haley]

On Fri, 23 Oct 2020 10:10:09 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 six commits:
>> 
>>  - Merge master
>>    
>>    Change-Id: I97df4e7686699478f0f89451ec0a3537d38cfd6d
>>  - Merge master
>>    
>>    Change-Id: I5e1715fdb11305191fe7bf86cbfb7a6da446b3dc
>>  - Remove inlasm_isb define
>>    
>>    Change-Id: I2d0ef8a78292dac875f3f65d2253981cdb7a497a
>>  - AArch64: Add cross modify fence verification
>>  - AArch64: Use cross_modify_fence instead of maybe_isb
>>  - Split cross_modify_fence
>
> src/hotspot/cpu/aarch64/templateInterpreterGenerator_aarch64.cpp line 1413:
> 
>> 1411:     __ blr(rscratch2);
>> 1412:     // An instruction sync is required here after the call into the VM. However,
>> 1413:     // that will have been caught in the VM by a cross_modify_fence call.
> 
> I think this wording is confusing; I had to read it several times. 
> 
> Would not something like
> '''
>     // When we return from the VM, the instruction stream may have
>     // been modified. Previously we emitted an ISB at this point, but
>     // it's now unnecessary because the VM itself calls cross_modify_fence()
> '''
> 
> be better?

This is still pending.

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