[jmm-dev] [concurrency-interest] Will the real memory read barrier please stand up?

Andrew Haley aph at redhat.com
Mon Nov 24 09:33:23 UTC 2014

On 24/11/14 00:09, Doug Lea wrote:
> On 11/20/2014 05:25 AM, Andrew Haley wrote:
>> On 20/11/14 10:12, Joe Bowbeer wrote:
>>> As far as I can tell, the cookbook hasn't been updated yet for ARMv8.
> Mainly out of conservatism given the history of revising ARM and POWER
> entries multiple times over the years, sometimes based on incomplete or
> wrong information. It seems worth waiting for multiple validations,
> including experience from the ARMv8 hotspot port. This is cruel to Andrew
> (sorry!) but still better than alternatives.
>>> looks like the following might be helpful in updating the recipes.
>>> http://www.cl.cam.ac.uk/~pes20/cpp/cpp0xmappings.html
>> Yes, it looks like the DMB LD is now stronger if, that page is right.
>> It'd be nice if someone could point me at the language in the
>> ARMv8 spec that this derives from.
> I'm hoping that someone from ARM answers this.

I have communicated with ARM and (although it is implied in the the
ARMv8 Architecture Reference Manual in a roundabout way) they have
raised a ticket for clarification in a future update.  They agree that
Load-Load|Load-Store is correct.

In the meantime, there is a table of memory barriers on Page 105 of
the ARMv8 Instruction Set Overview which states this explicitly.


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