RFR: AArch64: 8179954: AArch64: C1 and C2 volatile accesses are not sequentially consistent (original) (raw)

Aleksey Shipilev shade at redhat.com
Tue May 9 17:30:27 UTC 2017

On 05/09/2017 07:18 PM, Andrew Haley wrote:

In C2 we use LDAR/STLR to handle volatile accesses, but in C1 and the interpreter we use separate DMB instructions and relaxed loads. When used together, these do not form a sequentially-consistent memory ordering. For example, if stores use STLR and loads use LDR;DMB a simple Dekker idiom will fail.

This is extremely hard to test because the loads and stores have to be in separately-compiled methods, but it is incorrect, and likely to fail in very weakly-ordered implementations. Note: this is for JDK 9. http://cr.openjdk.java.net/~aph/8179954/

Makes sense to me.

-Aleksey

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