RFR: 8310239: Add missing cross modifying fence in nmethod entry barriers [v2]

Mon Oct 2 19:23:29 UTC 2023

On Wed, 27 Sep 2023 12:38:37 GMT, Andrew Haley <aph at openjdk.org> wrote:

> > > Do we need an ISB on AArch64-specifc code? There, the guard value is data, not an immediate field.
> 
> > > In other words, what instruction has just been patched that we need to make visible?
> 
> > 
> 
> > On AArch64 we only use synchronous cross-modifying code, we just hide the expensive in slow paths using a epoch trick that proves that most executions don't need a fence. So that should all be fine. Sometimes I wonder if we should use that trick on x86_64 as well.
> 
> 
> 
> I don't understand this reply. On AArch64 we don't patch code, we patch data. So why do we need to add a missing ISB to AArch64?

Generational ZGC patches code too.

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PR Comment: https://git.openjdk.org/jdk/pull/14543#issuecomment-1743618934