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

[Andrew Haley]

On Mon, 28 Aug 2023 11:19:29 GMT, Erik Österlund <eosterlund 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?

-------------

PR Comment: https://git.openjdk.org/jdk/pull/14543#issuecomment-1737316137