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

[Erik Österlund]

On Wed, 9 Aug 2023 00:15:00 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.

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PR Comment: https://git.openjdk.org/jdk/pull/14543#issuecomment-1695515725