RFR: JDK-8294947: Use 64bit atomics in patch_verified_entry on x86_64

[Dean Long]

On Wed, 9 Nov 2022 12:41:59 GMT, Dmitry Samersoff <dsamersoff at openjdk.org> wrote:

> In the void NativeJump::patch_verified_entry() we atomically patch first 4 bytes, then atomically patch 5th byte, then atomically patch first 4 bytes again. But from CMC (cross-modified code) point of view it's better to patch atomically 8 bytes at once.
> 
> The patch was tested with hotspot jtreg tests in bare-metal and virtualized environments.

src/hotspot/cpu/x86/nativeInst_x86.cpp line 511:

> 509: // In JVMCI, the restriction is enforced by HotSpotFrameContext.enter(...)
> 510: //
> 511: void NativeJump::patch_verified_entry(address entry, address verified_entry, address dest) {

Should we assert that the appropriate lock is held here?

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PR: https://git.openjdk.org/jdk/pull/11059