On Wed, 13 Mar 2024 13:53:46 GMT, Richard Reingruber <rr...@openjdk.org> wrote:
>> src/hotspot/share/jfr/instrumentation/jfrJvmtiAgent.cpp line 160: >> >>> 158: ResourceMark rm(THREAD); >>> 159: // WXWrite is needed before entering the vm below and in callee >>> methods. >>> 160: MACOS_AARCH64_ONLY(ThreadWXEnable __wx(WXWrite, THREAD)); >> >> I understand you placed this here to cover the transition inside >> `create_classes_array` and the immediate one at line 170, but doesn't this >> risk having the wrong WX state for code in between? > > I've asked this myself (after making the change). > Being in `WXWrite` mode would be wrong if the thread would execute > dynamically generated code. There's not too much happening outside the scope > of the `ThreadInVMfromNative` instances. I see jni calls > (`GetObjectArrayElement`, `ExceptionOccurred`) and a jvmti call > (`RetransformClasses`) but these are safe because the callees enter the vm > right away. We even avoid switching to `WXWrite` and back there. > So I thought it would be ok to coarsen the WXMode switching. > But maybe it's still better to avoid any risk especially since there's likely > no performance effect. Or could the `ThreadInVMfromNative tvmfn(THREAD);` in `check_exception_and_log` be move out to `JfrJvmtiAgent::retransform_classes`? And then only use one `ThreadInVMfromNative` in `JfrJvmtiAgent::retransform_classes` ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/18238#discussion_r1530831165
