RFR: 8255233: InterpreterRuntime::at_unwind should be a JRT_LEAF

[Erik Österlund]

On Fri, 23 Oct 2020 09:45:11 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

> InterpreterRuntime::at_unwind is called at the very beginning of remove_activation(), to notify concurrent stack processing that a frame is about to be unwound. It is currently a JRT_ENTRY, because it needs a last_Java_frame to see what frame is about to get unwound.
> 
> However, there are special return paths used by JVMTI pop frame, that checks if the caller frame is deoptimized, then calls a special path that removes the top activation, assuming that does not enter the deopt handler. The new JRT_ENTRY makes that reasoning invalid.
> 
> Therefore, we need this to be a JRT_LEAF, that sets a last Java frame, to make everyone happy. This patch performs that change.
> 
> I have run tier 1-5 testing, and manually tested:
> 
> while true; do make test JTREG="RETAIN=all" TEST=open/test/hotspot/jtreg/vmTestbase/nsk/jvmti/ForceEarlyReturn/ForceEarlyReturn002 TEST_OPTS_JAVA_OPTIONS="-XX:+UseZGC -Xmx2g -XX:ZCollectionInterval=0.0001 -XX:ZFragmentationLimit=0.01 -XX:+VerifyOops -XX:+ZVerifyViews" ; done
> 
> Before the fix it crashes ~1/15 runs with a bad oop. After the fix, it doesn't crash. I have run it more times than my tmux buffer fits (for a day), and it does not fail any more with this fix.
> 
> Unfortunately, my testing on AArch64 has been stalled for a day, so I have sent out this PR without the testing of those bits being finished. I won't push until I get the results back, of course. But I am expecting that to be fine, as there is nothing special going on there and it compiles. Will post a comment when the complete results have arrived.

The delayed AArch64 test results are in: looking good as expected. However the github bot complained about x86 32 bit needing a cast, so hopefully fixed that now. I guess we will see what the bot has to say. Thank you bot for finding that.

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PR: https://git.openjdk.java.net/jdk/pull/828