RFR: 8258032: Reconsider LEAF entry restrictions [v2]

[Ron Pressler]

On Tue, 5 Jan 2021 14:48:13 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> This change allows JRT_LEAF functions to create Handles because it doesn't need them but some code inside the VM needs Handles.  There's a NoSafepointVerifier in JRT_LEAF functions.
>> The JNI_LEAF and JVM_LEAF functions have NoHandleMark (so you can't create handles) but the transition ThreadInVMfromNative will reenable the HandleMarks, so that all this code doesn't have to do it itself.
>> Tested with tier1-6.
>
> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix copyrights.

Marked as reviewed by rpressler (Author).

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PR: https://git.openjdk.java.net/jdk/pull/1846