RFR: JDK-8300080: offset_of for GCC/Clang exhibits undefined behavior and is not always a compile-time constant

[Kim Barrett]

On Thu, 12 Jan 2023 20:36:31 GMT, Justin King <jcking at openjdk.org> wrote:

>> The implementation of `offset_of` for GCC/Clang only deals with types are aligned to 16 bytes or less, if they are more, such as `zCollectedHeap` the behavior is undefined. UBSan also suggests that `offset_of` is not always a compile time constant, as the stack trace came from the dynamic loader during library loading. This patch changes `offset_of` to use `offsetof` and disables the warning `invalid-offsetof` for the JVM.
>
> @aph FYI undoes `offset_of` change from JDK-8294902

Also @jcking , please always assign a subcompent for hotspot bugs in JBS.  I moved this one to the runtime subcomponent.

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PR: https://git.openjdk.org/jdk/pull/11978