RFR: 8346923: MetaspaceShared base calculation may cause overflow in align_up

[Calvin Cheung]

On Tue, 21 Jan 2025 17:30:26 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> This fix adds overflow detection in `MetaspaceShared::compute_shared_base` before calling `align_up`. It is needed in order to work with the proposed changes for [JDK-8318127](https://bugs.openjdk.org/browse/JDK-8318127) which will add an `assert` to check for overflow.
>> 
>> Passed tiers 1 - 4 testing.
>
> Looks good to me.

Thanks @iklam and @matias9927 for the review.

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PR Comment: https://git.openjdk.org/jdk/pull/23168#issuecomment-2617050043