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

[Ioi Lam]

On Fri, 17 Jan 2025 00:48:14 GMT, Calvin Cheung <ccheung 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.

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Marked as reviewed by iklam (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/23168#pullrequestreview-2565295893