RFR: 8346916: [REDO] align_up has potential overflow

[Dean Long]

On Thu, 20 Feb 2025 10:48:26 GMT, Casper Norrbin <cnorrbin at openjdk.org> wrote:

> Hi everyone,
> 
> The `align_up` function can potentially overflow, resulting in undefined behavior. Most use cases rely on the assumption that aligned_result >= original. To address this, I've added an assertion to verify this condition.
> 
> The original PR (#20808) missed cases where overflow checks already existed, so I've now went through usages of `align_up` and found the places with explicit checks. Most notably, #23168 added `align_up_or_null` to metaspace, but this function is also useful elsewhere. Given this, I relocated it to `align.hpp`, alongside the rest of the alignment functions.
> 
> Additionally, I've created `align_up_or_min`, which behaves similarly to the original align_up but handles overflows predictably across all integer types. This new function is used in the locations where overflow checks already exist, providing a safer alternative.

I don't see where we check the return value of align_up_or_min for the changes in src/hotspot/share/gc/shared/gcArguments.cpp.  If tests fail because of align_up, maybe the test should be fixed?

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PR Comment: https://git.openjdk.org/jdk/pull/23711#issuecomment-2675530338