RFR: 8361487: [ubsan] test_committed_virtualmemory.cpp check_covered_pages shows overflow [v4]

[Paul Hübner]

On Thu, 13 Nov 2025 15:31:52 GMT, Afshin Zafari <azafari at openjdk.org> wrote:

>> In the test,  page-numbers to be checked are passed to a checker function in which they will be changed to `-1` if they are as expected.
>> Use of these `-1` values for page-numbers in consequent checks result in overflow in pointer arithmetic of `base + (-1) * page_size` which is certainly less than `base`.
>> 
>> The fix is to skip cases where page-number under checking is `-1`.
>> Tested under UBSAN build.
>
> Afshin Zafari has updated the pull request incrementally with one additional commit since the last revision:
> 
>   style and not constexpr

test/hotspot/gtest/runtime/test_committed_virtualmemory.cpp line 97:

> 95:         continue;
> 96:       }
> 97:       address page_addr = base + page_num[index] * page_sz;

What if we `assert(page_num[index] >= 0)` at this point if we know that negative numbers may cause overflows?

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PR Review Comment: https://git.openjdk.org/jdk/pull/28151#discussion_r2526444037