RFR: 8366421: ModifiedUtf.utfLen may overflow for giant string [v2]

[Roger Riggs]

On Thu, 18 Sep 2025 12:49:50 GMT, Guanqiang Han <ghan at openjdk.org> wrote:

>> Please review this patch.
>> 
>> **Description:**
>> 
>> Currently, ModifiedUtf.utfLen returns a signed int. For very large strings, this may overflow and produce negative values, leading to incorrect behavior in code that relies on the UTF length. This patch changes the return type to long, which fully resolves the issue and allows safe handling of giant strings.
>> 
>> **Test:**
>> 
>> GHA
>
> Guanqiang Han has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - add regression test
>  - Merge remote-tracking branch 'upstream/master' into 8366421
>  - Change return type of utfLen to long to prevent overflow

test/jdk/jdk/internal/util/TestUtfLen.java line 54:

> 52:         if (total != expected) {
> 53:             throw new RuntimeException("Expected total=" + expected + " but got " + total);
> 54:         }

This misses the point of testing utfLen; it is always testing the same string testing only the inner path through the code.
The PR changes the callers of utfLen and they should be tested, not just the internal function.
The test really does need to create the large string and pass it to the APIs that have been changed.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27285#discussion_r2359593518