RFR: 8366062: [ubsan] add non-zero offset to nullptr in cds/archiveBuilder.cpp [v3]

[David Holmes]

On Mon, 8 Sep 2025 08:44:47 GMT, Afshin Zafari <azafari at openjdk.org> wrote:

>> It is acceptable that the `SharedBaseAddress` option gets `0` at command line. The corresponding pointer arithmetic with `0` (`nullptr`) in archiveBuilder is UB.
>> Specific casts are used to avoid UBSAN error.
>> 
>> Tests:
>> linux-x64-debug: tier1 passed
>
> Afshin Zafari has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:
> 
>  - Merge remote-tracking branch 'origin/master' into _8366062_ubsan_nullptr_plus_nz_offset
>  - comments improved
>  - 8366062: [ubsan] add non-zero offset to nullptr in cds/archiveBuilder.cpp

That seems fine to me. Thanks

src/hotspot/share/cds/archiveBuilder.cpp line 1113:

> 1111:     address bottom = _builder->buffer_bottom();
> 1112:     address top = _builder->buffer_top();
> 1113:     // It is acceptable that new_bottom/new_top becomes zero.

Suggestion:

    // It is acceptable that new_bottom/new_top may be zero.

-------------

Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26983#pullrequestreview-3199759902
PR Review Comment: https://git.openjdk.org/jdk/pull/26983#discussion_r2332272876