RFR: 8369393: NMT: poison the malloc header and footer under ASAN build [v2]

[Afshin Zafari]

On Wed, 3 Dec 2025 14:11:08 GMT, Paul Hübner <phubner at openjdk.org> wrote:

>> Afshin Zafari 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 eight additional commits since the last revision:
>> 
>>  - Merge remote-tracking branch 'origin/master' into asan_poison_malloc_hdr_ftr_v2
>>  - removed extra newlines.
>>  - fixes.
>>  - inlining
>>  - review comments applied.
>>  - revision
>>  - jtreg test excluded when ASAN is enabled.
>>  - 8369393: NMT: poison the malloc header and footer under ASAN build
>
> src/hotspot/share/nmt/mallocHeader.inline.hpp line 170:
> 
>> 168:   ASAN_UNPOISON_MEMORY_REGION(header->footer_address(), footer_size);
>> 169:   resolve_checked(memblock);
>> 170:   header->mark_block_as_dead();
> 
> Unrelated to this PR: is there a reason we `mark_block_as_dead()` but `revive()` as opposed to `mark_block_as_revived()`?

I prefer `mark_block_as_alive()` with no assertion on being already `dead`. `revive()` with assertion that it has to be `dead` already. Thoughts?

> src/hotspot/share/runtime/os.cpp line 724:
> 
>> 722:       void* const new_outer_ptr = permit_forbidden_function::realloc(header, new_outer_size);
>> 723:       bool realloc_succeeded = new_outer_ptr != nullptr;
>> 724:       success = realloc_succeeded;
> 
> Nit: `realloc_succeeded` is only used here. Got briefly confused why there were two successes while reviewing.
> Suggestion:
> 
>       success = new_outer_ptr != nullptr; // reallocation succeeded

Suggestion accepted.

> src/hotspot/share/runtime/os.cpp line 739:
> 
>> 737: #endif
>> 738: 
>> 739:         success = true;
> 
> Redundant assignment?

Good catch! removed.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/28503#discussion_r2585403118
PR Review Comment: https://git.openjdk.org/jdk/pull/28503#discussion_r2585406002
PR Review Comment: https://git.openjdk.org/jdk/pull/28503#discussion_r2585402949