RFR: 8369393: NMT: poison the canaries of malloc header under ASAN build [v20]

[Afshin Zafari]

On Mon, 10 Nov 2025 10:27:48 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> Afshin Zafari has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   order of includes corrected.
>
> src/hotspot/share/nmt/mallocHeader.hpp line 126:
> 
>> 124:   inline static OutTypeParam resolve_checked_impl(InTypeParam memblock);
>> 125: 
>> 126:   void asan_poison_self() {
> 
> Why this complex? Why not just poison/unpoison the whole header in one call? You could simplify quite a bit that way.

The only reason is to avoid unpoisoning when accessing other fields as MemTag or MST_Marker, and poisoning back when access is completed. Now MemTag and mst_marker fields are free to be accessed without unpoisoning first.
I can change the issue title and do the whole header poisoning, if it is preferred.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27685#discussion_r2510115250