RFR: 8365604: Null pointer dereference in src/hotspot/share/adlc/output_h.cpp ArchDesc::declareClasses() [v2]

[Artem Semenov]

On Wed, 20 Aug 2025 12:20:51 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Artem Semenov has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Update src/hotspot/share/c1/c1_LinearScan.cpp
>>    
>>    Co-authored-by: David Holmes <62092539+dholmes-ora at users.noreply.github.com>
>>  - Update src/hotspot/share/adlc/output_h.cpp
>>    
>>    Co-authored-by: David Holmes <62092539+dholmes-ora at users.noreply.github.com>
>
> src/hotspot/share/nmt/mallocSiteTable.cpp line 172:
> 
>> 170:        index < pos_idx && head != nullptr;
>> 171:        index++, head = ((MallocSiteHashtableEntry*)head->next() == nullptr) ? head :
>> 172:       (MallocSiteHashtableEntry*)head->next()) {}
> 
> This doesn't look right to me. We check `head != nullptr` in the loop condition so we cannot reach the assignment if it is null.

A situation is possible where head becomes nullptr when head->next() returns nullptr on the last iteration. Then, after the loop finishes, assert(head != nullptr) will trigger (only in debug mode), and return head->data() will cause a program error

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PR Review Comment: https://git.openjdk.org/jdk/pull/26798#discussion_r2290418847