RFR: 8351334: [ubsan] memoryReserver.cpp:552:60: runtime error: applying non-zero offset 1073741824 to null pointer [v11]

[Afshin Zafari]

On Mon, 17 Nov 2025 01:18:11 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Afshin Zafari has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   fix arguments.cpp for HeapMinBaseAddress type.
>
> src/hotspot/share/memory/memoryReserver.cpp line 586:
> 
>> 584:                                           lowest_start, highest_start);
>> 585:       reserved = try_reserve_range((char*)highest_start, (char*)lowest_start, attach_point_alignment,
>> 586:                                    (char*)aligned_heap_base_min_address, (char*)UnscaledOopHeapMax, size, alignment, page_size);
> 
> Not obvious to me this actually improves anything - what is it fixing?

First, the pointer arithmetics are done on `uintptr_t` types to avoid UB.
Second, it is checked that `lowest` and `highest` are still valid after becoming larger or smaller, respectively.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26955#discussion_r2542076686