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

[David Holmes]

On Wed, 19 Nov 2025 13:48:41 GMT, Afshin Zafari <azafari at openjdk.org> wrote:

>> src/hotspot/share/memory/memoryReserver.cpp line 590:
>> 
>>> 588: 
>>> 589:     // zerobased: Attempt to allocate in the lower 32G.
>>> 590:     size_t zerobased_max = OopEncodingHeapMax;
>> 
>> Again not obvious what this improves. We obviously have very inconsistent use of types here in that we loosely use `char*`, `uint64_t` and `size_t` to all mean a 64-bit unsigned value, ansd no matter what types we use in the declarations we have to cast something somewhere.
>
> According to reviewers' suggestions, the pointers used in arithmeitc are typed as numeric like `size_t` or `uintptr_t`. And only when they are going to be passed as pointers to other functions, they will be cast to the desired pointers.

Okay but why `size_t` in places and `uintptr_t` in others? In this case `zerobased_max` seems an address not a size - similar to `highest_start` and `lowest_start` in the other part of the change. But then `OopEncodingHeapMax` is `uint64_t` so why not use that?

I'm just not seeing the rules that are being applied here.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/26955#discussion_r2544365753