RFR: 8360941: [ubsan] MemRegion::end() shows runtime error: applying non-zero offset 8388608 to null pointer [v3]

[Matthias Baesken]

On Fri, 11 Jul 2025 17:25:50 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> src/hotspot/share/memory/memRegion.hpp line 67:
>> 
>>> 65:   HeapWord* start() const { return _start; }
>>> 66:   // in the gtests we call end() with a _start == nullptr so adjust the addition to avoid ub
>>> 67:   HeapWord* end() const   { return reinterpret_cast<HeapWord*>(reinterpret_cast<uintptr_t>(_start) + (_word_size * sizeof(HeapWord))); }
>> 
>> I don't think this change should be made. Instead, fix the offending test.  The fake heap it creates starts
>> at null, but I think it could be anywhere, because nothing touches it.
>
> If it did (or does) need to be valid memory, then just allocate a chunk of
> native memory for this fake heap for the test. That might be the safer thing
> to do anyway, in case some future change leads to the fake region getting
> touched.

> I don't think this change should be made. Instead, fix the offending test. The fake heap it creates starts at null, but I think it could be anywhere, because nothing touches it.

Let's do it this way !

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PR Review Comment: https://git.openjdk.org/jdk/pull/26216#discussion_r2210636582