RFR: 8346971: [ubsan] psCardTable.cpp:131:24: runtime error: large index is out of bounds

[Thomas Schatzl]

On Mon, 13 Jan 2025 09:33:30 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Please review this change to PSStripeShadowCardTable to avoid several examples
>> of UB in it's internal calculations.  We avoid the UB by switching to the
>> integer domain (using uintptr_t) for all of the internal calculations, with
>> casts between pointers and uintptr_t as needed at the boundaries.
>> 
>> This applies not just to the various pointer adjustments, but also to pointer
>> comparisons. In particular, the prior range check assertions using pointer
>> comparisons could have been partially or even completely "optimized" away
>> based on the no-UB assumption.
>> 
>> Testing: mach5 tier1-5
>> local (linux-x64) tier1 with -XX:+UseParallelGC
>
> src/hotspot/share/gc/parallel/psCardTable.cpp line 129:
> 
>> 127:   // Avoid UB pointer operations by using integers internally.
>> 128: 
>> 129:   static_assert(sizeof(intptr_t) == sizeof(CardValue*), "simplifying assumption");
> 
> Why check `sizeof(intptr_t)` instead of `uintptr_t` here?

I mean, the change uses `uintptr_t` throughput, and probably the size of `intptr_t` and `uintptr_t` must be(?) the same, but why not check the actually used type?

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PR Review Comment: https://git.openjdk.org/jdk/pull/23032#discussion_r1912960879