RFR: 8346714: [ASAN] compressedKlass.cpp reported applying non-zero offset to null pointer [v3]

[Coleen Phillimore]

On Fri, 20 Dec 2024 16:08:12 GMT, SendaoYan <syan at openjdk.org> wrote:

>> Hi all,
>> CompressedKlassPointers::sanity_check_after_initialization() src/hotspot/share/oops/compressedKlass.cpp:104:38 reported runtime error: applying non-zero offset 4294967296 to null pointer by clang17 UndefinedBehaviorSanitizer.
>> 
>> The _base initial as nullptr in function CompressedKlassPointers::initialize(address addr, size_t len) shows as below. In C/C++, offsetting a null pointer is undefined behavior. This PR do not change the original logic but eliminate the undefined behaviour in code, the risk is low.
>> 
>> ```c++
>>     address const end = addr + len;
>>     if (end <= (address)unscaled_max) {
>>       _base = nullptr;
>>       _shift = 0;
>
> SendaoYan has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Use uintptr_t instead intptr_t
>  - cast offset to intptr_t to avoid overflow

This looks better than the conditional on _addr. Thanks for fixing these errors.

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Marked as reviewed by coleenp (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/22848#pullrequestreview-2518204831