RFR: 8365163: [ubsan] left-shift issue in globalDefinitions.hpp [v5]

[Dean Long]

On Tue, 26 Aug 2025 13:51:53 GMT, Afshin Zafari <azafari at openjdk.org> wrote:

>> There was a left-shift of negative value UB in `set_high` function where the high value sign bit is on and is left-shifted 32 bits to put it in high word of the destination address.
>> To address it, first the left 32 bits of the provided `high` arg is cleared and then left-shifted 32 bits. 
>> 
>> Tests:
>> mach5 tiers 1-5 {macosx-aarch64, linux-x64, windows-x64} x {debug, product}
>
> Afshin Zafari has updated the pull request incrementally with one additional commit since the last revision:
> 
>   CONST64 vs explicit casting.

BTW, gcc x64 generates slightly better code using a union (which it converts into shifts anyway), but then we have to deal with endianness.

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PR Comment: https://git.openjdk.org/jdk/pull/26809#issuecomment-3225420652