RFR: 8331201: UBSAN enabled build reports on Linux x86_64 runtime error: shift exponent 65 is too large for 64-bit type 'long unsigned int' [v2]

[Dean Long]

On Thu, 19 Dec 2024 08:46:57 GMT, Afshin Zafari <azafari at openjdk.org> wrote:

>> The issue existed in making Fingerprints of method names. Each parameter in the methods' arguments is decoded as a 4-bits value. The 64-bits `fingertprint_t` can hold up to 14 parameters plus return type and static bit. To make the Fingerprint, the signature is iterated one parameter at a time and the corresponding code is accumulated after shifting the bits up.
>> Some compilers do not mask the shift value to the base size and UBSAN catches the case. 
>> In this PR, the number of parameters (`_param_count`) is used and compared with the max (14) to do the shift operation safely. The pre-existing `_param_size` is not reflecting the number of parameters, since it is incremented by 2 for `T_DOUBLE` and `T_LONG` types.
>
> Afshin Zafari has updated the pull request incrementally with one additional commit since the last revision:
> 
>   removed extra blank lines

src/hotspot/share/runtime/signature.hpp line 348:

> 346:       _accumulator |= ((fingerprint_t)type << _shift_count);
> 347:     }
> 348:     _param_count++;

Let's not introduce another field here.  We already have _shift_count that we can use to detect overflow.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22807#discussion_r1904685939