tarantool / luajit / 30092415860

93%

tarantool/master: 93%

Build Type

push

github

Committed by ligurio

Commit Message

FFI: Prevent sanitizer warning in carith_ptr().

Reported by Sergey Bronnikov.

(cherry picked from commit c3b379bf5)

The Undefined Behaviour Sanitizer [1] produce a warning about
signed integer overflow in the function carith_ptr(), when idx
equals INT_MIN in the expression idx = -idx. In practice,
on 32-bit platforms, negating -2147483648 wraps back to itself
instead of producing the correct positive value, leading to
incorrect pointer arithmetic in carith_ptr() for MM_sub (pointer
subtraction). The patch fixes that by converting idx to unsigned
(uintptr_t), computes two's complement negation via bitwise
negation + 1 (safe from overflow in unsigned arithmetic), and casts
back to ptrdiff_t. This avoids signed overflow entirely and
correctly negates even the INT_MIN edge case.

[1]: https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html

Sergey Bronnikov:
* added the description and the test for the problem

Part of tarantool/tarantool#12480

Coverage Stats

5734 of 6058 branches covered (94.65%)

Branch coverage included in aggregate %.

1 of 1 new or added line in 1 file covered. (100.0%)

12 existing lines in 2 files now uncovered.

21871 of 23555 relevant lines covered (92.85%)

3971505.22 hits per line