tarantool / luajit / 30338820236

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] produces a warning about
signed integer overflow in the function carith_ptr(), when idx
equals INT_MIN in the expression idx = -idx. In practice,
negating INT_MIN 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.

The patch follows up the commit 78f4de4d7
("Avoid negation of signed integers in C that may hold INT*_MIN.").

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

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

Part of tarantool/tarantool#12880

Coverage Stats

5731 of 6058 branches covered (94.6%)

Branch coverage included in aggregate %.

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

24 existing lines in 4 files now uncovered.

21854 of 23555 relevant lines covered (92.78%)

3969953.34 hits per line