zanmato1984 commented on code in PR #46124:
URL: https://github.com/apache/arrow/pull/46124#discussion_r2049948899
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cpp/src/arrow/compute/row/compare_internal.cc:
##########
@@ -276,7 +276,8 @@ void KeyCompare::CompareVarBinaryColumnToRowHelper(
int32_t tail_length = length - j * 8;
uint64_t tail_mask = ~0ULL >> (64 - 8 * tail_length);
uint64_t key_left = 0;
- std::memcpy(&key_left, key_left_ptr + j, tail_length);
+ const uint8_t* src_bytes = reinterpret_cast<const uint8_t*>(key_left_ptr
+ j);
Review Comment:
As explained in
https://github.com/apache/arrow/pull/46124#issuecomment-2814416656 , it could
be confusing to people why this casting is ever needed, given that it is
eventually passed down into `std::memcpy` as a `void *`. We can use a comment.
```suggestion
// NOTE: UBSAN may falsely report "misaligned load" in `std::memcpy`
on some
// platforms when using 64-bit pointers. Cast to an 8-bit pointer to
work around
// this.
const uint8_t* src_bytes = reinterpret_cast<const
uint8_t*>(key_left_ptr + j);
```
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