| Issue |
136592
|
| Summary |
UBSan: Incorrect generated `__ubsan_handle_type_mismatch_v1`?
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
zanmato1984
|
In apache/arrow we encountered a weird UBSan error (https://github.com/apache/arrow/pull/46124#issuecomment-2814416656) which seems to be a false alarm. A reduced case can be found [here](https://godbolt.org/z/GsYcn155q) .
To summarize, for function:
```
uint64_t read64(const uint64_t* src, size_t n) {
uint64_t result = 0;
std::memcpy(&result, src, n);
return result;
}
```
A misaligned `src` shouldn't be considered UB because it is merely passed into `std::memcpy` as `void *` which requires no alignment. However the generated code jumps to `__ubsan_handle_type_mismatch_v1` once misaligned regardless of how it is used afterwards.
As a comparison, changing the pointer type from `uint64_t *` to `uint8_t *` gets the correct codegen - no alignment checking:
```
uint64_t read8(const uint8_t* src, size_t n) {
uint64_t result = 0;
std::memcpy(&result, src, n);
return result;
}
```
The same behavior is observed on X86 as well, and as early as 18.1.0 (17.0.1 is fine) for both Arm and X86.
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