[clang] [lldb] [Clang] Introduce OverflowBehaviorType for fine-grained overflow control (PR #148914)

[Oliver Hunt via cfe-commits]

ojhunt wrote:


> These changes in semantics can introduce security vulnerabilities where previously none existed. Take the format string example in the RFC, which was called out as a result of this change in behavior, which is the reason I assumed it had be removed:

Sorry, I didn't include the most obvious security vulnerability:

```cpp
   uint16_t __wrap count = ...;
   malloc(sizeof(SomeType) * count);
```

The narrowing behavior truncates the allocation size.

Just to be clear though, the developer may not have explicitly state `__wrap` here: because of the way types are merged and propagated that `uint16_t __wrap` may have originally been a uint64_t, but every operation involving the `uint16_t __wrap` has resulted in the types being constantly narrowed. That would mean even if the code was

```cpp
   uint64_t count = ...;
   malloc(sizeof(SomeType) * count);
```

The RHS expression may have already been truncated - it might directly have the type `uint16_t __wrap` or that may have been lost earlier on, making it even harder to track down.



https://github.com/llvm/llvm-project/pull/148914