TIOCGWINSZ modifies its argument, so it needs to mutably borrow it.
Unfortunately, ioctl()'s signature is not able to enforce this, and
the write happens in the kernel, so I don't think anything like miri,
valgrind, UBSan, etc. would have been able to catch this.
The UB passing an immutable reference caused resulted, for me, in
get_win_size() returning (0, 0) since LLVM commit
9a09c737a052 ("[BasicAA] Make isNotCapturedBeforeOrAt() check for
calls more precise (#69931)").
I've had a look through the other ioctl() calls in Cloud Hypervisor,
and I don't think any others have the same problem.
Signed-off-by: Alyssa Ross <hi@alyssa.is>
e7c7a304e8