---
name: "kubsan"
section: "4"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["openbsd"]
url: "https://new.carta.tech/kubsan"
---

# kubsan(4)

kernel undefined behavior sanitizer

## NAME

**kubsan** – kernel undefined behavior sanitizer

## SYNOPSIS

**option** **KUBSAN**

## DESCRIPTION

**kubsan** detects undefined behavior at runtime inside the kernel. Detected undefined behavior is printed to the system console, including the offending line in the source code.

By default, **kubsan** is not enabled but instead requires the following line to be present in the kernel configuration:

```
option KUBSAN
```

The following undefined behavior is detected:

- Float cast overflow

  The conversion from a floating point to an integer cannot be represented by the destination type.

- Integer overflow

  The result of an arithmetic computation on two integer operands cannot be represented by the destination type.

- Negate overflow

  Negation of an integer cannot be represented by the destination type.

- Pointer overflow

  Pointer arithmetic overflow.

- Out of bounds

  Array indexing out of bounds, limited to cases where the size of the array can be statically determined.

- Shift out of bounds

  Undefined logical shift caused by:

  - The shift amount being negative.

  - The shift operand being negative.

  - The shift amount exceeds the number of bits as given by the shift operand type.

  - The result of the shift computation cannot be represented by the destination type.

- Non-null argument

  Passing NULL as the value for a function argument annotated with \_\_nonnull\_\_.

- Invalid builtin

  Passing zero to a compiler builtin where not allowed.

- Invalid load

  Loading a value that cannot be represented by the destination type.

- Type mismatch

  Mismatch between pointer and value type caused by:

  - A pointer which does not fulfill the alignment requirements of the value type.

  - A pointer to an address which lacks sufficient space to store the value type.

- Unreachable

  Execution reached passed a function annotated with \_\_dead.

## SEE ALSO

[options(4)](/options/4.md)

## HISTORY

The **kubsan** implementation is derived from NetBSD and first appeared in OpenBSD 6.5.

## AUTHORS

The **kubsan** implementation was written by Anton Lindqvist ⟨*anton@openbsd.org*⟩.

## CAVEATS

The **kubsan** implementation is limited to architectures using [clang(1)](/clang/1.md) as their default compiler.