To call native functions, use [`[DllImport]`](https://docs.microsoft.com/en-us/dotnet/api/system.runtime.interopservices.dllimportattribute?view=net-6.0):
```c#
[DllImport("MyNativeLibrary")]
public static extern int Foo(int arg);
```
Burst also supports internal calls implemented inside Unity:
```c#
// In UnityEngine.Mathf
[MethodImpl(MethodImplOptions.InternalCall)]
public static extern int ClosestPowerOfTwo(int value);
```
`DllImport` is only supported for [native plug-ins](https://docs.unity3d.com/Manual/NativePlugins.html), not platform-dependent libraries like `kernel32.dll`.
For all `DllImport` and internal calls, you can only use the following types as parameter or return types:
|Pointers and references|`sometype*` : Pointer to any of the other types in this list<br/>`ref sometype` : Reference to any of the other types in this list
|Handle structs|`unsafe struct MyStruct { void* Ptr; }` : Struct containing a single pointer field<br/>`unsafe struct MyStruct { int Value; }` : Struct containing a single integer field
> [!NOTE]
>Passing structs by value isn't supported; you need to pass them through a pointer or reference. The only exception is that handle structs are supported. These are structs that contain a single field of pointer or integer type.
