# 11.6. Futhark

Morloc Manual > Language Support | https://morloc-project.github.io/docs/languages/futhark.html | prev: https://morloc-project.github.io/docs/languages/rust.md | next: https://morloc-project.github.io/docs/install/index.md

## 11.6.1. Futhark backends and GPU devices

Futhark kernels are the first structured consumer of build parameters. Two keys are recognized:

-   `backend` — the Futhark compilation backend: one of `c` (the default, sequential CPU), `multicore` (parallel CPU), `opencl`, `cuda`, `hip`, or `ispc`. The GPU backends (`opencl`, `cuda`, `hip`) are what make Futhark run on a GPU.
-   `device` — which device to run on, for a GPU backend, using Futhark’s device selector syntax (`#0`, `#1`, …​). It is only valid together with a GPU backend.

```bash
# build the Futhark kernels for CUDA and run on the second GPU
morloc make -X futhark:backend=cuda -X futhark:device=#1 -o nexus main.loc
```

A GPU build runs on the single selected device, and calls into the Futhark context are serialized. The required GPU runtime libraries (for example `-lcuda -lnvrtc` for CUDA) are linked automatically; if your toolchain lives in a non-standard location, add the paths with the C++ escape hatch, e.g. `-X cpp:flags=-L/usr/local/cuda/lib64`.