Developer Guide

Generating CHAI host-config files

This mechanism will generate a cmake configuration file that reproduces the configuration Spack <> would have generated in the same context. It will contain all the information necessary to build CHAI with the described toolchain.

In particular, the host config file will setup: * flags corresponding with the target required (Release, Debug). * compilers path, and other toolkits (cuda if required), etc. * paths to installed dependencies.

This provides an easy way to build CHAI based on Spack <> itself driven by Uberenv.

Uberenv role

Uberenv helps by doing the following:

  • Pulls a blessed version of Spack locally
  • If you are on a known operating system (like TOSS3), we have defined compilers and system packages so you don’t have to rebuild the world (CMake typically in CHAI).
  • Overrides CHAI Spack packages with the local one if it exists. (see scripts/uberenv/packages).
  • Covers both dependencies and project build in one command.

Uberenv will create a directory uberenv_libs containing a Spack instance with the required CHAI dependencies installed. It then generates a host-config file (<config_dependent_name>.cmake) at the root of CHAI repository.

Using Uberenv to generate the host-config file

$ python scripts/uberenv/


On LC machines, it is good practice to do the build step in parallel on a compute node. Here is an example command: srun -ppdebug -N1 --exclusive python scripts/uberenv/

Unless otherwise specified Spack will default to a compiler. It is recommended to specify which compiler to use: add the compiler spec to the --spec Uberenv command line option.

On blessed systems, compiler specs can be found in the Spack compiler files in our repository: scripts/uberenv/spack_configs/<System type>/compilers.yaml.

Some examples uberenv options:

  • --spec=%clang@4.0.0
  • --spec=%clang@4.0.0+cuda
  • --prefix=<Path to uberenv build directory (defaults to ./uberenv_libs)>

It is also possible to use the CI script outside of CI:

$ SPEC="%clang@9.0.0 +cuda" scripts/gitlab/ --deps-only

Building dependencies can take a long time. If you already have a Spack instance you would like to reuse (in supplement of the local one managed by Uberenv), you can do so changing the uberenv command as follow:

$ python scripts/uberenv/ --upstream=<path_to_my_spack>/opt/spack

Using host-config files to build CHAI

When a host-config file exists for the desired machine and toolchain, it can easily be used in the CMake build process:

$ mkdir build && cd build
$ cmake -C  <path_to>/lassen-blueos_3_ppc64le_ib_p9-clang@9.0.0.cmake ..
$ cmake --build -j .
$ ctest --output-on-failure -T test

It is also possible to use the CI script outside of CI:

$ HOST_CONFIG=<path_to>/<host-config>.cmake scripts/gitlab/

Testing new dependencies versions

CHAI depends on Umpire, and optionally RAJA. Testing with newer versions of both is made straightforward with Uberenv and Spack:

  • $ python scripts/uberenv/ --spec=%clang@9.0.0 ^umpire@develop
  • $ python scripts/uberenv/ --spec=%clang@9.0.0+raja ^raja@develop

Those commands will install respectively umpire@develop and raja@develop locally, and generate host-config files with the corresponding paths.

Again, the CI script can be used directly to install, build and test in one command:

$ SPEC="%clang@9.0.0 ^umpire@develop" scripts/gitlab/