Building and testing core locally

Because core is agnostic to Fuchsia, you can build and run using cargo, which can save a bit of development time. Follow the steps below to get a working local set up:

  • Navigate to directory //src/connectivity/network/netstack3/core.
  • If you haven't already, build netstack3 with fx build netstack3-core.
  • Run fx gen-cargo .:netstack3-core. That will create a new Cargo.toml file in that directory (which you can also use to import into your IDE if you use one!).

Note: the cargo generation is only a symbolic link to the fuchsia build output directory. You should only need to run this once. You must have an fx set line that includes netstack3 for the cargo file to be generated.

  • Add the following lines to your ~/.cargo/config file (or create it if you don't have one),
  • making sure to replace the absolute path to your fuchsia directory and the target match to your local development setup if different than x86_64-unknown-linux-gnu:
rustflags = ["-L", "absolute_path_to_fuchsia_directory/out/default/host_x64/obj/third_party/boringssl"]
  • Run cargo check from the core directory to check that everything is correct.


  • If you can't run cargo correctly after running jiri update, clean up all Cargo.lock files in //src and //garnet and try again.