2.6. Project Structure

The Hafnium repository contains Hafnium source code, along with testing code related to integration tests, and unit tests. To aid with the integration tests, the repository also contains a small client library for partitions and prebuilt binaries of tools needed for the build and running the tests. The build system is supported by gn.

Each platform has a single associated architecture.

The source tree is organised as follows:

├── build
├── docs
├── driver
│   └── linux
├── inc
│   ├── hf
│   │   ├── arch
│   │   └── plat
│   ├── system
│   └── vmapi
│       └── hf
├── kokoro
├── prebuilts
├── project
├── src
│   ├── arch
├── test
│   ├── arch
│   ├── hftest
│   ├── inc
│   ├── linux
│   └── vmapi
├── third_party
├── tools
├── vmlib
└── out

build: Common GN configuration, build scripts, and linker script.
docs: Documentation.
driver/linux: Linux kernel driver for Hafnium as the hypervisor, in the primary VM (More details see legacy Hypervisor documentation).
inc: Header files.
- hf: internal to Hafnium.
  arch: Architecture-dependent modules, which have a common interface but separate implementations per architecture. This includes details of CPU initialisation, exception handling, timers, page table management, and other system registers.
  
  plat: Platform-dependent modules, which have a common interface but separate implementations per platform. This includes details of the boot flow, and a UART driver for the debug log console.
- system: which are included by the stdatomic.h which we use from Android Clang but not really needed, so we use dummy empty versions.
- vmapi/hf: for the interface exposed to partitions.
kokoro: Scripts and configuration for continuous integration and presubmit checks.
prebuilts: Prebuilt binaries needed for building Hafnium or running tests.
project: Configuration and extra code for each project. A project is a set of one or more platforms (see above) that are built together. Hafnium comes with the reference project for running it on some common emulators and development boards. To port Hafnium to a new board, you can create a new project under this directory with the platform or platforms you want to add, without affecting the core Hafnium code.
src: Source code for Hafnium itself in C and assembly, and unit tests in C++.
- arch: Implementation of architecture-dependent modules.
test: Integration tests
- arch: Tests for components of Hafnium that need to be run on a real architecture.
- hftest: A simple test framework that supports running tests standalone on bare metal, in partitions under Hafnium. Also as user-space binaries under Linux, but these are not yet integrated with system where Hafnium is the SPMC.
- linux: Tests which are run in a Linux partition under Hafnium as normal world hypervisor.
- vmapi: Tests which are run in minimal test partitions under Hafnium.
  arch: Tests which are rely on specific architectural details such as the GIC version.
  
  primary_only: Tests which run only a single (primary) partition.
  
  primary_with_secondaries: Test which run with a primary partition and one or more secondary partitions to test how they interact.
third_party: Third party code needed for building Hafnium.
vmlib: A small client library for partitions running under Hafnium.
out: Output directory for the build artifacts.