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Advanced Build Instructions

This file covers a few advanced scenarios that go beyond what the basic build guide provides.

Customizing the disk image

To add, modify or remove files of the disk image's file system, e.g. to change the default keyboard layout, you can create a shell script with the name sync-local.sh in the project root, with content like this:

#!/bin/sh

set -e

cat << 'EOF' > mnt/etc/Keyboard.ini
[Mapping]
Keymaps=de
EOF

# Add a file in anon's home dir
cp /somewhere/on/your/system/file.txt mnt/home/anon

This will configure your keymap to German (de) instead of US English. See Base/res/keymaps/ for a full list. Note that the keymap program itself will also modify the /etc/Keyboard.ini config file, but this way the change will persist across image rebuilds.

Ninja build targets

The Meta/serenity.sh script provides an abstraction over the build targets which are made available by CMake. The following build targets cannot be accessed through the script and have to be used directly by changing the current directory to Build/i686 and then running ninja <target>:

  • ninja limine-image: Builds a disk image (limine_disk_image) with Limine
  • ninja grub-image: Builds a disk image (grub_disk_image) with GRUB
  • ninja extlinux-image: Builds a disk image (extlinux_disk_image) with extlinux
  • ninja check-style: Runs the same linters the CI does to verify project style on changed files
  • ninja install-ports: Copies the entire ports tree into the installed rootfs for building ports in Serenity
  • ninja lint-shell-scripts: Checks style of shell scripts in the source tree with shellcheck
  • ninja all_generated: Builds all generated code. Useful for running analysis tools that can use compile_commands.json without a full system build
  • ninja configure-components: See the Component Configuration section below.

CMake build options

There are some optional features that can be enabled during compilation that are intended to help with specific types of development work or introduce experimental features. Currently, the following build options are available:

  • ENABLE_ADDRESS_SANITIZER and ENABLE_KERNEL_ADDRESS_SANITIZER: builds in runtime checks for memory corruption bugs (like buffer overflows and memory leaks) in Lagom test cases and the kernel, respectively.
  • ENABLE_KERNEL_UNDEFINED_SANITIZER: builds in runtime checks for detecting undefined behavior in the kernel.
  • ENABLE_KERNEL_COVERAGE_COLLECTION: enables the KCOV API and kernel coverage collection instrumentation. Only useful for coverage guided kernel fuzzing.
  • ENABLE_USERSPACE_COVERAGE_COLLECTION: enables coverage collection instrumentation for userspace. Currently only works with a Clang build.
  • ENABLE_MEMORY_SANITIZER: enables runtime checks for uninitialized memory accesses in Lagom test cases.
  • ENABLE_UNDEFINED_SANITIZER: builds in runtime checks for undefined behavior (like null pointer dereferences and signed integer overflows) in Lagom test cases.
  • ENABLE_COMPILER_EXPLORER_BUILD: Skip building non-library entities in Lagom (this only applies to Lagom).
  • ENABLE_FUZZERS: builds fuzzers for various parts of the system.
  • ENABLE_FUZZERS_LIBFUZZER: builds Clang libFuzzer-based fuzzers for various parts of the system.
  • ENABLE_FUZZERS_OSSFUZZ: builds OSS-Fuzz compatible fuzzers for various parts of the system.
  • ENABLE_EXTRA_KERNEL_DEBUG_SYMBOLS: sets -Og and -ggdb3 compile options for building the Kernel. Allows for easier debugging of Kernel code. By default, the Kernel is built with -O2 instead.
  • ENABLE_ALL_THE_DEBUG_MACROS: used for checking whether debug code compiles on CI. This should not be set normally, as it clutters the console output and makes the system run very slowly. Instead, enable only the needed debug macros, as described below.
  • ENABLE_ALL_DEBUG_FACILITIES: used for checking whether debug code compiles on CI. Enables both ENABLE_ALL_THE_DEBUG_MACROS and ENABLE_EXTRA_KERNEL_DEBUG_SYMBOLS.
  • ENABLE_COMPILETIME_FORMAT_CHECK: checks for the validity of std::format-style format string during compilation. Enabled by default.
  • ENABLE_PCI_IDS_DOWNLOAD: downloads the pci.ids database that contains information about PCI devices at build time, if not already present. Enabled by default.
  • BUILD_LAGOM: builds Lagom, which makes various SerenityOS libraries and programs available on the host system.
  • ENABLE_KERNEL_LTO: builds the kernel with link-time optimization.
  • ENABLE_MOLD_LINKER: builds the userland with the mold linker. mold can be built by running Toolchain/BuildMold.sh.
  • ENABLE_JAKT: builds the jakt compiler as a Lagom host tool and enables building applications and libraries that are written in the jakt language.
  • JAKT_SOURCE_DIR: jakt developer's local checkout of the jakt programming language for rapid testing. To use a local checkout, set to an absolute path when changing the CMake cache of Lagom. e.g. cmake -S Meta/Lagom -B Build/lagom -DENABLE_JAKT=ON -DJAKT_SOURCE_DIR=/home/me/jakt
  • INCLUDE_WASM_SPEC_TESTS: downloads and includes the WebAssembly spec testsuite tests. In order to use this option, you will need to install prettier and wabt. wabt version 1.0.23 or higher is required to pre-process the WebAssembly spec testsuite.
  • INCLUDE_FLAC_SPEC_TESTS: downloads and includes the xiph.org FLAC test suite.
  • SERENITY_TOOLCHAIN: Specifies whether to use the established GNU toolchain, or the experimental Clang-based toolchain for building SerenityOS. See the Clang-based toolchain section below.
  • SERENITY_ARCH: Specifies which architecture to build for. Currently supported options are i686 and x86_64. x86_64 requires a separate toolchain build from i686.
  • BUILD_<component>: builds the specified component, e.g. BUILD_HEARTS (note: must be all caps). Check the components.ini file in your build directory for a list of available components. Make sure to run ninja clean and rm -rf Build/i686/Root after disabling components. These options can be easily configured by using the ConfigureComponents utility. See the Component Configuration section below.
  • BUILD_EVERYTHING: builds all optional components, overrides other BUILD_<component> flags when enabled

Many parts of the SerenityOS codebase have debug functionality, mostly consisting of additional messages printed to the debug console. This is done via the <component_name>_DEBUG macros, which can be enabled individually at build time. They are listed in this file.

To toggle or change a build option, see the CMake Cache Manipulation section below.

CMake Cache Manipulation

CMake caches variables and options in the binary directory. This allows a developer to tailor variables that are set() within the persistent configuration cache.

There are three main ways to manipulate the cache:

  • cmake path/to/binary/dir -DVAR_NAME=Value
  • ccmake (TUI interface)
  • cmake-gui

Options can be set via the initial cmake invocation that creates the binary directory to set the initial cache for the binary directory. Once the binary directory exists, any of the three options above can be used to change the value of cache variables.

For example, boolean options such as ENABLE_<setting> or <component_name>_DEBUG can be enabled with the value ON and disabled with OFF:

# Reconfigure an existing binary directory with process debug enabled
$ cmake -B Build/i686 -DPROCESS_DEBUG=ON

For more information on how the CMake cache works, see the CMake guide for Running CMake. Additional context is available in the CMake documentation for variables and set().

SuperBuild configuration

Serenity uses host tools written in idiomatic Serenity C++ to generate code and data for the main target build. The "SuperBuild" pattern helps to separate the host build of core Serenity libraries from the target build of the entire operating system environment. The SuperBuild allows clear separation of the host and target builds in the project's CMakeLists and unifies the approach taken towards different compiler toolchains and architectures.

The recommended way to build and run the system, ./Meta/serenity.sh run, invokes the SuperBuild equivalently to the commands below:

$ cmake -GNinja -S Meta/CMake/Superbuild -B Build/superbuild-i686 -DSERENITY_ARCH=i686 -DSERENITY_TOOLCHAIN=GNU
$ cmake --build Build/superbuild-i686
$ ninja -C Build/i686 setup-and-run

The CMake configuration of the superbuild-<arch> directory configures two ExternalProjects. The first project is lagom, which is the host build of the project. For more information on Lagom, see the Lagom ReadMe. It is used to build all the code generators and other host tools needed for the main Serenity build. The second project is the main build, which compiles the system for the target architecture using the selected toolchain.

The superbuild-<arch> configuration also generates the CMake toolchain file for the selected compiler toolchain and architecture via the -DSERENITY_ARCH and -DSERENITY_TOOLCHAIN arguments to the SuperBuild configuration step. The Serenity project depends on the install step of the Lagom build, as it uses find_package to locate the host tools for use in the code generation custom commands.

The SuperBuild build steps are roughly equivalent to the following commands:

# Generate CMakeToolchain.txt
mkdir -p Build/i686
cp Toolchain/CMake/GNUToolchain.txt.in Build/i686/CMakeToolchain.txt
sed -i 's/@SERENITY_ARCH@/i686/g' Build/i686/CMakeToolchain.txt
sed -i 's/@SERENITY_SOURCE_DIR@/'"$PWD"'/g' Build/i686/CMakeToolchain.txt
sed -i 's/@SERENITY_BUILD_DIR@/'"$PWD"'\/Build\/i686/g' Build/i686/CMakeToolchain.txt

# Configure and install Lagom
cmake -GNinja -S Meta/Lagom -B Build/lagom -DCMAKE_INSTALL_PREFIX=${PWD}/Build/lagom-install
ninja -C Build/lagom install
# Configure and install Serenity, pointing it to Lagom's install prefix
cmake -GNinja -B Build/i686 -DCMAKE_PREFIX_PATH=${PWD}/Build/lagom-install -DSERENITY_ARCH=i686 -DCMAKE_TOOLCHAIN_FILE=${PWD}/Build/i686/CMakeToolchain.txt
ninja -C Build/i686 install

Directing future ninja or cmake --build invocations to the superbuild-<arch> directory ensures that any headers or cpp files shared between the host and target builds will be rebuilt, and the new host tools and libraries will be staged to the lagom-install directory. This is where the superbuild differs from manually entering the commands above, it establishes a dependency between the install stage of lagom and the configure/build stages of Serenity.

The main limitation of the SuperBuild is that any non-option CMake cache variables such as component configuration or debug flag settings must be done after a build has started. That is, the CMakeCache.txt for the Serenity and Lagom builds is not created until the SuperBuild build starts and reaches the proper stage for the build in question. For more information on the CMake cache see the CMake Cache Manipulation section above.

The debug flags might be manipulated after a build per the following commands:

# Initial build, generate binary directories for both child builds
$ cmake -GNinja -S Meta/CMake/Superbuild -B Build/superbuild-i686 -DSERENITY_ARCH=i686 -DSERENITY_TOOLCHAIN=GNU
$ cmake --build Build/superbuild-i686

# Turn on process debug and don't build the browser for the Serenity build
$ cmake -B Build/i686 -DPROCESS_DEBUG=ON -DBUILD_BROWSER=OFF
$ ninja -C Build/i686 install

# Build host tests in Lagom build
$ cmake -S Meta/Lagom -B Build/lagom -DBUILD_LAGOM=ON
$ ninja -C Build/lagom install

Component Configuration

For selecting which components of the system to build and install, a helper program, ConfigureComponents is available.

It requires whiptail as a dependency, which is available on most systems in the newt or libnewt package. To build and run it, run the following commands from the Build/i686 directory:

$ ninja configure-components

This will prompt you which build type you want to use and allows you to customize it by manually adding or removing certain components. It will then run a CMake command based on the selection as well as ninja clean and rm -rf Root to remove old build artifacts.

Tests

For information on running host and target tests, see Running Tests. The documentation there explains the difference between host tests run with Lagom and target tests run on SerenityOS. It also contains useful information for debugging CI test failures.

Running SerenityOS with VirtualBox and VMware

Outside of QEMU, Serenity will run on VirtualBox and VMware. If you're curious, see how to install Serenity on VirtualBox or install Serenity on VMware.

Running SerenityOS on bare metal

Bare curious users may even consider sourcing suitable hardware to install Serenity on a physical PC.

Filesystem performance on Windows

If you're using the native Windows QEMU binary, QEMU is not able to access the ext4 root partition of the WSL2 installation without going via the 9P network file share. The root of your WSL2 distro will begin at the network path \\wsl$\{distro-name}.

Alternatively, you may prefer to copy Build/_disk_image and Build/Kernel/Kernel to a native Windows partition (e.g. /mnt/c) before running ninja run, in which case SERENITY_DISK_IMAGE will be a regular Windows path (e.g. 'D:\serenity\_disk_image').

Clang-based toolchain

SerenityOS can also be built with the Clang compiler instead of GCC. This is useful for stopping us from relying on compiler-specific behavior, and the built-in static analyzer helps us catch more bugs. Code compiled with both of these toolchains works identically in most cases, with the limitation that ports can't be built with Clang yet.

To build the Clang-based toolchain, run BuildClang.sh from the Toolchain directory. The script defaults to building the tooling needed for 32-bit SerenityOS, but the ARCH=x86_64 environment variable can be set to build the 64-bit toolchain.

Warning: While the build script is running, your computer may slow down extremely or even lock up for short intervals. This generally happens if you have more CPU cores than free RAM in gigabytes. To fix this, limit the number of parallel compile tasks be setting the MAKEJOBS environment variable to a number less than your CPU core count.

Once the build script finishes, you can use it to compile SerenityOS. Either set the SERENITY_TOOLCHAIN build option to Clang as shown above, or pass Clang as the TOOLCHAIN option to Meta/serenity.sh, for example: Meta/serenity.sh run i686 Clang.