build/docs/build.md

The Pygos Build System

The Pygos system can be built by running the mk.sh shell script with the desired product configuration as argument.

The shell script can be run from anywhere on the file system. All configuration files and scripts are accessed relative to the source location of the script and all generated files are accessed relative to the current working directory.

Actually it is even strongly encouraged to run the build system from outside the git tree to have the generated files cleanly separated from the build system.

A second script named check_update.sh is provided to automatically query all upstream package sources to check if newer versions are available.

The mk.sh creates a download and a src directory. In the former it stores downloaded package tar balls, in the later it extracts the tar balls and applies patches.

For all other files and directories, a sub directory named after the product configuration is created. Throughout the build system, this directory is referred to as build root.

Inside the build root a deploy directory is created. Build output for each package is deployed to a sub directory named after the package.

The cross toolchain is stored in <build root>/toolchain.

Outputs and diagnostic messages of the build processes are stored in <build root>/toolchain/log/<package>-<stage>.log.

Package Build Scripts

The directory pkg contains a sub directory for each package. Each package directory is expected to contain a shell script named build.

The build script is expected to set the following variables:

• VERSION containing a package version number.
• URL containig a URL from which to download a source tar ball.
• TARBALL containing the name of the source tar ball. This is appended to the URL to download the package.
• SHA256SUM containing the SHA-256 check sum of the source tar ball.
• SRCDIR containing the name of the source directory unpacked from the tar ball.
• DEPENDS containing a space separated list of packages that the package in question depends on. Those packages are built first. Their headers and libraries are copied into the cross toolchain before building the current package and removed after building it.

Using the specified variables, the build system automatically downloads, verifies and unpacks the source tar balls (unless that has already been done) and determines the order in which to build the packages.

The build script is also expected to implement the following functions:

• prepare is run after unpacking the source tar ball. The current working directory is set to the source directory. The path to the package directory is passed as first argument, so the function can easily access patch files stored in the package directory. All output and error messages from the script are stored in <packagename>-prepare.log.
• build is run to compile the package. The current working directory is a temporary directory inside the build root directory. The source directory is passed as first argument. The second argument is a path to the deploy directory where generated files are installed. All standard output and error messages from the script are piped to <packagename>-build.log.
• deploy is run after compilation to install the build output to the deploy directory. Arguments and working directory are the same as for build. All output and error messages from the script are piped to <packagename>-deploy.log. The deploy function is also expected to generate a file named rootfs_files.txt that contains a listing of all files in the deploy directory that should be included in the root filesystem and what permissions should be set on them. Once the function returns, the mk.sh script strips everything installed to bin and lib, so the implementation doesn't have to do that. In fact install-strip Makefile targets should not be used since many implementations are broken for cross compilation. Further common steps are executed for packages that produce libtool archives and pkg-config files.
• check_update is only used by the check_update.sh script. It is supposed to find out if the package has a newer version available, and if so, echo it to stdout.

Environment Variables

The mk.sh sets a number of shell variables that package scripts can use.

The following variables describe the target system and the build environment:

• BOARD contains the target board specified on the command line
• PRODUCT contains the product name specified on the command line
• TARGET specifies the host triplet of the target board
• OS_NAME is statically set to Pygos
• OS_RELEASE holds a version string generated using git-describe
• NUMJOBS contains the number of processors available for parallel builds
• HOSTTUPLE contains the host triplet of the machine that the build system is running on for compiling toolchain packages.
• CMAKETCFILE contains the absolute path to a CMake toolchain file that can be used for compiling CMake based packages with the cross toolchain.

And a number of variables containing special directories:

• BUILDROOT contains the absolute path to the build root directory, i.e. the output directory within the working directory of the mk.sh script.
• SCRIPTDIR contains the absolute path to the script directory, i.e. the git tree with the build system in it.
• TCDIR contains the absolute path to the cross toolchain directory.
• PKGBUILDDIR contains the absolute path of the temporary directory in which the package is being built.
• PKGSRCDIR contains the root directory of all unpacked package tar balls
• PKGDEPLOYDIR contains the root directory of all package deploy directories
• PKGLOGDIR holds the absolute path of the directory containing all log files
• PKGDOWNLOADDIR holds the absolute path of the directory containing all package tar balls

The cross toolchain directory containing the executable prefixed with $TARGET- is also prepended to PATH.

Utility Functions

Some utility functions are provided for common package build tasks:

• apply_patches can be used inside the prepare function to automatically apply patches stored in the package directory to the source tree.
• strip_files takes a list of files as argument and runs the cross toolchain strip program on those that are valid ELF binaries. If a directory is encountered, the function recursively processes the sub directory. Usually you don't need to use this. The mk.sh script uses this function to after the deploy step to process the bin and lib directories.
• verson_find_greatest can be used in check_update to find the largest version number from a list. The list of version numbers is read from stdin. Version numbers can have up to four dot separated numbers or characters.
• run_configure can be used to run autoconf generated configure scripts with all the required options set for cross compilation. Extra options can be to the options passed to configure.

Configuration Files

The configuration for the build system is organized in layers, stored in the layer directory in the git tree.

The configuration on how to build an image for a specific target is a file in the product sub directory that specifies, what configuration layers to use and how to stack them on top of each other. Layers that are further down in the file override the ones before them.

From the layer configuartion, the build system itself merges (in layer precedence order) and processes the following configuration files:

• ROOTFS contains a list of packages that should be built and installed to the root filesystem.
• TOOLCHAIN contains shell variables for the cross compiler toolchain. See below for more detail.
• LDPATH contains a list of directories where the loader should look for dynamic libraries.
• INIT contains shell variables configuring the init system. See below for more detail.

Utility Functions

For working with configuration files, the following utility functions can be used:

• file_path_override takes a file name and looks for the last layer that contains it. The absolute path of the first found file is echoed.
• cat_file_override looks for the last layer that contains a file and prints it to standard output.
• cat_file_merge prints the content of a file to standard output, for every layer that contains the file, in layer precedence order.
• include_override includes a file using the source builtin from the last layer that contains the file.
• include_merge includes a file using the source builtin from every layer that contains the file, in layer precedence order.

Toolchain Configuration

The toolchain configuration file contains a list of shell variables for configuring the cross toolchain packages, as well as some other packages that need to know information about the target system.

Currently, the following variables are used:

• RELEASEPKG contains the name of the release package to build to trigger a build of the entire system. Typically this package depends on the rootfs package, which in turn pulls all configured packages as dependencies. It gets built last and packages the root filesystem image and boot loader files in some device specific way, so they can be installed easily on the target hardware.
• LINUXPKG contains the name of the kernel package. There is a default package called 'linux' that builds a standard, main line LTS kernel. Other packages can be specified for building vendor kernels.
• TARGET specifies the target triplet for the cross toolchain, which is also the host triplet for packages cross compiled with autotools.
• GCC_CPU specifies the target processor for GCC.
• GCC_EXTRACFG extra configure arguments passed to GCC. For instance, this may contain FPU configuration for ARM targets.
• MUSL_CPU contains the target CPU architecture for the Musl C library.
• LINUX_CPU contains the value of the ARCH variable passed to the kernel build system. Used by the generic main line kernel package.
• LINUX_TGT contains the space seperated make targets for the generic, main line, LTS kernel package.
• OPENSSL_TARGET contains the target architecture for the OpenSSL package.

Init System Configuration

The INIT configuration file contains a list of shell variables for configuring the init system.

Currently, the following variables are used:

• GETTY_TTY contains a space separated list of ttys on which to start agetty on system boot.
• HWCLOCK is set to yes if the system has a hardware clock that the time should be synchronized with during system boot and shutdown. If set to anything else, the init system is configured to keep track of time using ntpdate and a file on persistent storage.
• DHCP_PORTS contains a space separated list of network interfaces on which to operate a DHCP client for network auto configuration.
• SERVICES contains a space separated list of raw service names to enable.
• MODULES contains a space seperated list of kernel modules that should be loaded during system boot.

For configuring network interfaces, a file ifrename exists that assigns persistent, predictable names to network interfaces.

The default naming scheme of the Pygos system is to rename the Ethernet interfaces installed on the board to port where X is an index starting with 0.

For each network interface, addresses, mtu, offloading, etc can be configured in a file interfaces/<name>, where name is the interface name after renaming.

If the files nftables.rules or sysctl.conf are found, they are copied to the target system image and the coresponding services are enabled.

For more details, please refer to the not yet existing network documentation.

Package Specific Configuration Files

Additional configuration files may be present that are used by various packages.

The following files are currently used (with default override behavior):

• linux.config contains the kernel build configuration. The same name is currently used by both the main line and the board specific vendor kernels.
• dnsmasq.conf is installed to /etc by the dnsmasq package.
• unbound.conf is installed to /etc by the unbound package.
• dhcpcd.conf is installed to /etc by the dhcpcd package.