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Bring documentation somewhat up to date
Signed-off-by: David Oberhollenzer <goliath@infraroot.at>
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docs/build.md
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docs/build.md
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# The Pygos Build System
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The Pygos system can be built by running the `mk.sh` shell script with
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the desired product configuration as argument.
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The Pygos build system creates a number of binary packages from a set of
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source packages using a cross toolchain, installs them to a compressed file
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system image and neatly packages it with an install script for the target
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board.
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The Pygos system can be built by running the `mk.sh` shell script in the root
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of the git tree, with the desired product configuration as argument.
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The shell script can be run from anywhere on the file system. All
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configuration files and scripts are accessed relative to the source location
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of the script and all generated files are accessed relative to the current
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working directory.
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Actually it is even strongly encouraged to run the build system from outside
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the git tree to have the generated files cleanly separated from the build
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system.
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It is strongly encouraged to run the build system from outside the git tree to
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have the generated files cleanly separated from the build system.
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A second script named `check_update.sh` is provided to automatically query
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all upstream package sources to check if newer versions are available.
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The `mk.sh` creates a `download` and a `src` directory. In the former it stores
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downloaded package tar balls, in the later it extracts the tar balls and
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applies patches.
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downloaded source tar balls, in the later it extracts the tar balls and applies
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patches.
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For all other files and directories, a sub directory named after the product
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configuration is created. Throughout the build system, this directory is
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referred to as *build root*.
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configuration is created, referred to as *build root*.
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Inside the build root a `deploy` directory is created. Build output for each
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package is deployed to a sub directory named after the package.
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Inside the build root the directories `log`, `repo` and `toolchain` are
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created. The compiled binary packages are stored in `repo`, the cross
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toolchain is stored in `toolchain`. Outputs and diagnostic messages of the
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build processes are stored in `log` and are each compressed after successfully
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building a package.
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The cross toolchain is stored in `<build root>/toolchain`.
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Outputs and diagnostic messages of the build processes are stored in
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`<build root>/toolchain/log/<package>-<stage>.log`.
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If you are in a real hurry in building the system, you may wish to store the
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input git tree and output build directory on an SSD and create the build root
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directory ahead of time with a tmpfs mounted to it.
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## Packages and Dependcies
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The build system distinguishes between binary packages and source packages.
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A binary package is an archive containing files and meta data, such as
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dependency information. Installing a binary package means extracting its
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contents (and recursively that of its dependencies) to a target location.
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A source package is at its minimum a shell script that is run by the build
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system to produce binary packages. A source package can produce more than one
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binary package (e.g. a program, its utility libraries and development headers
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for the libraries could all be packaged separately).
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Running a build script may require development headers and libraries of other
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packages to be installed to an intermediate staging sysroot used by the cross
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toolchain. Thus, a source package can itself depend on binary packages that
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have to be built first and are installed to the staging sysroot before
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the build process begins. The resulting binary packages can have a completely
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different set of dependencies (e.g. they don't need the library headers).
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For simplicity, the cross toolchain, rootfs image and packaging are also
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implemented as source packages and the build system takes care of building
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everything in the right order.
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## Package Build Scripts
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The directory `pkg` contains a sub directory for each package. Each package
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directory is expected to contain a shell script named `build`.
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The directory `pkg` contains a sub directory for each source package. Each
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package directory is expected to contain a shell script named `build`.
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The build script is expected to set the following variables:
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* `VERSION` containing a package version number.
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* `URL` containig a URL from which to download a source tar ball.
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* `URL` containing a URL from which to download a source tar ball.
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* `TARBALL` containing the name of the source tar ball. This is appended to
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the URL to download the package.
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* `SHA256SUM` containing the SHA-256 check sum of the source tar ball.
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* `SRCDIR` containing the name of the source directory unpacked from the
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tar ball.
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* `DEPENDS` containing a space separated list of packages that the package
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in question depends on. Those packages are built first. Their headers and
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libraries are copied into the cross toolchain before building the current
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package and removed after building it.
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Using the specified variables, the build system automatically downloads,
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verifies and unpacks the source tar balls (unless that has already been done)
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and determines the order in which to build the packages.
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* `DEPENDS` containing a space separated list of packages that have to be built
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first and installed to the cross toolchains sysroot.
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* `SUBPKG` containing a space sperated list of binary packages produced. If
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left empty, the build system assumes one binary package with the same name
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as the source package.
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The `build` script is also expected to implement the following functions:
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@ -65,38 +89,52 @@ The `build` script is also expected to implement the following functions:
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* `prepare` is run after unpacking the source tar ball. The current working
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directory is set to the source directory. The path to the package directory
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is passed as first argument, so the function can easily access patch files
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stored in the package directory. All output and error messages from the
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script are stored in `<packagename>-prepare.log`.
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stored in the package directory.
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* `build` is run to compile the package. The current working directory is a
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temporary directory inside the build root directory. The source directory
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is passed as first argument. The second argument is a path to the *deploy*
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directory where generated files are installed. All standard output and error
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messages from the script are piped to `<packagename>-build.log`.
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* `deploy` is run after compilation to install the build output to the deploy
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directory. Arguments and working directory are the same as for `build`. All
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output and error messages from the script are piped to
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`<packagename>-deploy.log`. The `deploy` function is also expected to
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generate a file named `rootfs_files.txt` that contains a listing of all files
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in the deploy directory that should be included in the root filesystem and
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what permissions should be set on them. Once the function returns,
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the `mk.sh` script strips everything installed to `bin` and `lib`, so the
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implementation doesn't have to do that. In fact `install-strip` Makefile
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targets should not be used since many implementations are broken for cross
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compilation. Further common steps are executed for packages that
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produce `libtool` archives and `pkg-config` files.
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is passed as first argument.
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* `deploy` is run after compilation to install the build output to a staging
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directory. Arguments and working directory are the same as for `build`.
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The function is expected to generate a `*.files` and a `*.desc` file for
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each sub package, so the build system can automatically package it.
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* `check_update` is only used by the `check_update.sh` script. It is supposed
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to find out if the package has a newer version available, and if so, echo it
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to stdout.
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### Environment Variables
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### Directory Variables
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The `mk.sh` sets a number of shell variables that package scripts can use.
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A number of directories exist that can be accessed through global variables
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from package build scripts.
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The following shell variables are globally visible and identify special
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directories that build scripts might be interested in:
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* `SCRIPTDIR` points to the git tree containging the build system.
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* `PKGDOWNLOADDIR` points to the directory to which source tar balls
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are downloaded.
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* `PKGSRCDIR` points to the directory into which source tar balls are unpacked.
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* `BUILDROOT` points to the build root directory.
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* `PKGLOGDIR` points to the directory where log files are written to stored.
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* `REPODIR` points to the directory where binary packages are stored.
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* `TCDIR` points to the cross toolchain directory.
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While building a package, additional staging directories are temporarily
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created inside the build root directory:
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* `PKGBUILDDIR` points to a temporary directory inside the build root that is
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used as working directory for the `build` and `deploy` functions.
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* `PKGDEPLOYDIR` points to another such temporary directory that the `deploy`
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function is expected to install binaries to.
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### Additional Variables
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The following variables describe the target system and the build environment:
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* `BOARD` contains the target board specified on the command line
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* `PRODUCT` contains the product name specified on the command line
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* `LAYERCONF` contains path to the list of active configuration layers for the
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target product
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* `TARGET` specifies the host triplet of the target board
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* `OS_NAME` is statically set to `Pygos`
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* `OS_RELEASE` holds a version string generated using `git-describe`
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is running on for compiling toolchain packages.
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* `CMAKETCFILE` contains the absolute path to a CMake toolchain file that can
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be used for compiling CMake based packages with the cross toolchain.
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And a number of variables containing special directories:
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* `BUILDROOT` contains the absolute path to the build root directory, i.e. the
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output directory within the working directory of the `mk.sh` script.
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* `SCRIPTDIR` contains the absolute path to the script directory, i.e. the git
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tree with the build system in it.
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* `TCDIR` contains the absolute path to the cross toolchain directory.
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* `PKGBUILDDIR` contains the absolute path of the temporary directory in which
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the package is being built.
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* `PKGSRCDIR` contains the root directory of all unpacked package tar balls
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* `PKGDEPLOYDIR` contains the root directory of all package deploy directories
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* `PKGLOGDIR` holds the absolute path of the directory containing all log files
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* `PKGDOWNLOADDIR` holds the absolute path of the directory containing all
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package tar balls
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* `PACKAGELIST`, `DEPENDSLIST`, `PROVIDESLIST` hold data used internally for
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dependency management.
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The cross toolchain directory containing the executable prefixed with `$TARGET-`
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is also prepended to `PATH`.
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* `strip_files` takes a list of files as argument and runs the cross toolchain
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strip program on those that are valid ELF binaries. If a directory is
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encountered, the function recursively processes the sub directory. Usually
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you don't need to use this. The `mk.sh` script uses this function to after
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you don't need to use this. The `mk.sh` script uses this function after
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the deploy step to process the `bin` and `lib` directories.
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* `unfuck_libtool` may have to be used before running `make install` on
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packages that build shared libraries with libtool. GNU libtool is an utter
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piece of garbage from hell. This function removes the global `/lib` search
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path from the `*.la` files, so libtool doesn't crap itself during its stupid
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relink phase, trying to link against libraries from the host system, after
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already successfully cross compiling the libraries.
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* `verson_find_greatest` can be used in `check_update` to find the largest
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version number from a list. The list of version numbers is read from stdin.
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Version numbers can have up to four dot separated numbers or characters.
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* `run_configure` can be used to run `autoconf` generated `configure` scripts
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with all the required options set for cross compilation. Extra options can
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be to the options passed to `configure`.
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be added to the options passed to `configure`.
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## Configuration Files
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