// -*- mode:doc; -*- // vim: set syntax=asciidoc: == Daily use include::rebuilding-packages.txt[] === Offline builds If you intend to do an offline build and just want to download all sources that you previously selected in the configurator ('menuconfig', 'nconfig', 'xconfig' or 'gconfig'), then issue: -------------------- $ make source -------------------- You can now disconnect or copy the content of your +dl+ directory to the build-host. === Building out-of-tree As default, everything built by Buildroot is stored in the directory +output+ in the Buildroot tree. Buildroot also supports building out of tree with a syntax similar to the Linux kernel. To use it, add +O=+ to the make command line: -------------------- $ make O=/tmp/build -------------------- Or: -------------------- $ cd /tmp/build; make O=$PWD -C path/to/buildroot -------------------- All the output files will be located under +/tmp/build+. If the +O+ path does not exist, Buildroot will create it. *Note:* the +O+ path can be either an absolute or a relative path, but if it's passed as a relative path, it is important to note that it is interpreted relative to the main Buildroot source directory, *not* the current working directory. When using out-of-tree builds, the Buildroot +.config+ and temporary files are also stored in the output directory. This means that you can safely run multiple builds in parallel using the same source tree as long as they use unique output directories. For ease of use, Buildroot generates a Makefile wrapper in the output directory - so after the first run, you no longer need to pass +O=<...>+ and +-C <...>+, simply run (in the output directory): -------------------- $ make -------------------- [[env-vars]] === Environment variables Buildroot also honors some environment variables, when they are passed to +make+ or set in the environment: * +HOSTCXX+, the host C++ compiler to use * +HOSTCC+, the host C compiler to use * +UCLIBC_CONFIG_FILE=+, path to the uClibc configuration file, used to compile uClibc, if an internal toolchain is being built. + Note that the uClibc configuration file can also be set from the configuration interface, so through the Buildroot +.config+ file; this is the recommended way of setting it. + * +BUSYBOX_CONFIG_FILE=+, path to the Busybox configuration file. + Note that the Busybox configuration file can also be set from the configuration interface, so through the Buildroot +.config+ file; this is the recommended way of setting it. + * +BR2_DL_DIR+ to override the directory in which Buildroot stores/retrieves downloaded files + Note that the Buildroot download directory can also be set from the configuration interface, so through the Buildroot +.config+ file; this is the recommended way of setting it. * +BR2_GRAPH_ALT+, if set and non-empty, to use an alternate color-scheme in build-time graphs * +BR2_GRAPH_OUT+ to set the filetype of generated graphs, either +pdf+ (the default), or +png+. * +BR2_GRAPH_DEPS_OPTS+ to pass extra options to the dependency graph; see xref:graph-depends[] for the accepted options An example that uses config files located in the toplevel directory and in your $HOME: -------------------- $ make UCLIBC_CONFIG_FILE=uClibc.config BUSYBOX_CONFIG_FILE=$HOME/bb.config -------------------- If you want to use a compiler other than the default +gcc+ or +g+++ for building helper-binaries on your host, then do -------------------- $ make HOSTCXX=g++-4.3-HEAD HOSTCC=gcc-4.3-HEAD -------------------- === Dealing efficiently with filesystem images Filesystem images can get pretty big, depending on the filesystem you choose, the number of packages, whether you provisioned free space... Yet, some locations in the filesystems images may just be _empty_ (e.g. a long run of 'zeroes'); such a file is called a _sparse_ file. Most tools can handle sparse files efficiently, and will only store or write those parts of a sparse file that are not empty. For example: * +tar+ accepts the +-S+ option to tell it to only store non-zero blocks of sparse files: ** +tar cf archive.tar -S [files...]+ will efficiently store sparse files in a tarball ** +tar xf archive.tar -S+ will efficiently store sparse files extracted from a tarball * +cp+ accepts the +--sparse=WHEN+ option (+WHEN+ is one of +auto+, +never+ or +always+): ** +cp --sparse=always source.file dest.file+ will make +dest.file+ a sparse file if +source.file+ has long runs of zeroes Other tools may have similar options. Please consult their respective man pages. You can use sparse files if you need to store the filesystem images (e.g. to transfer from one machine to another), or if you need to send them (e.g. to the Q&A team). Note however that flashing a filesystem image to a device while using the sparse mode of +dd+ may result in a broken filesystem (e.g. the block bitmap of an ext2 filesystem may be corrupted; or, if you have sparse files in your filesystem, those parts may not be all-zeroes when read back). You should only use sparse files when handling files on the build machine, not when transferring them to an actual device that will be used on the target. === Graphing the dependencies between packages [[graph-depends]] One of Buildroot's jobs is to know the dependencies between packages, and make sure they are built in the right order. These dependencies can sometimes be quite complicated, and for a given system, it is often not easy to understand why such or such package was brought into the build by Buildroot. In order to help understanding the dependencies, and therefore better understand what is the role of the different components in your embedded Linux system, Buildroot is capable of generating dependency graphs. To generate a dependency graph of the full system you have compiled, simply run: ------------------------ make graph-depends ------------------------ You will find the generated graph in +output/graphs/graph-depends.pdf+. If your system is quite large, the dependency graph may be too complex and difficult to read. It is therefore possible to generate the dependency graph just for a given package: ------------------------ make -graph-depends ------------------------ You will find the generated graph in +output/graph/-graph-depends.pdf+. Note that the dependency graphs are generated using the +dot+ tool from the _Graphviz_ project, which you must have installed on your system to use this feature. In most distributions, it is available as the +graphviz+ package. By default, the dependency graphs are generated in the PDF format. However, by passing the +BR2_GRAPH_OUT+ environment variable, you can switch to other output formats, such as PNG, PostScript or SVG. All formats supported by the +-T+ option of the +dot+ tool are supported. -------------------------------- BR2_GRAPH_OUT=svg make graph-depends -------------------------------- The +graph-depends+ behaviour can be controlled by setting options in the +BR2_GRAPH_DEPS_OPTS+ environment variable. The accepted options are: * +--depth N+, +-d N+, to limit the dependency depth to +N+ levels. The default, +0+, means no limit. -------------------------------- BR2_GRAPH_DEPS_OPTS='-d 3' make graph-depends -------------------------------- === Graphing the build duration [[graph-duration]] When the build of a system takes a long time, it is sometimes useful to be able to understand which packages are the longest to build, to see if anything can be done to speed up the build. In order to help such build time analysis, Buildroot collects the build time of each step of each package, and allows to generate graphs from this data. To generate the build time graph after a build, run: ---------------- make graph-build ---------------- This will generate a set of files in +output/graphs+ : * +build.hist-build.pdf+, a histogram of the build time for each package, ordered in the build order. * +build.hist-duration.pdf+, a histogram of the build time for each package, ordered by duration (longest first) * +build.hist-name.pdf+, a histogram of the build time for each package, order by package name. * +build.pie-packages.pdf+, a pie chart of the build time per package * +build.pie-steps.pdf+, a pie chart of the global time spent in each step of the packages build process. This +graph-build+ target requires the Python Matplotlib and Numpy libraries to be installed (+python-matplotlib+ and +python-numpy+ on most distributions), and also the +argparse+ module if you're using a Python version older than 2.7 (+python-argparse+ on most distributions). By default, the output format for the graph is PDF, but a different format can be selected using the +BR2_GRAPH_OUT+ environment variable. The only other format supported is PNG: ---------------- BR2_GRAPH_OUT=png make graph-build ----------------