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diff --git a/docs/build.tex b/docs/build.tex new file mode 100644 index 0000000..6e1539a --- /dev/null +++ b/docs/build.tex @@ -0,0 +1,594 @@ +One of the biggest challenges to getting started with embedded devices is that you +cannot just install a copy of Linux and expect to be able to compile a firmware. +Even if you did remember to install a compiler and every development tool offered, +you still would not have the basic set of tools needed to produce a firmware image. +The embedded device represents an entirely new hardware platform, which is +most of the time incompatible with the hardware on your development machine, so in a process called +cross compiling you need to produce a new compiler capable of generating code for +your embedded platform, and then use it to compile a basic Linux distribution to +run on your device. + +The process of creating a cross compiler can be tricky, it is not something that is +regularly attempted and so there is a certain amount of mystery and black magic +associated with it. In many cases when you are dealing with embedded devices you will +be provided with a binary copy of a compiler and basic libraries rather than +instructions for creating your own -- it is a time saving step but at the same time +often means you will be using a rather dated set of tools. Likewise, it is also common +to be provided with a patched copy of the Linux kernel from the board or chip vendor, +but this is also dated and it can be difficult to spot exactly what has been +modified to make the kernel run on the embedded platform. + +\subsection{Building an image} + +OpenWrt takes a different approach to building a firmware; downloading, patching +and compiling everything from scratch, including the cross compiler. To put it +in simpler terms, OpenWrt does not contain any executables or even sources, it is an +automated system for downloading the sources, patching them to work with the given +platform and compiling them correctly for that platform. What this means is that +just by changing the template, you can change any step in the process. + +As an example, if a new kernel is released, a simple change to one of the Makefiles +will download the latest kernel, patch it to run on the embedded platform and produce +a new firmware image -- there is no work to be done trying to track down an unmodified +copy of the existing kernel to see what changes had been made, the patches are +already provided and the process ends up almost completely transparent. This does not +just apply to the kernel, but to anything included with OpenWrt -- It is this one +simple understated concept which is what allows OpenWrt to stay on the bleeding edge +with the latest compilers, latest kernels and latest applications. + +So let's take a look at OpenWrt and see how this all works. + + +\subsubsection{Download OpenWrt} + +OpenWrt can be downloaded via subversion using the following command: + +\begin{Verbatim} +$ svn checkout svn://svn.openwrt.org/openwrt/trunk openwrt-trunk +\end{Verbatim} + +Additionally, there is a trac interface on \href{https://dev.openwrt.org/}{https://dev.openwrt.org/} +which can be used to monitor svn commits and browse the source repository. + + +\subsubsection{The directory structure} + +There are four key directories in the base: + +\begin{itemize} + \item \texttt{tools} + \item \texttt{toolchain} + \item \texttt{package} + \item \texttt{target} +\end{itemize} + +\texttt{tools} and \texttt{toolchain} refer to common tools which will be +used to build the firmware image, the compiler, and the C library. +The result of this is three new directories, \texttt{build\_dir/host}, which is a temporary +directory for building the target independent tools, \texttt{build\_dir/toolchain-\textit{<arch>}*} +which is used for building the toolchain for a specific architecture, and +\texttt{staging\_dir/toolchain-\textit{<arch>}*} where the resulting toolchain is installed. +You will not need to do anything with the toolchain directory unless you intend to +add a new version of one of the components above. + +\begin{itemize} + \item \texttt{build\_dir/host} + \item \texttt{build\_dir/toolchain-\textit{<arch>}*} +\end{itemize} + +\texttt{package} is for exactly that -- packages. In an OpenWrt firmware, almost everything +is an \texttt{.ipk}, a software package which can be added to the firmware to provide new +features or removed to save space. Note that packages are also maintained outside of the main +trunk and can be obtained from subversion using the package feeds system: + +\begin{Verbatim} +$ ./scripts/feeds update +\end{Verbatim} + +Those packages can be used to extend the functionality of the build system and need to be +symlinked into the main trunk. Once you do that, the packages will show up in the menu for +configuration. You would do something like this: + +\begin{Verbatim} +$ ./scripts/feeds search nmap +Search results in feed 'packages': +nmap Network exploration and/or security auditing utility + +$ ./scripts/feeds install nmap +\end{Verbatim} + +To include all packages, issue the following command: + +\begin{Verbatim} +$ make package/symlinks +\end{Verbatim} + +\texttt{target} refers to the embedded platform, this contains items which are specific to +a specific embedded platform. Of particular interest here is the "\texttt{target/linux}" +directory which is broken down by platform \textit{<arch>} and contains the patches to the +kernel, profile config, for a particular platform. There's also the "\texttt{target/image}" directory +which describes how to package a firmware for a specific platform. + +Both the target and package steps will use the directory "\texttt{build\_dir/\textit{<arch>}}" +as a temporary directory for compiling. Additionally, anything downloaded by the toolchain, +target or package steps will be placed in the "\texttt{dl}" directory. + +\begin{itemize} + \item \texttt{build\_dir/\textit{<arch>}} + \item \texttt{dl} +\end{itemize} + +\subsubsection{Building OpenWrt} + +While the OpenWrt build environment was intended mostly for developers, it also has to be +simple enough that an inexperienced end user can easily build his or her own customized firmware. + +Running the command "\texttt{make menuconfig}" will bring up OpenWrt's configuration menu +screen, through this menu you can select which platform you're targeting, which versions of +the toolchain you want to use to build and what packages you want to install into the +firmware image. Note that it will also check to make sure you have the basic dependencies for it +to run correctly. If that fails, you will need to install some more tools in your local environment +before you can begin. + +Similar to the linux kernel config, almost every option has three choices, +\texttt{y/m/n} which are represented as follows: + +\begin{itemize} + \item{\texttt{<*>} (pressing y)} \\ + This will be included in the firmware image + \item{\texttt{<M>} (pressing m)} \\ + This will be compiled but not included (for later install) + \item{\texttt{< >} (pressing n)} \\ + This will not be compiled +\end{itemize} + +After you've finished with the menu configuration, exit and when prompted, save your +configuration changes. + +If you want, you can also modify the kernel config for the selected target system. +simply run "\texttt{make kernel\_menuconfig}" and the build system will unpack the kernel sources +(if necessary), run menuconfig inside of the kernel tree, and then copy the kernel config +to \texttt{target/linux/\textit{<platform>}/config} so that it is preserved over +"\texttt{make clean}" calls. + +To begin compiling the firmware, type "\texttt{make}". By default +OpenWrt will only display a high level overview of the compile process and not each individual +command. + +\subsubsection{Example:} + +\begin{Verbatim} +make[2] toolchain/install +make[3] -C toolchain install +make[2] target/compile +make[3] -C target compile +make[4] -C target/utils prepare + +[...] +\end{Verbatim} + +This makes it easier to monitor which step it's actually compiling and reduces the amount +of noise caused by the compile output. To see the full output, run the command +"\texttt{make V=99}". + +During the build process, buildroot will download all sources to the "\texttt{dl}" +directory and will start patching and compiling them in the "\texttt{build\_dir/\textit{<arch>}}" +directory. When finished, the resulting firmware will be in the "\texttt{bin}" directory +and packages will be in the "\texttt{bin/packages}" directory. + + +\subsection{Creating packages} + +One of the things that we've attempted to do with OpenWrt's template system is make it +incredibly easy to port software to OpenWrt. If you look at a typical package directory +in OpenWrt you'll find several things: + +\begin{itemize} + \item \texttt{package/\textit{<name>}/Makefile} + \item \texttt{package/\textit{<name>}/patches} + \item \texttt{package/\textit{<name>}/files} +\end{itemize} + +The patches directory is optional and typically contains bug fixes or optimizations to +reduce the size of the executable. The package makefile is the important item, provides +the steps actually needed to download and compile the package. + +The files directory is also optional and typicall contains package specific startup scripts or default configuration files that can be used out of the box with OpenWrt. + +Looking at one of the package makefiles, you'd hardly recognize it as a makefile. +Through what can only be described as blatant disregard and abuse of the traditional +make format, the makefile has been transformed into an object oriented template which +simplifies the entire ordeal. + +Here for example, is \texttt{package/bridge/Makefile}: + +\begin{Verbatim}[frame=single,numbers=left] + +include $(TOPDIR)/rules.mk + +PKG_NAME:=bridge +PKG_VERSION:=1.0.6 +PKG_RELEASE:=1 + +PKG_SOURCE:=bridge-utils-$(PKG_VERSION).tar.gz +PKG_SOURCE_URL:=@SF/bridge +PKG_MD5SUM:=9b7dc52656f5cbec846a7ba3299f73bd +PKG_CAT:=zcat + +PKG_BUILD_DIR:=$(BUILD_DIR)/bridge-utils-$(PKG_VERSION) + +include $(INCLUDE_DIR)/package.mk + +define Package/bridge + SECTION:=net + CATEGORY:=Base system + TITLE:=Ethernet bridging configuration utility + URL:=http://bridge.sourceforge.net/ +endef + +define Package/bridge/description + Manage ethernet bridging: + a way to connect networks together to form a larger network. +endef + +define Build/Configure + $(call Build/Configure/Default, \ + --with-linux-headers="$(LINUX_DIR)" \ + ) +endef + +define Package/bridge/install + $(INSTALL_DIR) $(1)/usr/sbin + $(INSTALL_BIN) $(PKG_BUILD_DIR)/brctl/brctl $(1)/usr/sbin/ +endef + +$(eval $(call BuildPackage,bridge)) +\end{Verbatim} + +As you can see, there's not much work to be done; everything is hidden in other makefiles +and abstracted to the point where you only need to specify a few variables. + +\begin{itemize} + \item \texttt{PKG\_NAME} \\ + The name of the package, as seen via menuconfig and ipkg + \item \texttt{PKG\_VERSION} \\ + The upstream version number that we are downloading + \item \texttt{PKG\_RELEASE} \\ + The version of this package Makefile + \item \texttt{PKG\_SOURCE} \\ + The filename of the original sources + \item \texttt{PKG\_SOURCE\_URL} \\ + Where to download the sources from (no trailing slash), you can add multiple download sources by separating them with a \\ and a carriage return. + \item \texttt{PKG\_MD5SUM} \\ + A checksum to validate the download + \item \texttt{PKG\_CAT} \\ + How to decompress the sources (zcat, bzcat, unzip) + \item \texttt{PKG\_BUILD\_DIR} \\ + Where to compile the package +\end{itemize} + +The \texttt{PKG\_*} variables define where to download the package from; +\texttt{@SF} is a special keyword for downloading packages from sourceforge. There is also +another keyword of \texttt{@GNU} for grabbing GNU source releases. If any of the above mentionned download source fails, the OpenWrt mirrors will be used as source. + +The md5sum (if present) is used to verify the package was downloaded correctly and +\texttt{PKG\_BUILD\_DIR} defines where to find the package after the sources are +uncompressed into \texttt{\$(BUILD\_DIR)}. + +At the bottom of the file is where the real magic happens, "BuildPackage" is a macro +set up by the earlier include statements. BuildPackage only takes one argument directly -- +the name of the package to be built, in this case "\texttt{bridge}". All other information +is taken from the define blocks. This is a way of providing a level of verbosity, it's +inherently clear what the contents of the \texttt{description} template in +\texttt{Package/bridge} is, which wouldn't be the case if we passed this information +directly as the Nth argument to \texttt{BuildPackage}. + +\texttt{BuildPackage} uses the following defines: + +\textbf{\texttt{Package/\textit{<name>}}:} \\ + \texttt{\textit{<name>}} matches the argument passed to buildroot, this describes + the package the menuconfig and ipkg entries. Within \texttt{Package/\textit{<name>}} + you can define the following variables: + + \begin{itemize} + \item \texttt{SECTION} \\ + The section of package (currently unused) + \item \texttt{CATEGORY} \\ + Which menu it appears in menuconfig: Network, Sound, Utilities, Multimedia ... + \item \texttt{TITLE} \\ + A short description of the package + \item \texttt{URL} \\ + Where to find the original software + \item \texttt{MAINTAINER} (optional) \\ + Who to contact concerning the package + \item \texttt{DEPENDS} (optional) \\ + Which packages must be built/installed before this package. To reference a dependency defined in the + same Makefile, use \textit{<dependency name>}. If defined as an external package, use + \textit{+<dependency name>}. For a kernel version dependency use: \textit{@LINUX\_2\_<minor version>} + \item \texttt{BUILDONLY} (optional) \\ + Set this option to 1 if you do NOT want your package to appear in menuconfig. + This is useful for packages which are only used as build dependencies. + \end{itemize} + +\textbf{\texttt{Package/\textit{<name>}/conffiles} (optional):} \\ + A list of config files installed by this package, one file per line. + +\textbf{\texttt{Build/Prepare} (optional):} \\ + A set of commands to unpack and patch the sources. You may safely leave this + undefined. + +\textbf{\texttt{Build/Configure} (optional):} \\ + You can leave this undefined if the source doesn't use configure or has a + normal config script, otherwise you can put your own commands here or use + "\texttt{\$(call Build/Configure/Default,\textit{<first list of arguments, second list>})}" as above to + pass in additional arguments for a standard configure script. The first list of arguments will be passed + to the configure script like that: \texttt{--arg 1} \texttt{--arg 2}. The second list contains arguments that should be + defined before running the configure script such as autoconf or compiler specific variables. + + To make it easier to modify the configure command line, you can either extend or completely override the following variables: + \begin{itemize} + \item \texttt{CONFIGURE\_ARGS} \\ + Contains all command line arguments (format: \texttt{--arg 1} \texttt{--arg 2}) + \item \texttt{CONFIGURE\_VARS} \\ + Contains all environment variables that are passed to ./configure (format: \texttt{NAME="value"}) + \end{itemize} + +\textbf{\texttt{Build/Compile} (optional):} \\ + How to compile the source; in most cases you should leave this undefined. + + As with \texttt{Build/Configure} there are two variables that allow you to override + the make command line environment variables and flags: + \begin{itemize} + \item \texttt{MAKE\_FLAGS} \\ + Contains all command line arguments (typically variable overrides like \texttt{NAME="value"} + \item \texttt{MAKE\_VARS} \\ + Contains all environment variables that are passed to the make command + \end{itemize} + +\textbf{\texttt{Build/InstallDev} (optional):} \\ + If your package provides a library that needs to be made available to other packages, + you can use the \texttt{Build/InstallDev} template to copy it into the staging directory + which is used to collect all files that other packages might depend on at build time. + When it is called by the build system, two parameters are passed to it. \texttt{\$(1)} points to + the regular staging dir, typically \texttt{staging\_dir/\textit{ARCH}}, while \texttt{\$(2)} points + to \texttt{staging\_dir/host}. The host staging dir is only used for binaries, which are + to be executed or linked against on the host and its \texttt{bin/} subdirectory is included + in the \texttt{PATH} which is passed down to the build system processes. + Please use \texttt{\$(1)} and \texttt{\$(2)} here instead of the build system variables + \texttt{\$(STAGING\_DIR)} and \texttt{\$(STAGING\_DIR\_HOST)}, because the build system behavior + when staging libraries might change in the future to include automatic uninstallation. + +\textbf{\texttt{Package/\textit{<name>}/install}:} \\ + A set of commands to copy files out of the compiled source and into the ipkg + which is represented by the \texttt{\$(1)} directory. Note that there are currently + 4 defined install macros: + \begin{itemize} + \item \texttt{INSTALL\_DIR} \\ + install -d -m0755 + \item \texttt{INSTALL\_BIN} \\ + install -m0755 + \item \texttt{INSTALL\_DATA} \\ + install -m0644 + \item \texttt{INSTALL\_CONF} \\ + install -m0600 + \end{itemize} + +The reason that some of the defines are prefixed by "\texttt{Package/\textit{<name>}}" +and others are simply "\texttt{Build}" is because of the possibility of generating +multiple packages from a single source. OpenWrt works under the assumption of one +source per package Makefile, but you can split that source into as many packages as +desired. Since you only need to compile the sources once, there's one global set of +"\texttt{Build}" defines, but you can add as many "Package/<name>" defines as you want +by adding extra calls to \texttt{BuildPackage} -- see the dropbear package for an example. + +After you have created your \texttt{package/\textit{<name>}/Makefile}, the new package +will automatically show in the menu the next time you run "make menuconfig" and if selected +will be built automatically the next time "\texttt{make}" is run. + +\subsection{Creating binary packages} + +You might want to create binary packages and include them in the resulting images as packages. +To do so, you can use the following template, which basically sets to nothing the Configure and +Compile templates. + +\begin{Verbatim}[frame=single,numbers=left] + +include $(TOPDIR)/rules.mk + +PKG_NAME:=binpkg +PKG_VERSION:=1.0 +PKG_RELEASE:=1 + +PKG_SOURCE:=binpkg-$(PKG_VERSION).tar.gz +PKG_SOURCE_URL:=http://server +PKG_MD5SUM:=9b7dc52656f5cbec846a7ba3299f73bd +PKG_CAT:=zcat + +include $(INCLUDE_DIR)/package.mk + +define Package/binpkg + SECTION:=net + CATEGORY:=Network + TITLE:=Binary package +endef + +define Package/bridge/description + Binary package +endef + +define Build/Configure +endef + +define Build/Compile +endef + +define Package/bridge/install + $(INSTALL_DIR) $(1)/usr/sbin + $(INSTALL_BIN) $(PKG_BUILD_DIR)/* $(1)/usr/sbin/ +endef + +$(eval $(call BuildPackage,bridge)) +\end{Verbatim} + +Provided that the tarball which contains the binaries reflects the final +directory layout (/usr, /lib ...), it becomes very easy to get your package +look like one build from sources. + +Note that using the same technique, you can easily create binary pcakages +for your proprietary kernel modules as well. + +\subsection{Creating kernel modules packages} + +The OpenWrt distribution makes the distinction between two kind of kernel modules, those coming along with the mainline kernel, and the others available as a separate project. We will see later that a common template is used for both of them. + +For kernel modules that are part of the mainline kernel source, the makefiles are located in \textit{package/kernel/modules/*.mk} and they appear under the section "Kernel modules" + +For external kernel modules, you can add them to the build system just like if they were software packages by defining a KernelPackage section in the package makefile. + +Here for instance the Makefile for the I2C subsytem kernel modules : + +\begin{Verbatim}[frame=single,numbers=left] + +I2CMENU:=I2C Bus + +define KernelPackage/i2c-core + TITLE:=I2C support + DESCRIPTION:=Kernel modules for i2c support + SUBMENU:=$(I2CMENU) + KCONFIG:=CONFIG_I2C_CORE CONFIG_I2C_DEV + FILES:=$(MODULES_DIR)/kernel/drivers/i2c/*.$(LINUX_KMOD_SUFFIX) + AUTOLOAD:=$(call AutoLoad,50,i2c-core i2c-dev) +endef +$(eval $(call KernelPackage,i2c-core)) +\end{Verbatim} + +To group kernel modules under a common description in menuconfig, you might want to define a \textit{<description>MENU} variable on top of the kernel modules makefile. + +\begin{itemize} + \item \texttt{TITLE} \\ + The name of the module as seen via menuconfig + \item \texttt{DESCRIPTION} \\ + The description as seen via help in menuconfig + \item \texttt{SUBMENU} \\ + The sub menu under which this package will be seen + \item \texttt{KCONFIG} \\ + Kernel configuration option dependency. For external modules, remove it. + \item \texttt{FILES} \\ + Files you want to inlude to this kernel module package, separate with spaces. + \item \texttt{AUTOLOAD} \\ + Modules that will be loaded automatically on boot, the order you write them is the order they would be loaded. +\end{itemize} + +After you have created your \texttt{package/kernel/modules/\textit{<name>}.mk}, the new kernel modules package +will automatically show in the menu under "Kernel modules" next time you run "make menuconfig" and if selected +will be built automatically the next time "\texttt{make}" is run. + +\subsection{Conventions} + +There are a couple conventions to follow regarding packages: + +\begin{itemize} + \item \texttt{files} + \begin{enumerate} + \item configuration files follow the convention \\ + \texttt{\textit{<name>}.conf} + \item init files follow the convention \\ + \texttt{\textit{<name>}.init} + \end{enumerate} + \item \texttt{patches} + \begin{enumerate} + \item patches are numerically prefixed and named related to what they do + \end{enumerate} +\end{itemize} + +\subsection{Troubleshooting} + +If you find your package doesn't show up in menuconfig, try the following command to +see if you get the correct description: + +\begin{Verbatim} + TOPDIR=$PWD make -C package/<name> DUMP=1 V=99 +\end{Verbatim} + +If you're just having trouble getting your package to compile, there's a few +shortcuts you can take. Instead of waiting for make to get to your package, you can +run one of the following: + +\begin{itemize} + \item \texttt{make package/\textit{<name>}/clean V=99} + \item \texttt{make package/\textit{<name>}/install V=99} +\end{itemize} + +Another nice trick is that if the source directory under \texttt{build\_dir/\textit{<arch>}} +is newer than the package directory, it won't clobber it by unpacking the sources again. +If you were working on a patch you could simply edit the sources under the +\texttt{build\_dir/\textit{<arch>}/\textit{<source>}} directory and run the install command above, +when satisfied, copy the patched sources elsewhere and diff them with the unpatched +sources. A warning though - if you go modify anything under \texttt{package/\textit{<name>}} +it will remove the old sources and unpack a fresh copy. + +Other useful targets include: + +\begin{itemize} + \item \texttt{make package/\textit{<name>}/prepare V=99} + \item \texttt{make package/\textit{<name>}/compile V=99} + \item \texttt{make package/\textit{<name>}/configure V=99} +\end{itemize} + + +\subsection{Using build environments} +OpenWrt provides a means of building images for multiple configurations +which can use multiple targets in one single checkout. These \emph{environments} +store a copy of the .config file generated by \texttt{make menuconfig} and the contents +of the \texttt{./files} folder. +The script \texttt{./scripts/env} is used to manage these environments, it uses +\texttt{git} (which needs to be installed on your system) as backend for version control. + +The command +\begin{Verbatim} + ./scripts/env help +\end{Verbatim} +produces a short help text with a list of commands. + +To create a new environment named \texttt{current}, run the following command +\begin{Verbatim} + ./scripts/env new current +\end{Verbatim} +This will move your \texttt{.config} file and \texttt{./files} (if it exists) to +the \texttt{env/} subdirectory and create symlinks in the base folder. + +After running make menuconfig or changing things in files/, your current state will +differ from what has been saved before. To show these changes, use: +\begin{Verbatim} + ./scripts/env diff +\end{Verbatim} + +If you want to save these changes, run: +\begin{Verbatim} + ./scripts/env save +\end{Verbatim} +If you want to revert your changes to the previously saved copy, run: +\begin{Verbatim} + ./scripts/env revert +\end{Verbatim} + +If you want, you can now create a second environment using the \texttt{new} command. +It will ask you whether you want to make it a clone of the current environment (e.g. +for minor changes) or if you want to start with a clean version (e.g. for selecting +a new target). + +To switch to a different environment (e.g. \texttt{test1}), use: +\begin{Verbatim} + ./scripts/env switch test1 +\end{Verbatim} + +To rename the current branch to a new name (e.g. \texttt{test2}), use: +\begin{Verbatim} + ./scripts/env rename test2 +\end{Verbatim} + +If you want to get rid of environment switching and keep everything in the base directory +again, use: +\begin{Verbatim} + ./scripts/env clear +\end{Verbatim} |