Toolchains

A toolchain is a set of distinct software development tools that are linked (or chained) together by specific stages such as GCC, binutils and glibc (a portion of the GNU Toolchain). Optionally, a toolchain may contain other tools such as a Debugger or a Compiler for a specific programming language, such as ,C++. Quite often, the toolchain used for embedded development is a cross toolchain, or more commonly known as a cross compiler. All the programs (like GCC) run on a host system of a specific architecture (such as x86) but produce binary code (executables) to run on a different architecture (e.g. ARM). This is called cross compilation and is the typical way of building embedded software. It is possible to compile natively, running gcc on your target. Before searching for a prebuilt toolchain or building your own, it's worth checking to see if one is included with your target hardware's Board Support Package (BSP) if you have one.

Introduction
When talking about toolchains, one must distinguish three different machines :
 * the build machine, on which the toolchain is built
 * the host machine, on which the toolchain is executed
 * the target machine, for which the toolchain generates code

From these three different machines, we distinguish four different types of toolchain building processes :
 * A native toolchain, as can be found in normal Linux distributions, has usually been compiled on x86, runs on x86 and generates code for x86.
 * A cross-compilation toolchain, which is the most interesting toolchain type for embedded development, is typically compiled on x86, runs on x86 and generates code for the target architecture (be it ARM, MIPS, PowerPC or any other architecture supported by the different toolchain components)
 * A cross-native toolchain, is a toolchain that has been built on x86, but runs on your target architecture and generates code for your target architecture. It's typically needed when you want a native gcc on your target platform, without building it on your target platform.
 * A canadian build is the process of building a toolchain on machine A, so that it runs on machine B and generates code for machine C. It's usually not really necessary.

Binutils
The GNU Binutils are the first component of a toolchain. The GNU Binutils contains two very important tools :
 * as, the assembler, that turns assembly code (generated by gcc) to binary
 * ld, the linker, that links several object code into a library, or an executable

Binutils also contains a couple of other binary file manipulation or analysis tools, such as objcopy, objdump, nm, readelf, strip, and so on. The Binutils website has some documentation on all these tools.

C, C++, Java, Ada, Fortran, Objective-C compiler
The second major component of a toolchain is the compiler. In the embedded Linux, the only realistic solution today is GCC, the GNU Compiler Collection. Nowadays, as input, it now only supports C, but also C++, Java, Fortran, Objective-C and Ada. As output, it supports a very wide range of architectures.

C library
The C library implements the traditional POSIX API that can be used to develop userspace applications. It interfaces with the kernel through system calls, and provides higher-level services.

Realistically, there are nowadays two options for the C Library:
 * glibc is the C library from the GNU project. It's the C library used by virtually all desktop and server GNU/Linux systems. It's feature-full, portable, complies to standards, but a bit bloated.
 * uClibc is an alternate C library, which features a much smaller footprint. This library can be an interesting alternative if flash space and/or memory footprint is an issue. However, the space advantages gained using uClibc are becoming less important as the price of memory & flash continues to drop. There are a few "gotcha"s when using uClibc. At time of writing(uClibc 0.9.28), locales are a bit ropey and the new Application Binary Interface (ABI) for ARM architectures (EABI) introduced with GCC 4.1.1 requires patches to be applied. This situation is likely to get better quickly as uClibc is under heavy development.

The C library has a special relation with the C compiler, so the choice of the C library must be done when the toolchain is generated. Once the toolchain has been built, it is no longer possible to switch to another library.

Debugger
The debugger is also usually part of the toolchain, as a cross-debugger is needed to debug applications running on your target machine. In the embedded Linux world, the typical debugger is GDB.

Getting a toolchain
There are several ways to get a toolchain :
 * Get a prebuilt toolchain, either from a vendor such as CodeSourcery, or probably inside the Board Support Package shipped with your hardware platform by the vendor. This is the easiest solution, as the toolchain is already built, and has supposedly being tested by the vendor. The drawback is that you don't have flexibility on your toolchain features (which C library ? hard-float or soft-float ? which ABI ?)
 * Build a toolchain on your own. However, this can be a real pain. There are version dependency issues, patches required to make something work etc. etc. Check out this (obsolete) build matrix for crosstool and look at all the red "failed" entries.
 * Build a toolchain using an automated tool. The community has built several scripts or more elaborate systems to ease the process of building a toolchain. This way, the recipes and patches needed to build a toolchain made of particular versions of the various components are shared and easily available.

CodeSourcery
CodeSourcery develops Sourcery G++, an Eclipse based Integrated Development Environment (IDE) that incorporates the GNU Toolchain (gcc, gdb, etc.) for cross development for numerous target architectures. CodeSourcery provides a "lite" version for ARM, Coldfire, MIPS and Power architectures. The toolchains are always very up to date. CodeSourcery contributes enhancements it makes to the GNU Toolchain upstream continually, making it the single largest (by patch count) corporate contributor.

DENX ELDK
The DENX Embedded Linux Development Kit (ELDK) provides a complete and powerful software development environment for embedded and real-time systems. It is available for ARM, PowerPC and MIPS processors and consists of:

* Cross Development Tools (Compiler, Assembler, Linker etc.) to develop software for the target system. * Native Tools (Shell, commands and libraries) which provide a standard Linux development environment that runs on the target system. * Firmware (U-Boot) that can be easily ported to new boards and processors. * Linux kernel including the complete source-code with all device drivers, board-support functions etc. * Xenomai - RTOS Emulation framework for systems requiring hard real-time responses. * SELF (Simple Embedded Linux Framework) as fundament to build your embedded systems on.

All components of the ELDK are available for free with complete source code under GPL and other Free Software Licenses. Also, detailed instructions to rebuild all the tools and packages from scratch are included.

The ELDK can be downloaded for free from several mirror sites or ordered on CD-ROM for a nominal charge (99 Euro). To order the CD please contact office@denx.de

Detailed information about the ELDK is available here.

Scratchbox
Scratchbox provides toolchains for ARM and x86 target architectures (with PowerPC, MIPS and CRIS in experimental stages but aren't making real progress since years, so Scratchbox should probably be considered ARM and x86 only). Both uClibc and glibc are supported.

Scratchbox simplifies cross compiling software which is built using GNU autotools - Code tests performed by configure are run in an emulator or even on the actual target. The toolchains scratchbox ships with are based on gcc 3.3 and as such are quite old, but stable and well tested. It should be pointed out that scripts to build custom toolchains are also provided with scratchbox allowing more recent gcc versions to be used.

Fedora ARM
Fedora ARM is a try to port Fedora to ARM. It provides some tools as an ARM toolchain packaged in RPM format. Link: Fedora ARM

Embedded Debian cross-tools packages
For Debian users, the toolchains problem is fairly reliably solved.

For a debian-based box just install pre-built cross toolchains from emdebian. Instructions are given here: http://www.emdebian.org/tools/crosstools.html

Supported build architectures are: i386, amd64, (and powerpc, ish) Targets insclude nearly all debian-supported architectures Compilers are gcc3.3, 3.4, 4.1, 4.2, 4.3. Lenny and sid are supported although the tools are inevitably slightly behind Debian proper.

http://www.emdebian.org/toolchains/search.php?section=devel gives a (long) listing of available packages.

emdebian-tools also provides the debian equivalent of crosstool ('emchain' to build your own version of current toolchain, should a suitable pre-built one not exist.

Buildroot
Buildroot is a complete build system based on the Linux Kernel configuration system and supports a wide range of target architectures. It generates root file system images ready to be written to flash. In addition to having a huge number of packages which can be compiled into the image, it also generates a cross toolchain to build those packages from source. Even if you don't want to use buildroot for your root filesystem, it is a useful tool for generating a toolchain. It should be noted however that it only supports uClibc. If you want to use glibc, you'll need something else.

Crossdev (Gentoo)
Crossdev is specific to developers using Gentoo for their development PCs. It is a script which generates a cross toolchain using the portage build scripts for gcc etc. There are numerous architectures which are supported and both uClibc and glibc toolchains can be built. Link: Gentoo Cross-Compile HOWTO

Crosstool
Crosstool is probably the first publicly-released script which downloads source tar-balls and builds simple gcc/glibc cross toolchains. Originally written by Dan Kegel, it only supported glibc toolchains, and is now unmaintained.

Crosstool-NG
Crosstool-NG is a well-maintained fork of crosstool, targeted at easier configuration, re-factored code, and a learning base on how toolchains are built, with support for both uClibc and glibc, for debug tools (gdb, strace, dmalloc...), and a wide range of versions for each tools. Different target architectures are supported as well. It offers a kernel-like configuration system to select the different configuration options of the toolchain (component versions, component configuration, etc.). Crosstool-NG has an active and responsive user and developer community.

Crossdev/tsrpm (Timesys)
Crossdev is a project sponsored by Timesys, completely unrelated to the Gentoo cross toolchain generation system. The projects main focus is on a tool called tsrpm which is used to build cross development toolchains and generate cross-compiled software packages. Currently only x86 and select PowerPC architectures are supported. Link: Crossdev

OSELAS.Toolchain
The OSELAS.Toolchain project aims at supplying a complete build system for recent GNU toolchains. It uses the PTXdist build system, a userland build system based on Kconfig. The current version 1.99.3.1 of OSELAS.Toolchain contains support for arm, x86, avr, mips and PowerPC. In addition, there are toolchains for bare metal platforms like Cortex-M3 and AVR-8-Bit. OSELAS.Toolchain contains some further goodies like gcj support for ARM and mingw Support for x86. Link: OSELAS.Toolchain Link: PTXdist

Bitbake
Bitbake is the tool used by OpenEmbedded. There is a bitbake manual at http://bitbake.berlios.de/manual/, but the best way to get started is probably by just building an existing distribution that uses openembedded (e.g. Ångström, see http://www.angstrom-distribution.org/building-%C3%A5ngstr%C3%B6m for details).

ARM
See ARMCompilers