A tool chain is basically defined as a compiler, linker and C library (I.e. GCC, binutils & glibc/uClibc). Optionally, a tool chain may contain a debugger and C++ compiler. Quite often, the tool chain used for embedded devices is a cross toolchain: All the programs (like GCC) run on a PC but produce binary code to run on a different architecture (e.g. ARM). This is called cross compilation and is assumed to be what you want to do. It is possible to compile natively, running gcc on your target. However, unless you have an x86 target, you need a tool chain on your device, which eats up your flash and will also take much longer to compile things than your far more powerful PC. Before going down the route of obtaining a toolchain, it's worth checking to see if one is included with your target's Board Support Package (BSP), if you have one.
Note about C libraries
Realistically, there are two options for the C Library: uClibc & glibc. GLibc is what your PC is probably using. It's a bit of a brute, very powerful but a bit bloated. If flash space and memory footprint is an issue, using uClibc is likely to be the better option. 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.
Creating a cross development toolchain from sources can be a real pain. There are version dependency issues, patches required to make something work etc. etc. Check out the build matrix for crosstool and look at all the red "failed" entries. Fortunately, there are several groups of people who have done all the hard work for you, producing scripts to create a toolchain or releases of binary toolchains.
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 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. * RTAI (Real Time Application Interface) Extension 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 firstname.lastname@example.org
Detailed information about the ELDK is available here.
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. Link: Buildroot homepage
Scratchbox provides toolchains for ARM and x86 target architectures (with PowerPC, MIPS and CRIS in experimental stages). Both uClibc & 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. Link: Scratchbox
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 is a script which downloads source tar-balls and builds simple gcc/glibc cross toolchains. There is a build matrix which shows which versions of gcc/glibc work together with various architectures (link). The inclusion of this matrix makes it easy to select which versions of gcc/glibc should be used to generate a toolchain for a particular architecture. Link: Crosstool
Crosstool-NG is a 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. Link: crosstool-NG
Code Sourcery is a commercial company which develops cross development tools for numerous architectures. Code Sourcery provides a "lite" version for their ARM, Coldfire & Power PC architecture development tools which is freely available. The toolchains are usually very up-to-date. Link: Code Sourcery
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