Toolchain and Embedded Distributions
For many embedded applications, the requirements for the processor deviate from those in development workstations. The chosen processor architecture, therefore, usually differs and requires cross development tools to compile the target applications on the workstation. Generating the cross development tools and a suitable environment is certainly not an easy venture. Several projects have, therefore, materialized over time to alleviate the process.
Start from scratch with FSF/OSS sources
Starting from sources is certainly the most challenging approach. It usually requires additional patches and sometimes matching versions of sources.
This project consists of several projects intended to help building a Linux system from sources. The main project resembles a book that describes the build-process in great detail.
crosstool-NG (http://crosstool-ng.org/) provides a system to build a complete toolchain. It supports the c-libraries uClibc, glibc, and eglibc, but can also be used to build a 'bare' toolchain. The current version does not yet support Xtensa as a target, but development is under way. More information about building a toolchain for Xtensa using crosstool-NG can be found here crosstool-NG.
Buildroot is a set of Makefiles and patches that makes it easy to generate a cross-compilation toolchain and root file system for your target Linux system. For build instructions for Xtensa, see Buildroot.
OpenEmbedded (http://openembedded.org) provided a development environment for embedded systems.
From the website:
The Yocto Project is an open source collaboration project that provides templates, tools and methods to help you create custom Linux-based systems for embedded products regardless of the hardware architecture.