Toolchain and Embedded Distributions
Because Xtensa is a configurable and extensible processor architecture that allows to define additional registers and instructions, the toolchain is the main software component that usually needs to be adapted for a specific Xtensa processor configuration. Tensilica provides a small set of configuration files in form of an overlay that replace the versions in the toolchain sources. The Toolchain Overlay File is a version of that overlay provided by Tensilica with a specific format required for crosstool-NG and buildroot. A script to convert the overlay provided by Tensilica can be found under Toolchain Overlay File
Start from scratch with FSF/OSS sources
Creating a toolchain and bootable root file system starting from sources is certainly the most challenging approach. It usually requires additional patches and sometimes matching versions of sources. While support for Xtensa is integrated in most toolchain tools, they must be patches for a specific Xtensa processor configuration. The overlay metioned above includes a necessary set of configuration files together with information explaining the process to patch the toolchain sources.
crosstool-NG (http://crosstool-ng.org/) provides a system to build a complete toolchain. It supports various C-libraries (Multilib, 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 a development version can be retrieved from the local GIT repositories. The process of patching the toolchain and other architecture specific software is fully automated using the Toolchain Overlay File. More information for building a toolchain for Xtensa using crosstool-NG can be found here.
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. The Xtensa architecture is fully supported in the official tree, including support for specific processor configuration using the Toolchain Overlay File. For build instructions, see Buildroot.