15.1. Why Build from Source?

The RTEMS Source Builder is not a replacement for the binary install systems you have with commercial operating systems or open source operating system distributions. Those products and distributions are critically important and are the base that allows the RSB to work. The RTEMS Source Builder sits somewhere between you manually entering the commands to build a tool set and a tool such as yum or apt-get to install binary packages made specifically for your host operating system. Building manually or installing a binary package from a remote repository are valid and real alternatives. The RSB provides the specific service of repeatably being able to build tool sets from source code. The process leaves you with the source code used to build the tools and the ability to rebuild it.

If you are developing a system or product that has a long shelf life or is used in a critical piece of infrastructure that has a long life cycle being able to build from source is important. It insulates the project from the fast ever changing world of the host development machines. If your tool set is binary and you have lost the ability to build it you have lost a degree of control and flexibility open source gives you. Fast moving host environments are fantastic. We have powerful multi-core computers with huge amounts of memory and state of the art operating systems your development uses however the product or project you are part of may need to be maintained well past the life time of these host. Being able to build from source is an important and critical part of this process because you can move to a newer host and create an equivalent tool set.

Building from source provides you with control over the configuration of the package you are building. If all or the most important dependent parts are built from source you limit the exposure to host variations. For example the GNU Compiler Collection (GCC) currently uses a number of third-party libraries internally (GMP, ISL, MPC, MPFR, etc.). If your validated compiler generating code for your target processor is dynamically linked against the host’s version of these libraries any change in the host’s configuration may effect you. The changes the host’s package management system makes may be perfectly reasonable in relation to the distribution being managed however this may not extend to you and your tools. Building your tools from source and controlling the specific version of these dependent parts means you are not exposing yourself to unexpected and often difficult to resolve problems. On the other side you need to make sure your tools build and work with newer versions of the host operating system. Given the stability of standards based libraries like libc and ever improving support for standard header file locations this task is becoming easier.

The RTEMS Source Builder is designed to be audited and incorporated into a project’s verification and validation process. If your project is developing critical applications that needs to be traced from source to executable code in the target, you need to also consider the tools and how to track them.

If your IT department maintains all your computers and you do not have suitable rights to install binary packages, building from source lets you create your own tool set that you install under your home directory. Avoiding installing any extra packages as a super user is always helpful in maintaining a secure computing environment.