I needed to design, implement and build a loadable kernel module in order to access the ARM11 performance counters from user-space. I will slowly roll out the design and code for the kernel module. But, first, I’ve posted my notes for building a loadable kernel module. It’s easier to explain the process of building the module and the internal design of the module if I separate the two discussions.

There were a few problems along the way. The kernel source for Raspbian Wheezy 3.6.11+ is not available using Synaptic. Only 3.6.9 is available through Synaptic. I needed to download the source for 3.6.11+ from github.com in order to match the installed Linux image. Next, I needed the module version information for 3.6.11+. Usually this information is built along with the kernel and is stored in the file named Module.symvers. Raspbian Wheezy takes 10+ hours to build on the Raspberry Pi, according to reports on the Web, so I didn’t want to undertake a long-running kernel build just to generate the version information. Fortunately, I could download Module.symvers from github.com, too.

I hope the next Raspbian Wheezy distro has all of the essentials for a module build — headers, version information, the whole she-bang. This would really help a brother out because many people are building custom hardware for the RPi and they need to build custom device drivers, too.

I’m currently in the process of writing pages on performance monitoring on the RPi. That discussion will include the design and code for my kernel module. The kernel module is about as simple as can be and is a kind of “Hello world” example. Please stay tuned.