Section 5.6. Chapter Summary

5.6. Chapter Summary

• The Linux kernel project is large and complex. Understanding the structure and composition of the final image is key to learning how to customize your own embedded project.

• Many architectures concatenate an architecture-specific bootstrap loader onto the kernel binary image to set up the proper execution environment required by the Linux kernel. We presented the bootstrap loader build steps to differentiate this functionality from the kernel proper.

• Understanding the initialization flow of control will help deepen your knowledge of the Linux kernel and provide insight into how to customize for your particular set of requirements.

• We found the kernel entry point in head.o and followed the flow of control into the first kernel C file, main.c. We looked at a booting system and the messages it produced, along with an overview of many of the important initialization concepts.

• The kernel command line processing and the mechanisms used to declare and process kernel command line parameters was presented. This included a detailed look at some advanced coding techniques for calling arbitrary unknown setup routines using linker-produced tables.

• The final kernel boots steps produce the first userspace processes. Understanding this mechanism and its options will enable you to customize and troubleshoot embedded Linux startup issues.

5.6.1. Suggestions for Additional Reading

GNU Compiler Collection documentation:

http://gcc.gnu.org/onlinedocs/gcc^[11]

^[11] Especially the sections on function attributes, type attributes, and variable attributes.

Using LD, the GNU linker

http://www.gnu.org/software/binutils/manual/ld-2.9.1/ld.html

Kernel documentation:

.../Documentation/kernel-parameters.txt