If you're interested in reading more about the various kinds of runtime code patching used in Linux, there was a nice paper on it at last year's Malware Memory Forensics Workshop:

Slides:

https://www.acsac.org/2014/workshops/mmf/ThomasKittel-Code%2...

Paper:

https://www.acsac.org/2014/workshops/mmf/Thomas%20Kittel-%20...