Trying to understand kernel trap code

[TJ Lee]

Hi,
 
I just started looking at FreeBSD kernel code in more detail and want to understand the low-level entry points into the kernel on a x86-64 CPU. What I'd like to know is precisely what happens when I execute a "syscall" instruction in user-land. More specifically, what instruction in what assembly source file is RIP/CS loaded with on executing syscall? Also where in the source code do we load the MSRs with these values?
 
- tj