Where is the source to the system calls?

[Dan Strick]

Does anyone know where the system calls are really defined?
I followed open() to _open() to __sys_open() which seems
to be part of something called libc_r before I ran into a
blank wall.  I grepped all of the regular files in /usr/src
and /usr/include and turned up nothing.  I even tried
grepping for open in the output of "nm -g /usr/lib/libc.a".
There is no __sys_open() in libc.  Am I dealing with
C-compiler magic?  Secret macro instructions invoking
undocumented gnu C-compiler asm() features?  A CIA plot?

Is any of this low level structure documented anywhere?

Dan Strick
strick at covad.net