HelenOS sources

__syscall2         54 uspace/lib/c/include/libc.h 	__syscall2(p1, p2, 0, 0, 0, 0, id)
__syscall2         54 uspace/lib/posix/include/libc/libc.h 	__syscall2(p1, p2, 0, 0, 0, 0, id)
HelenOS homepage, sources at GitHub