HelenOS sources

__syscall4         58 uspace/lib/c/include/libc.h 	__syscall4(p1, p2, p3, p4, 0, 0, id)
__syscall4         58 uspace/lib/posix/include/libc/libc.h 	__syscall4(p1, p2, p3, p4, 0, 0, id)
HelenOS homepage, sources at GitHub