List of and documentation for system calls for XNU kernel in OSX

Question

I'm trying to figure out how to get a list of and documentation for the system calls available in the XNU kernel in OSX. I've googled around quite a bit, but haven't been able to find anything of use. As I understand the calling conventions match BSD, is that correct?

Thanks

Answer 1

The "official" list is at Darwin page at Apple. Specifically, see the file syscalls.master in the XNU distribution. (If something you expect is missing, try a newer XNU version.)

The BSD part of the system calls comes from BSD, but there're mach calls which follow quite different conventions.

You'll definitely want to read Amit Singh's OS X kernel book, see the book's website. It's rewritten for 10.4 and mainly for PPC, but still is the greatest detailed info you can get on the kernel.

Answer 2

XNU's system calls are, indeed, following the BSD/POSIX model, but are a subset: There are quite a few additional calls proprietary to Apple - for example, stack_snapshot (#365), iopolicy (322), proc_info(336) and others. Apple keeps those undocumented, but you can find their source in XNU. You can call undocumented system calls explicitly (by using the sys call macro and specifying the call # as first argument), but some (e.g. proc_info) are wrapped by Darwin libraries (e.g. libproc, which is part of libSystem)

syscalls.master generates the /usr/include/sys/syscall.h file, which will also give you the system call names (but not the prototypes). Singh's book describes some sys calls, but is vastly outdated, since Tiger had fewer than the 439 (in iOS6: 443) calls XNU has today. A more recent book can be found in http://www.amazon.com/Mac-OS-iOS-Internals-Apples/dp/1118057651, and its appendix actually documents all system calls (and Mach Traps), in detail.