looking for syscalls especifications

[Sdävtaker]

Hello.
I was wondering if there is any place where i can get the
specifications used to write the syscalls.
I was reading the syscalls.master and it only says the number and name
of the syscall, and only few are documented at man.
Any idea who could have that kind of documentation?
As example, what determines the permitions of a just created file?
(From experiments i got they 000) same with the otehr almost 5000
syscalls :-/
Thanks for any help.
Sdav