opendarwin man page for __syscall

SYSCALL(2)						      BSD System Calls Manual							SYSCALL(2)

NAME
     syscall, __syscall -- indirect system call

SYNOPSIS
     #include <sys/syscall.h>
     #include <unistd.h>

     int
     syscall(int number, ...);

     int
     __syscall(quad_t number, ...);

DESCRIPTION
     Syscall() performs the system call whose assembly language interface has the specified number with the specified arguments.  Symbolic con-
     stants for system calls can be found in the header file <sys/syscall.h>.  The __syscall form should be used when one or more of the parame-
     ters is a 64-bit argument to ensure that argument alignment is correct.  This system call is useful for testing new system calls that do not
     have entries in the C library.

RETURN VALUES
     The return values are defined by the system call being invoked.  In general, a 0 return value indicates success.  A -1 return value indicates
     an error, and an error code is stored in errno.

BUGS
     There is no way to simulate system calls that have multiple return values such as pipe(2).

HISTORY
     The syscall() function call appeared in 4.0BSD.

4th Berkeley Distribution					   June 16, 1993					 4th Berkeley Distribution