xfree86 man page for syscall

syscall(3UCB)					     SunOS/BSD Compatibility Library Functions					     syscall(3UCB)

NAME
       syscall - indirect system call

SYNOPSIS
       /usr/ucb/cc [ flag ... ] file ...
       #include <sys/syscall.h>

       int syscall(number,  arg,  ...);

DESCRIPTION
       syscall()  performs the function whose assembly language interface has the specified number, and arguments arg ....  Symbolic constants for
       functions can be found in the header <sys/syscall.h>.

RETURN VALUES
       On error syscall() returns -1 and sets the external variable errno (see intro(2)).

FILES
       <sys/syscall.h>

SEE ALSO
       intro(2), pipe(2)

NOTES
       Use of these interfaces should be restricted to only applications written on BSD platforms.  Use of these interfaces with any of the system
       libraries or in multi-thread applications is unsupported.

WARNINGS
       There is no way to use syscall() to call functions such as pipe(2) which return values that do not fit into one hardware register.

       Since  many  system  calls  are	implemented  as library wrappers around traps to the kernel, these calls may not behave as documented when
       called from syscall(), which bypasses these wrappers. For these reasons, using syscall() is not recommended.

SunOS 5.10							    22 Jan 1993 						     syscall(3UCB)