$home/manuals/unix_v8/2/syscall

SYSCALL(2)                    System Calls Manual                   SYSCALL(2)

NAME
       syscall - indirect system call

SYNOPSIS
       syscall(number, arg, ... )  (VAX)

       syscall(number, r0, r1, arg ... )  (PDP11)

DESCRIPTION
       Syscall  performs the system call whose assembly language interface has
       the specified number and arguments.

       On a PDP11 the first two arguments correspond to registers r0  and  r1,
       regardless of whether the entry point really uses them.

       The r0 value of the system call is returned.

DIAGNOSTICS
       When  the  C-bit is set, syscall returns -1 and sets the external vari‐
       able errno (see intro(2)).

BUGS
       There is no way to simulate system calls such as pipe(2), which  return
       values in register r1.

                                                                    SYSCALL(2)