Copyright (c) 1980 Regents of the University of California.
All rights reserved. The Berkeley software License Agreement
specifies the terms and conditions for redistribution.
@(#)syscall.2 4.1 (Berkeley) 05/09/85
All rights reserved. The Berkeley software License Agreement
specifies the terms and conditions for redistribution.
@(#)syscall.2 4.1 (Berkeley) 05/09/85
SYSCALL 2
C 4 NAME
syscall - indirect system call
SYNOPSIS
"syscall(number, r0, r1, arg ...)" (PDP-11) "syscall(number, arg, ...)" (VAX-11)
DESCRIPTION
Syscall performs the system call whose assembly language
interface has the specified
number, register arguments
r0 and
r1 (on the PDP-11, regardless of whether the entry point really
uses them) and further arguments
arg . The r0 value of the system call is returned.
DIAGNOSTICS
When the C-bit is set,
syscall returns -1 and sets the
external variable
errno (see
intro (2)). BUGS
There is no way to simulate system calls
such as
pipe (2), which return values in register r1.
"ASSEMBLER (PDP-11)"
(indir = 0.)
sys indir; call
The system call at the location call is executed. Execution resumes after the indir call.
On the PDP-11, the main purpose of indir is to allow a program to store arguments in system calls and execute them out of line in the data segment. This preserves the purity of the text segment.
If indir is executed indirectly, it is a no-op. If the instruction at the indirect location is not a system call, indir returns error code EINVAL; see intro (2).