1.\" $NetBSD: syscall.2,v 1.18 2009/08/07 19:34:46 dsl Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)syscall.2 8.1 (Berkeley) 6/16/93 31.\" 32.Dd August 7, 2009 33.Dt SYSCALL 2 34.Os 35.Sh NAME 36.Nm syscall , 37.Nm __syscall 38.Nd indirect system call 39.Sh LIBRARY 40.Lb libc 41.Sh SYNOPSIS 42.In sys/syscall.h 43.In unistd.h 44.Ft int 45.Fn syscall "int number" "..." 46.Ft quad_t 47.Fn __syscall "quad_t number" "..." 48.Sh DESCRIPTION 49.Fn syscall 50performs the system call whose assembly language 51interface has the specified 52.Fa number 53with the specified arguments. 54Symbolic constants for system calls can be found in the header file 55.Ao Pa sys/syscall.h Ac . 56The 57.Nm __syscall 58form should be used when one or more of the parameters is a 5964-bit argument to ensure that argument alignment is correct. 60.Pp 61This system call is useful for testing new system calls that 62do not have entries in the C library. 63It should not be used in normal applications. 64.Sh RETURN VALUES 65The return values are defined by the system call being invoked. 66In general, a 0 return value indicates success. 67A \-1 return value indicates an error, 68and an error code is stored in 69.Va errno . 70.Sh HISTORY 71The 72.Fn syscall 73function call appeared in 74.Bx 4.0 . 75.Sh BUGS 76There is no way to simulate system calls that have multiple return values 77such as 78.Xr pipe 2 . 79.Pp 80Since architectures return 32 bit and 64 bit results in different registers, 81it may be impossible to portably convert the result of 82.Fn __syscall 83to a 32bit value. 84For instance sparc returns 32 bit values in %o0 and 64 bit values in %o0:%o1 85(with %o0 containing the most significant part) so a 32 bit right shift 86of the result is needed to get a correct 32 bit result. 87.Pp 88Many architectures mask off the unwanted high bits of the syscall number, 89rather than returning an error. 90.Pp 91Due to ABI implementation differences in passing struct or union 92type arguments to system calls between different processors, all 93system calls pass instead pointers to such structs or unions, even 94when the documentation of the system call mentions otherwise. 95The conversion between passing structs and unions is handled normally 96via userland stubs. 97The correct arguments for the kernel entry 98points for each system call can be found in the header file 99.Ao Pa sys/syscallargs.h Ac 100