100 lines
3.8 KiB
Groff
100 lines
3.8 KiB
Groff
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.\" $NetBSD: syscall.2,v 1.18 2009/08/07 19:34:46 dsl Exp $
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.\"
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.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)syscall.2 8.1 (Berkeley) 6/16/93
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.\"
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.Dd August 7, 2009
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.Dt SYSCALL 2
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.Os
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.Sh NAME
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.Nm syscall ,
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.Nm __syscall
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.Nd indirect system call
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/syscall.h
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.In unistd.h
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.Ft int
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.Fn syscall "int number" "..."
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.Ft quad_t
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.Fn __syscall "quad_t number" "..."
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.Sh DESCRIPTION
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.Fn syscall
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performs the system call whose assembly language
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interface has the specified
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.Fa number
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with the specified arguments.
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Symbolic constants for system calls can be found in the header file
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.Ao Pa sys/syscall.h Ac .
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The
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.Nm __syscall
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form should be used when one or more of the parameters is a
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64-bit argument to ensure that argument alignment is correct.
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.Pp
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This system call is useful for testing new system calls that
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do not have entries in the C library.
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It should not be used in normal applications.
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.Sh RETURN VALUES
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The return values are defined by the system call being invoked.
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In general, a 0 return value indicates success.
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A \-1 return value indicates an error,
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and an error code is stored in
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.Va errno .
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.Sh HISTORY
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The
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.Fn syscall
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function call appeared in
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.Bx 4.0 .
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.Sh BUGS
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There is no way to simulate system calls that have multiple return values
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such as
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.Xr pipe 2 .
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.Pp
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Since architectures return 32 bit and 64 bit results in different registers,
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it may be impossible to portably convert the result of
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.Fn __syscall
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to a 32bit value.
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For instance sparc returns 32 bit values in %o0 and 64 bit values in %o0:%o1
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(with %o0 containing the most significant part) so a 32 bit right shift
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of the result is needed to get a correct 32 bit result.
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.Pp
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Many architectures mask off the unwanted high bits of the syscall number,
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rather than returning an error.
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.Pp
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Due to ABI implementation differences in passing struct or union
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type arguments to system calls between different processors, all
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system calls pass instead pointers to such structs or unions, even
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when the documentation of the system call mentions otherwise.
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The conversion between passing structs and unions is handled normally
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via userland stubs.
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The correct arguments for the kernel entry
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points for each system call can be found in the header file
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.Ao Pa sys/syscallargs.h Ac
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