144 lines
4.2 KiB
Groff
144 lines
4.2 KiB
Groff
.\" Copyright (c) 1980, 1991 Regents of the University of California.
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.\" 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. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. 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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.\" from: @(#)fork.2 6.5 (Berkeley) 3/10/91
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.\" $FreeBSD$
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.\"
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.Dd September 20, 1993
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.Dt I386_GET_LDT 2
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.Os
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.Sh NAME
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.Nm i386_get_ldt ,
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.Nm i386_set_ldt
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.Nd manage i386 per-process Local Descriptor Table entries
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In machine/segments.h
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.In machine/sysarch.h
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.Ft int
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.Fn i386_get_ldt "int start_sel" "union descriptor *descs" "int num_sels"
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.Ft int
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.Fn i386_set_ldt "int start_sel" "union descriptor *descs" "int num_sels"
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.Sh DESCRIPTION
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The
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.Fn i386_get_ldt
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system call
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will return the list of i386 descriptors that the process has in its
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LDT.
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The
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.Fn i386_set_ldt
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system call
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will set a list of i386 descriptors for the current process in its
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LDT.
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Both routines accept a starting selector number
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.Fa start_sel ,
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an array of memory that
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will contain the descriptors to be set or returned
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.Fa descs ,
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and the number of entries to set or return
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.Fa num_sels .
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.Pp
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The argument
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.Fa descs
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can be either segment_descriptor or gate_descriptor and are defined in
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.In i386/segments.h .
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These structures are defined by the architecture
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as disjoint bit-fields, so care must be taken in constructing them.
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.Pp
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If
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.Fa start_sel
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is
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.Em LDT_AUTO_ALLOC ,
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.Fa num_sels
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is 1 and the descriptor pointed to by
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.Fa descs
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is legal, then
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.Fn i386_set_ldt
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will allocate a descriptor and return its
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selector number.
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.Pp
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If
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.Fa num_descs
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is 1,
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.Fa start_sels
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is valid, and
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.Fa descs
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is NULL, then
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.Fn i386_set_ldt
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will free that descriptor
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(making it available to be reallocated again later).
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.Pp
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If
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.Fa num_descs
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is 0,
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.Fa start_sels
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is 0 and
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.Fa descs
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is NULL then, as a special case,
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.Fn i386_set_ldt
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will free all descriptors.
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.Sh RETURN VALUES
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Upon successful completion,
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.Fn i386_get_ldt
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returns the number of descriptors currently in the LDT.
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The
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.Fn i386_set_ldt
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system call
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returns the first selector set.
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In the case when a descriptor is allocated by the kernel, its number will
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be returned.
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Otherwise, a value of -1 is returned and the global
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variable
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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The
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.Fn i386_get_ldt
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and
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.Fn i386_set_ldt
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system calls
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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An inappropriate value was used for
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.Fa start_sel
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or
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.Fa num_sels .
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.It Bq Er EACCES
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The caller attempted to use a descriptor that would
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circumvent protection or cause a failure.
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.El
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.Sh SEE ALSO
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i386 Microprocessor Programmer's Reference Manual, Intel
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.Sh WARNING
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You can really hose your process using this.
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