1.\" Copyright (c) 1980, 1991 Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.Dd October 14, 2006 29.Dt I386_GET_LDT 2 30.Os 31.Sh NAME 32.Nm i386_get_ldt , 33.Nm i386_set_ldt 34.Nd manage i386 per-process Local Descriptor Table entries 35.Sh LIBRARY 36.Lb libc 37.Sh SYNOPSIS 38.In machine/segments.h 39.In machine/sysarch.h 40.Ft int 41.Fn i386_get_ldt "int start_sel" "union descriptor *descs" "int num_sels" 42.Ft int 43.Fn i386_set_ldt "int start_sel" "union descriptor *descs" "int num_sels" 44.Sh DESCRIPTION 45The 46.Fn i386_get_ldt 47system call 48returns a list of the i386 descriptors in the current process' 49LDT. 50The 51.Fn i386_set_ldt 52system call 53sets a list of i386 descriptors in the current process' 54LDT. 55For both routines, 56.Fa start_sel 57specifies the index of the selector in the LDT at which to begin and 58.Fa descs 59points to an array of 60.Fa num_sels 61descriptors to be set or returned. 62.Pp 63Each entry in the 64.Fa descs 65array can be either a segment_descriptor or gate_descriptor and are defined in 66.In i386/segments.h . 67These structures are defined by the architecture 68as disjoint bit-fields, so care must be taken in constructing them. 69.Pp 70If 71.Fa start_sel 72is 73.Em LDT_AUTO_ALLOC , 74.Fa num_sels 75is 1 and the descriptor pointed to by 76.Fa descs 77is legal, then 78.Fn i386_set_ldt 79will allocate a descriptor and return its 80selector number. 81.Pp 82If 83.Fa num_descs 84is 1, 85.Fa start_sels 86is valid, and 87.Fa descs 88is NULL, then 89.Fn i386_set_ldt 90will free that descriptor 91(making it available to be reallocated again later). 92.Pp 93If 94.Fa num_descs 95is 0, 96.Fa start_sels 97is 0 and 98.Fa descs 99is NULL then, as a special case, 100.Fn i386_set_ldt 101will free all descriptors. 102.Sh RETURN VALUES 103Upon successful completion, 104.Fn i386_get_ldt 105returns the number of descriptors currently in the LDT. 106The 107.Fn i386_set_ldt 108system call 109returns the first selector set on success. 110If the kernel allocated a descriptor in the LDT, 111the allocated index is returned. 112Otherwise, a value of -1 is returned and the global 113variable 114.Va errno 115is set to indicate the error. 116.Sh ERRORS 117The 118.Fn i386_get_ldt 119and 120.Fn i386_set_ldt 121system calls 122will fail if: 123.Bl -tag -width Er 124.It Bq Er EINVAL 125An inappropriate value was used for 126.Fa start_sel 127or 128.Fa num_sels . 129.It Bq Er EACCES 130The caller attempted to use a descriptor that would 131circumvent protection or cause a failure. 132.El 133.Sh SEE ALSO 134i386 Microprocessor Programmer's Reference Manual, Intel 135.Sh WARNING 136You can really hose your process using this. 137