.\" Copyright (c) 1980, 1991 Regents of the University of California. .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" from: @(#)fork.2 6.5 (Berkeley) 3/10/91 .\" $FreeBSD: /repoman/r/ncvs/src/lib/libc/i386/sys/i386_get_ldt.2,v 1.21 2004/07/02 19:07:30 ru Exp $ .\" .Dd September 20, 1993 .Dt I386_GET_LDT 2 .Os .Sh NAME .Nm i386_get_ldt , .Nm i386_set_ldt .Nd manage i386 per-process Local Descriptor Table entries .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In architecture/i386/table.h .In i386/user_ldt.h .Ft int .Fn i386_get_ldt "int start_sel" "union ldt_entry *descs" "int num_sels" .Ft int .Fn i386_set_ldt "int start_sel" "union ldt_entry *descs" "int num_sels" .Sh DESCRIPTION The .Fn i386_get_ldt system call will return the list of i386 descriptors that the process has in its LDT. The .Fn i386_set_ldt system call will set a list of i386 descriptors for the current process in its LDT. Both routines accept a starting selector number .Fa start_sel , an array of memory that will contain the descriptors to be set or returned .Fa descs , and the number of entries to set or return .Fa num_sels . .Pp The argument .Fa descs can be either code_desc_t, data_desc_t or call_gate_t and are defined in .In architecture/i386/desc.h . These structures are defined by the architecture as disjoint bit-fields, so care must be taken in constructing them. .Pp If .Fa start_sel is .Em LDT_AUTO_ALLOC , .Fa num_sels is 1 and the descriptor pointed to by .Fa descs is legal, then .Fn i386_set_ldt will allocate a descriptor and return its selector number. .Pp If .Fa num_descs is 1, .Fa start_sels is valid, and .Fa descs is NULL, then .Fn i386_set_ldt will free that descriptor (making it available to be reallocated again later). .Pp If .Fa num_descs is 0, .Fa start_sels is 0 and .Fa descs is NULL then, as a special case, .Fn i386_set_ldt will free all descriptors. .Sh RETURN VALUES Upon successful completion, .Fn i386_get_ldt returns the number of descriptors currently in the LDT. The .Fn i386_set_ldt system call returns the first selector set. In the case when a descriptor is allocated by the kernel, its number will be returned. Otherwise, a value of -1 is returned and the global variable .Va errno is set to indicate the error. .Sh ERRORS The .Fn i386_get_ldt and .Fn i386_set_ldt system calls will fail if: .Bl -tag -width Er .It Bq Er EINVAL An inappropriate value was used for .Fa start_sel or .Fa num_sels . .It Bq Er EACCES The caller attempted to use a descriptor that would circumvent protection or cause a failure. .El .Sh SEE ALSO i386 Microprocessor Programmer's Reference Manual, Intel .Sh WARNING You can really hose your process using this.