1.\" $OpenBSD: i386_get_gsbase.2,v 1.5 2016/03/30 06:58:06 jmc Exp $ 2.\" $NetBSD: i386_get_ioperm.2,v 1.3 1996/02/27 22:57:17 jtc Exp $ 3.\" 4.\" Copyright (c) 1996 The NetBSD Foundation, Inc. 5.\" All rights reserved. 6.\" 7.\" This code is derived from software contributed to The NetBSD Foundation 8.\" by John T. Kohl and Charles M. Hannum. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE 23.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29.\" POSSIBILITY OF SUCH DAMAGE. 30.\" 31.Dd $Mdocdate: March 30 2016 $ 32.Dt I386_GET_GSBASE 2 i386 33.Os 34.Sh NAME 35.Nm i386_get_gsbase , 36.Nm i386_set_gsbase 37.Nd manage i386 per-thread %gs base address 38.Sh SYNOPSIS 39.In sys/types.h 40.In machine/sysarch.h 41.Ft int 42.Fn i386_get_gsbase "void **base" 43.Ft int 44.Fn i386_set_gsbase "void *base" 45.Sh DESCRIPTION 46.Fn i386_get_gsbase 47copies the current base address of the segment that, by default, 48is referenced by the %gs selector into the memory referenced by 49.Fa base . 50.Pp 51.Fn i386_set_gsbase 52sets the base address of the segment that, by default, is referenced 53by %gs to the address 54.Fa base . 55.Pp 56The segment base address is local to each thread. 57The initial thread of a new process inherits its segment base address 58from the parent thread. 59.Xr __tfork 3 60sets the initial segment base address for threads that it creates. 61.Pp 62.Sy Note: 63Code using the 64.Fn i386_get_gsbase 65and 66.Fn i386_set_gsbase 67functions must be compiled using 68.Cm -li386 . 69.Sh RETURN VALUES 70Upon successful completion, 71.Fn i386_get_gsbase 72and 73.Fn i386_set_gsbase 74return 0. 75Otherwise, a value of \-1 is returned and the global variable 76.Va errno 77is set to indicate the error. 78.Sh ERRORS 79.Fn i386_get_gsbase 80will fail if: 81.Bl -tag -width [EINVAL] 82.It Bq Er EFAULT 83.Fa base 84points outside the process's allocated address space. 85.El 86.Sh SEE ALSO 87.Xr fork 2 , 88.Xr __tfork 3 89.Rs 90.%A Intel 91.%T i386 Microprocessor Programmer's Reference Manual 92.Re 93.Sh WARNING 94The ELF Thread-Local Storage ABI reserves %gs for its own use and 95requires that the dynamic linker and thread library set it to 96reference data-structures internal to and shared between them. 97Programs should use the __thread storage class keyword instead of 98using these calls. 99To be maximally portable, 100programs that require per-thread data should use the 101.Fn pthread_key_create 102interface. 103