Fix some groff warnings.
[dragonfly.git] / lib / libc / sys / tls.2
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1.\" Copyright (c) 2003,2004 The DragonFly Project. All rights reserved.
2.\"
3.\" This code is derived from software contributed to The DragonFly Project
4.\" by David Xu <davidxu@freebsd.org> and Matthew Dillon <dillon@backplane.com>
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cb65615c 33.\" $DragonFly: src/lib/libc/sys/tls.2,v 1.3 2005/03/08 20:29:55 swildner Exp $
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34.\"
35.Dd February 21, 2005
36.Dt TLS 2
37.Os
38.Sh NAME
39.Nm sys_set_tls_area ,
40.Nm sys_get_tls_area
41.Nd kernel TLS (thread local storage) support.
42.Sh LIBRARY
43.Lb libc
44.Sh SYNOPSIS
45.In sys/tls.h
46.Ft int
47.Fn sys_set_tls_area "int which" "struct tls_info *info" "int infosize"
48.Ft int
49.Fn sys_get_tls_area "int which" "struct tls_info *info" "int infosize"
50.Sh DESCRIPTION
51The
52.Fn sys_set_tls_area
53system call creates an entry for the TLS facility
54.Fa which
55representing thread local storage as specified by the
56.Fa info
57structure. A descriptor representing the facility is returned, or -1 if
58an error occured. The facility may be cleared by specifying a NULL pointer
59and an infosize of 0.
60The
61.Fn sys_get_tls_area
62system call retrieves the requested TLS facility. A descriptor representing
63the facility is returned, or -1 if an error occured. If you simply want the
64descriptor you may specify a NULL pointer and an infosize of 0.
65.Pp
66The returned descriptor and the TLS mechanism is machine-dependant. On IA32
67three global segment descriptors are supported (0, 1, and 2) and the %gs
68load value is returned.
69.Pp
70The
71.Fa tls_info
72structure passed to
73.Fn sys_set_tls_area
74should first be zerod (to remain compatible with future extensions)
75and then initialized.
76.Pp
77.Bd -literal
78struct tls_info {
79 void *base; /* base address of TLS area */
80 int size; /* size of TLS area in bytes */
81};
82.Ed
83.Pp
84The actual implementation of the area is machine-dependant. If the kernel
85is unable to accomodate the supplied size it may create a larger area.
86If the kernel is unable to accomodate the supplied base address an error
87will be returned.
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88.Sh RETURN VALUES
89A return value of 0 is returned on success, -1 on error.
90.Sh ERRORS
91.Bl -tag -width Er
92.It Bq Er ERANGE
93The specified facility index,
94.Fa which ,
95is not supported.
96.It Bq Er EINVAL
97An invalid parameter has been specified.
98.It Bq Er ENOENT
99(sys_get_tls_area) The specified facility has not been initialized with
100.Fn sys_set_tls_area .
720180cd 101.El
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102.Sh EXAMPLE
103.Bd -literal -compact
104
105/*
106 * Pseudo example showing how the TLS system calls work on IA32.
107 */
108#include <stdio.h>
109#include <unistd.h>
110#include <stdlib.h>
111#include <errno.h>
112#include <sys/tls.h>
113
114int X;
115
116static int getdata(int offset);
117
118int
119main(int ac, char **av)
120{
121 int i;
122 int gs;
123 struct tls_info info;
124
125 info.base = &X;
126 info.size = sizeof(X);
127 if ((gs = sys_set_tls_area(0, &info, sizeof(info))) < 0) {
128 perror("setarea");
129 exit(1);
130 }
131 printf("gs = %04x\n", gs);
132 __asm __volatile("movl %0,%%eax; movl %%eax,%%gs" : "=m" (gs) : : "ax");
133
134 if (sys_get_tls_area(0, &info, sizeof(info)) < 0) {
135 perror("getarea");
136 exit(1);
137 }
138 printf("%p/%d\n", info.base, info.size);
139
140 X = 1;
141 printf("should be 1: %d\n", getdata(0));
142 X = 2;
143 printf("should be 2: %d\n", getdata(0));
144
145 printf("this should fault:\n");
146 fflush(stdout);
147 getdata(4);
148
149 return(0);
150}
151
152static int
153getdata(int offset)
154{
155 int rv;
156 __asm __volatile("movl %%gs:(%0),%%eax; movl %%eax,%1" : "+r" (offset) : "m"
157 (rv) : "ax");
158 return (rv);
159}
160
161.Ed
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162.Sh SEE ALSO
163.Xr umtx 2
164.Sh HISTORY
165The
166.Fn sys_set_tls_area ,
167and
168.Fn sys_get_tls_area
169function calls first appeared in DragonFly 1.1 .