1 .\" Copyright 2014 Garrett D'Amore <garrett@damore.org>
2 .\" Copyright 1989 AT&T. Copyright (c) 2004, Sun Microsystems, Inc. All Rights Reserved. Portions Copyright (c) 1992, X/Open Company Limited. All Rights Reserved.
3 .\" Sun Microsystems, Inc. gratefully acknowledges The Open Group for permission to reproduce portions of its copyrighted documentation. Original documentation from The Open Group can be obtained online at
4 .\" http://www.opengroup.org/bookstore/.
5 .\" The Institute of Electrical and Electronics Engineers and The Open Group, have given us permission to reprint portions of their documentation. In the following statement, the phrase "this text" refers to portions of the system documentation. Portions of this text are reprinted and reproduced in electronic form in the Sun OS Reference Manual, from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2004 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between these versions and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html.
6 .\" This notice shall appear on any product containing this material.
7 .\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License"). You may not use this file except in compliance with the License.
8 .\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing. See the License for the specific language governing permissions and limitations under the License.
9 .\" When distributing Covered Code, include this CDDL HEADER in each file and include the License file at usr/src/OPENSOLARIS.LICENSE. If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner]
10 .Dd "Jul 14, 2014"
11 .Dt MAKECONTEXT 3C
12 .Os
13 .Sh NAME
14 .Nm makecontext, swapcontext
15 .Nd manipulate user contexts
16 .Sh SYNOPSIS
17 .In ucontext.h
18 .Ft void
19 .Fn makecontext "ucontext_t *ucp" "void \*(lp*func\*(rp\*(lp\*(rp, int argc, ..."
20 .Ft int
21 .Fn swapcontext "ucontext_t *restrict oucp" "const ucontext_t *restrict ucp"
22 .Sh DESCRIPTION
23 The
24 .Fn makecontext
25 function modifies the context specified by
26 .Fa ucp ,
27 which has been initialized using
28 .Xr getcontext 2 .
29 When this context is
30 resumed using
31 .Fn swapcontext
32 or
33 .Xr setcontext 2 ,
34 execution continues by calling the function
35 .Fa func ,
36 passing it the arguments that follow
37 .Fa argc
38 in the
39 .Fn makecontext
40 call. The value of
41 .Fa argc
42 must match the number of pointer-sized integer arguments passed to
43 .Fn func ,
44 otherwise the behavior is undefined.
45 .Lp
46 Before a call is made to
47 .Fn makecontext ,
48 the context being modified should
49 have a stack allocated for it. The stack is assigned to the context by
50 initializing the
51 .Fa uc_stack
52 member.
53 .Lp
54 The
55 .Fa uc_link
56 member is used to determine the context that will be resumed
57 when the context being modified by
58 .Fn makecontext
59 returns. The
60 .Fa uc_link
61 member should be initialized prior to the call to
62 .Fn makecontext .
63 If the
64 .Fa uc_link
65 member is initialized to
66 .Dv NULL ,
67 the thread executing
68 .Fa func
69 will exit when
70 .Fa func
71 returns. See
72 .Xr pthread_exit 3C .
73 .Lp
74 The
75 .Fn swapcontext
76 function saves the current context in the context
77 structure pointed to by
78 .Fa oucp
79 and sets the context to the context
80 structure pointed to by
81 .Fa ucp .
82 .Lp
83 If the
84 .Fa ucp
85 or
86 .Fa oucp
87 argument points to an invalid address, the
88 behavior is undefined and
89 .Va errno
90 may be set to
91 .Er EFAULT .
92 .Sh RETURN VALUES
93 .Rv -std swapcontext
94 .Sh EXAMPLES
95 .Ss Example 1
96 The following example illustrates execution context on a stack whose memory was
97 allocated using
98 .Xr mmap 2 :
99 .Bd -literal -offset indent
100 #include <stdio.h>
101 #include <ucontext.h>
102 #include <sys/mman.h>
103
104 void
105 assign(long a, int *b)
106 {
107 *b = (int)a;
108 }
109
110 int
111 main(int argc, char **argv)
112 {
113 ucontext_t uc, back;
114 size_t sz = 0x10000;
115 int value = 0;
116
117 getcontext(&uc);
118
119 uc.uc_stack.ss_sp = mmap(0, sz,
120 PROT_READ | PROT_WRITE | PROT_EXEC,
121 MAP_PRIVATE | MAP_ANON, -1, 0);
122 uc.uc_stack.ss_size = sz;
123 uc.uc_stack.ss_flags = 0;
124
125 uc.uc_link = &back;
126
127 makecontext(&uc, assign, 2, 100L, &value);
128 swapcontext(&back, &uc);
129
130 printf("done %d\en", value);
131
132 return (0);
133 }
134 .Ed
135 .Sh ERRORS
136 The
137 .Fn swapcontext
138 function will fail if:
139 .Bl -tag -width Er
140 .It Er ENOMEM
141 The
142 .Fa ucp
143 argument does not have enough stack left to complete the operation.
144 .El
145 .Lp
146 The
147 .Fn swapcontext
148 function may fail if:
149 .Bl -tag -width Er
150 .It Er EFAULT
151 The
152 .Fa ucp
153 or
154 .Fa oucp
155 argument points to an invalid address.
156 .El
157 .Sh USAGE
158 These functions are useful for implementing user-level context switching
159 between multiple threads of control within a process (co-processing). More
160 effective multiple threads of control can be obtained by using native support
161 for multithreading. See
162 .Xr pthreads 5 .
163 .Sh INTERFACE STABILITY
164 .Sy Obsolete Standard .
165 .Sh MT-LEVEL
166 .Sy MT-Safe .
167 .Sh SEE ALSO
168 .Xr mmap 2 ,
169 .Xr getcontext 2 ,
170 .Xr sigaction 2 ,
171 .Xr sigprocmask 2 ,
172 .Xr pthread_exit 3C ,
173 .Xr ucontext.h 3HEAD ,
174 .Xr standards 5 ,
175 .Xr pthreads 5
176 .Sh NOTES
177 The semantics of the
178 .Fa uc_stack
179 member of the
180 .Ft ucontext_t
181 structure have changed as they apply to inputs to
182 .Fn makecontex .
183 Prior to Solaris 10, the
184 .Fa ss_sp
185 member of the
186 .Fa uc_stack
187 structure represented the high
188 memory address of the area reserved for the stack. The \fBss_sp\fR member now
189 represents the base (low memory address), in keeping with other uses of
190 .Fa ss_sp .
191 .Lp
192 This change in the meaning of
193 .Fa ss_sp
194 is now the default behavior. The
195 .Dv -D__MAKECONTEXT_V2_SOURCE
196 compilation flag used in Solaris 9 update
197 releases to access this behavior is obsolete.
198 .Lp
199 Binary compatibility has been preserved with releases prior to Solaris 10.
200 Before recompiling, applications that use
201 .Fn makecontext
202 must be updated
203 to reflect this behavior change.
204 .Lp
205 Portable applications should not use this function. Instead, applications
206 should use
207 .Xr pthreads 5
208 routines.
209 .Lp
210 Note that the definition of
211 .Fn makecontext
212 violates
213 .St -isoC .
214 There is no way to declare this function that does not violate that
215 standard.
216 .Sh STANDARDS
217 This function was introduced in
218 .St -xpg4.2 ,
219 and subsequently removed from
220 .St -p1003.1-2008 .