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10 .TH MAKECONTEXT 3C "Mar 8, 2004"
11 .SH NAME
12 makecontext, swapcontext \- manipulate user contexts
13 .SH SYNOPSIS
14 .LP
15 .nf
16 #include <ucontext.h>
17
18 \fBvoid\fR \fBmakecontext\fR(\fBucontext_t *\fR\fIucp\fR, \fBvoid (*\fR\fIfunc\fR)(), \fBint\fR \fIargc\fR...);
19 .fi
20
21 .LP
22 .nf
23 \fBint\fR \fBswapcontext\fR(\fBucontext_t *restrict\fR \fIoucp\fR,
24 \fBconst ucontext_t *restrict\fR \fIucp\fR);
25 .fi
26
27 .SH DESCRIPTION
28 .sp
29 .LP
30 The \fBmakecontext()\fR function modifies the context specified by \fIucp\fR,
31 which has been initialized using \fBgetcontext\fR(2). When this context is
32 resumed using \fBswapcontext()\fR or \fBsetcontext\fR(2), execution continues
33 by calling the function \fIfunc\fR, passing it the arguments that follow
34 \fIargc\fR in the \fBmakecontext()\fR call. The value of \fIargc\fR must match
35 the number of pointer-sized integer arguments passed to \fIfunc\fR, otherwise
36 the behavior is undefined.
37 .sp
38 .LP
39 Before a call is made to \fBmakecontext()\fR, the context being modified should
40 have a stack allocated for it. The stack is assigned to the context by
41 initializing the \fBuc_stack\fR member.
42 .sp
43 .LP
44 The \fBuc_link\fR member is used to determine the context that will be resumed
45 when the context being modified by \fBmakecontext()\fR returns. The
46 \fBuc_link\fR member should be initialized prior to the call to
47 \fBmakecontext()\fR. If the \fBuc_link\fR member is initialized to \fINULL\fR,
48 the thread executing \fIfunc\fR will exit when \fIfunc\fR returns. See
49 \fBpthread_exit\fR(3C).
50 .sp
51 .LP
52 The \fBswapcontext()\fR function saves the current context in the context
53 structure pointed to by \fIoucp\fR and sets the context to the context
54 structure pointed to by \fIucp\fR.
55 .sp
56 .LP
57 If the \fIucp\fR or \fIoucp\fR argument points to an invalid address, the
58 behavior is undefined and \fBerrno\fR may be set to \fBEFAULT\fR.
59 .SH RETURN VALUES
60 .sp
61 .LP
62 On successful completion, \fBswapcontext()\fR returns \fB0\fR. Otherwise,
63 \fB\(mi1\fR is returned and \fBerrno\fR is set to indicate the error.
64 .SH ERRORS
65 .sp
66 .LP
67 The \fBswapcontext()\fR function will fail if:
68 .sp
69 .ne 2
70 .na
71 \fB\fBENOMEM\fR\fR
72 .ad
73 .RS 10n
74 The \fIucp\fR argument does not have enough stack left to complete the
75 operation.
76 .RE
77
78 .sp
79 .LP
80 The \fBswapcontext()\fR function may fail if:
81 .sp
82 .ne 2
83 .na
84 \fB\fBEFAULT\fR\fR
85 .ad
86 .RS 10n
87 The \fIucp\fR or \fIoucp\fR argument points to an invalid address.
88 .RE
89
90 .SH EXAMPLES
91 .LP
92 \fBExample 1 \fRAlternate execution context on a stack whose memory was
93 allocated using \fBmmap()\fR.
94 .sp
95 .in +2
96 .nf
97 #include <stdio.h>
98 #include <ucontext.h>
99 #include <sys/mman.h>
100
101 void
102 assign(long a, int *b)
103 {
104 *b = (int)a;
105 }
106
107 int
108 main(int argc, char **argv)
109 {
110 ucontext_t uc, back;
111 size_t sz = 0x10000;
112 int value = 0;
113
114 getcontext(&uc);
115
116 uc.uc_stack.ss_sp = mmap(0, sz,
117 PROT_READ | PROT_WRITE | PROT_EXEC,
118 MAP_PRIVATE | MAP_ANON, -1, 0);
119 uc.uc_stack.ss_size = sz;
120 uc.uc_stack.ss_flags = 0;
121
122 uc.uc_link = &back;
123
124 makecontext(&uc, assign, 2, 100L, &value);
125 swapcontext(&back, &uc);
126
127 printf("done %d\en", value);
128
129 return (0);
130 }
131 .fi
132 .in -2
133
134 .SH USAGE
135 .sp
136 .LP
137 These functions are useful for implementing user-level context switching
138 between multiple threads of control within a process (co-processing). More
139 effective multiple threads of control can be obtained by using native support
140 for multithreading. See \fBthreads\fR(5).
141 .SH ATTRIBUTES
142 .sp
143 .LP
144 See \fBattributes\fR(5) for descriptions of the following attributes:
145 .sp
146
147 .sp
148 .TS
149 box;
150 c | c
151 l | l .
152 ATTRIBUTE TYPE ATTRIBUTE VALUE
153 _
154 Interface Stability Standard
155 _
156 MT-Level MT-Safe
157 .TE
158
159 .SH SEE ALSO
160 .sp
161 .LP
162 \fBmmap\fR(2), \fBgetcontext\fR(2), \fBsigaction\fR(2), \fBsigprocmask\fR(2),
163 \fBpthread_exit\fR(3C), \fBucontext.h\fR(3HEAD), \fBattributes\fR(5),
164 \fBstandards\fR(5), \fBthreads\fR(5)
165 .SH NOTES
166 .sp
167 .LP
168 The semantics of the \fBuc_stack\fR member of the \fBucontext_t\fR structure
169 have changed as they apply to inputs to \fBmakecontext()\fR. Prior to Solaris
170 10, the \fBss_sp\fR member of the \fBuc_stack\fR structure represented the high
171 memory address of the area reserved for the stack. The \fBss_sp\fR member now
172 represents the base (low memory address), in keeping with other uses of
173 \fBss_sp\fR.
174 .sp
175 .LP
176 This change in the meaning of \fBss_sp\fR is now the default behavior. The
177 \fB-D__MAKECONTEXT_V2_SOURCE\fR compilation flag used in Solaris 9 update
178 releases to access this behavior is obsolete.
179 .sp
180 .LP
181 Binary compatibility has been preserved with releases prior to Solaris 10.
182 Before recompiling, applications that use \fBmakecontext()\fR must be updated
183 to reflect this behavior change. The example below demonstates a typical change
184 that must be applied:
185 .sp
186 .in +2
187 .nf
188 --- example1_s9.c Thu Oct 3 11:58:17 2002
189 +++ example1.c Thu Jun 27 13:28:16 2002
190 @@ -27,12 +27,9 @@
191 uc.uc_stack.ss_sp = mmap(0, sz,
192 PROT_READ | PROT_WRITE | PROT_EXEC,
193 MAP_PRIVATE | MAP_ANON, -1, 0);
194 - uc.uc_stack.ss_sp = (char *)uc.uc_stack.ss_sp + sz - 8;
195 uc.uc_stack.ss_size = sz;
196 uc.uc_stack.ss_flags = 0;
197
198 uc.uc_link = &back
199
200 makecontext(&uc, assign, 2, 100L, &value);
201 .fi
202 .in -2
203