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   1 '\" te
   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 .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 
   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 .