1.\" Copyright (c) 2002 Packet Design, LLC. 2.\" All rights reserved. 3.\" 4.\" Subject to the following obligations and disclaimer of warranty, 5.\" use and redistribution of this software, in source or object code 6.\" forms, with or without modifications are expressly permitted by 7.\" Packet Design; provided, however, that: 8.\" 9.\" (i) Any and all reproductions of the source or object code 10.\" must include the copyright notice above and the following 11.\" disclaimer of warranties; and 12.\" (ii) No rights are granted, in any manner or form, to use 13.\" Packet Design trademarks, including the mark "PACKET DESIGN" 14.\" on advertising, endorsements, or otherwise except as such 15.\" appears in the above copyright notice or in the software. 16.\" 17.\" THIS SOFTWARE IS BEING PROVIDED BY PACKET DESIGN "AS IS", AND 18.\" TO THE MAXIMUM EXTENT PERMITTED BY LAW, PACKET DESIGN MAKES NO 19.\" REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING 20.\" THIS SOFTWARE, INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED 21.\" WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, 22.\" OR NON-INFRINGEMENT. PACKET DESIGN DOES NOT WARRANT, GUARANTEE, 23.\" OR MAKE ANY REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS 24.\" OF THE USE OF THIS SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, 25.\" RELIABILITY OR OTHERWISE. IN NO EVENT SHALL PACKET DESIGN BE 26.\" LIABLE FOR ANY DAMAGES RESULTING FROM OR ARISING OUT OF ANY USE 27.\" OF THIS SOFTWARE, INCLUDING WITHOUT LIMITATION, ANY DIRECT, 28.\" INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, PUNITIVE, OR CONSEQUENTIAL 29.\" DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES, LOSS OF 30.\" USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY THEORY OF 31.\" LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 32.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF 33.\" THE USE OF THIS SOFTWARE, EVEN IF PACKET DESIGN IS ADVISED OF 34.\" THE POSSIBILITY OF SUCH DAMAGE. 35.\" 36.\" $FreeBSD$ 37.\" 38.Dd March 23, 2020 39.Dt MAKECONTEXT 3 40.Os 41.Sh NAME 42.Nm makecontext , swapcontext 43.Nd modify and exchange user thread contexts 44.Sh LIBRARY 45.Lb libc 46.Sh SYNOPSIS 47.In ucontext.h 48.Ft void 49.Fo makecontext 50.Fa "ucontext_t *ucp" 51.Fa "void \*[lp]*func\*[rp]\*[lp]void\*[rp]" 52.Fa "int argc" ... 53.Fc 54.Ft int 55.Fn swapcontext "ucontext_t *oucp" "const ucontext_t *ucp" 56.Sh DESCRIPTION 57The 58.Fn makecontext 59function 60modifies the user thread context pointed to by 61.Fa ucp , 62which must have previously been initialized by a call to 63.Xr getcontext 3 64and had a stack allocated for it. 65The context is modified so that it will continue execution by invoking 66.Fn func 67with the arguments provided. 68The 69.Fa argc 70argument 71must be equal to the number of additional arguments of type 72.Vt int 73provided to 74.Fn makecontext 75and also equal to the number of arguments of type 76.Vt int 77to 78.Fn func ; 79otherwise , 80the behavior is undefined. 81.Pp 82The 83.Fa "ucp->uc_link" 84argument 85must be initialized before calling 86.Fn makecontext 87and determines the action to take when 88.Fn func 89returns: 90if equal to 91.Dv NULL , 92the process exits; 93otherwise, 94.Fn setcontext "ucp->uc_link" 95is implicitly invoked. 96.Pp 97The 98.Fn swapcontext 99function 100saves the current thread context in 101.Fa "*oucp" 102and makes 103.Fa "*ucp" 104the currently active context. 105.Sh RETURN VALUES 106If successful, 107.Fn swapcontext 108returns zero; 109otherwise \-1 is returned and the global variable 110.Va errno 111is set appropriately. 112.Sh ERRORS 113The 114.Fn swapcontext 115function 116will fail if: 117.Bl -tag -width Er 118.It Bq Er ENOMEM 119There is not enough stack space in 120.Fa ucp 121to complete the operation. 122.El 123.Sh SEE ALSO 124.Xr setcontext 3 , 125.Xr ucontext 3 126.Sh STANDARDS 127The 128.Fn makecontext 129and 130.Fn swapcontext 131functions conform to 132.St -xsh5 133and 134.St -p1003.1-2001 . 135.Pp 136The 137.St -p1003.1-2004 138revision marked the functions 139.Fn makecontext 140and 141.Fn swapcontext 142as obsolete, citing portability issues and recommending the use of 143.Tn POSIX 144threads instead. 145The 146.St -p1003.1-2008 147revision removed the functions from the specification. 148.Pp 149.Bf -symbolic 150The standard does not clearly define the type of integer arguments 151passed to 152.Fa func 153via 154.Fn makecontext ; 155portable applications should not rely on the implementation detail that 156it may be possible to pass pointer arguments to functions. 157.Sh HISTORY 158The 159.Fn makecontext 160and 161.Fn swapcontext 162functions first appeared in 163.At V.4 . 164