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.\" in the SunOS 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,
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.\" Copyright 1989 AT&T
.\" Portions Copyright (c) 1992, X/Open Company Limited. All Rights Reserved.
.\" Copyright (c) 2001, Sun Microsystems, Inc. All Rights Reserved.
.\" Copyright 2022 OmniOS Community Edition (OmniOSce) Association.
.\"
.Dd November 24, 2022
.Dt GETCONTEXT 2
.Os
.Sh NAME
.Nm getcontext ,
.Nm setcontext
.Nd get and set current user context
.Sh SYNOPSIS
.In ucontext.h
.Ft int
.Fo getcontext
.Fa "ucontext_t *ucp"
.Fc
.Ft int
.Fo setcontext
.Fa "const ucontext_t *ucp"
.Fc
.Sh DESCRIPTION
The
.Fn getcontext
function initializes the structure pointed to by
.Fa ucp
to the current user context of the calling process.
The
.Vt ucontext_t
type that
.Fa ucp
points to defines the user context and includes the contents of the calling
process' machine registers, the signal mask, and the current execution stack.
.Pp
The
.Fn setcontext
function restores the user context pointed to by
.Fa ucp .
A successful call to
.Fn setcontext
does not return; program execution resumes at the point specified by the
.Fa ucp
argument passed to
.Fn setcontext .
The
.Fa ucp
argument should be created either by a prior call to
.Fn getcontext ,
or by being passed as an argument to a signal handler.
If the
.Fa ucp
argument was created with
.Fn getcontext ,
program execution continues as if the corresponding call of
.Fn getcontext
had just returned.
If the
.Fa ucp
argument was created with
.Xr makecontext 3C ,
program execution continues with the function passed to
.Xr makecontext 3C .
When that function returns, the process continues as if after a call to
.Fn setcontext
with the
.Fa ucp
argument that was input to
.Xr makecontext 3C .
If the
.Fa ucp
argument was passed to a signal handler, program execution continues with the
program instruction following the instruction interrupted by the signal.
If the
.Fa uc_link
member of the
.Vt ucontext_t
structure pointed to by the
.Fa ucp
argument is
.Dv NULL ,
then this context is the main context, and the process
will exit when this context returns.
The effects of passing a
.Fa ucp
argument obtained from any other source are unspecified.
.Sh RETURN VALUES
On successful completion,
.Fn setcontext
does not return and
.Fn getcontext
returns 0.
Otherwise, -1 is returned.
.Sh ERRORS
No errors are defined.
.Sh USAGE
When a signal handler is executed, the current user context is saved and a new
context is created.
If the thread leaves the signal handler via
.Xr longjmp 3C ,
then it is unspecified whether the context at the time of the corresponding
.Xr setjmp 3C
call is restored and thus whether future calls to
.Fn getcontext
will provide an accurate representation of the current context, since the
context restored by
.Xr longjmp 3C
may not contain all the information that
.Fn setcontext
requires.
Signal handlers should use
.Xr siglongjmp 3C
instead.
.Pp
Portable applications should not modify or access the
.Fa uc_mcontext
member of
.Vt ucontext_t .
A portable application cannot assume that context includes any process-wide
static data, possibly including
.Va errno .
Users manipulating contexts should take care to handle these explicitly when
required.
.Sh INTERFACE STABILITY
.Sy Committed
.Sh SEE ALSO
.Xr sigaction 2 ,
.Xr sigaltstack 2 ,
.Xr sigprocmask 2 ,
.Xr bsd_signal 3C ,
.Xr makecontext 3C ,
.Xr setjmp 3C ,
.Xr sigsetjmp 3C ,
.Xr ucontext.h 3HEAD ,
.Xr attributes 7 ,
.Xr standards 7
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