4.3BSD/usr/man/man2/sigreturn.2

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.\" Copyright (c) 1985 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)sigreturn.2	6.2 (Berkeley) 6/30/85
.\"
.TH SIGRETURN 2 "June 30, 1985"
.UC 6
.SH NAME
sigreturn \- return from signal
.SH SYNOPSIS
.nf
.B #include <signal.h>
.PP
.B struct	sigcontext {
.B 	int	sc_onstack;
.B 	int	sc_mask;
.B 	int	sc_sp;
.B 	int	sc_fp;
.B 	int	sc_ap;
.B 	int	sc_pc;
.B 	int	sc_ps;
.B };
.PP
.B sigreturn(scp);
.B struct sigcontext *scp;
.SH DESCRIPTION
.I Sigreturn
allows users to atomically unmask, switch stacks,
and return from a signal context.
The processes signal mask and stack status are
restored from the context.
The system call does not return;
the users stack pointer, frame pointer, argument pointer,
and processor status longword are restored from the context.
Execution resumes at the specified pc.
This system call is used by the trampoline code, and
.IR longjmp (3)
when returning from a signal to the previously executing program.
.SH NOTES
This system call is not available in 4.2BSD,
hence it should not be used if backward compatibility is needed.
.SH "RETURN VALUE
If successful, the system call does not return.
Otherwise, a value of \-1 is returned and 
.I errno
is set to indicate the error.
.SH ERRORS
.I Sigreturn
will fail and the process context will remain unchanged
if one of the following occurs.
.TP 15
[EFAULT]
.I Scp
points to memory that is not a valid part of the process
address space.
.TP
[EINVAL]
The process status longword is invalid or would improperly
raise the privilege level of the process.
.SH "SEE ALSO"
sigvec(2), setjmp(3)