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.\"     @(#)sigreturn.2	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: src/lib/libc/sys/sigreturn.2,v 1.18.10.1.6.1 2010/12/21 17:09:25 kensmith Exp $
.\"
.Dd June 4, 1993
.Dt SIGRETURN 2
.Os
.Sh NAME
.Nm sigreturn
.Nd return from signal
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In signal.h
.Ft int
.Fn sigreturn "const ucontext_t *scp"
.Sh DESCRIPTION
The
.Fn sigreturn
system call
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 structure pointed to by
.Fa scp .
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
.Xr longjmp 3
when returning from a signal to the previously executing program.
.Sh NOTES
This system call is not available in
.Bx 4.2
hence it should not be used if backward compatibility is needed.
.Sh RETURN VALUES
If successful, the system call does not return.
Otherwise, a value of -1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn sigreturn
system call
will fail and the process context will remain unchanged
if one of the following occurs.
.Bl -tag -width Er
.It Bq Er EFAULT
The
.Fa scp
argument
points to memory that is not a valid part of the process
address space.
.It Bq Er EINVAL
The process status longword is invalid or would improperly
raise the privilege level of the process.
.El
.Sh SEE ALSO
.Xr sigvec 2 ,
.Xr setjmp 3 ,
.Xr ucontext 3
.Sh HISTORY
The
.Fn sigreturn
system call appeared in
.Bx 4.3 .