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.\" Copyright (c) 1985, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\"
.Dd March 11, 2026
.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 thread's signal mask and stack status are
restored from the context structure pointed to by
.Fa scp .
The system call does not return;
the whole userspace context as specified by
.Fa scp ,
including the userspace stack pointer, all general-purpose registers,
coprocessor state, process status register, and program counter
are restored from the context.
Execution resumes at the program counter from the specified context.
.Pp
This system call is used by the kernel-provided signal trampoline code,
located in the virtual DSO (VDSO) on some architectures or as raw code
in the shared page if VDSO is not provided,
when returning from a signal to the previously executing program.
.Sh RETURN VALUES
If successful, the system call does not return.
Otherwise, a value of -1 may be returned, with
.Va errno
set to indicate the error.
Some conditions detected by hardware result in the delivery of
a synchronous trap signal to the thread, in addition to or instead of
setting the system call error code.
.Sh ERRORS
The
.Fn sigreturn
system call
will fail and the thread 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 sigaction 2 ,
.Xr setjmp 3 ,
.Xr ucontext 3
.Sh HISTORY
The
.Fn sigreturn
system call appeared in
.Bx 4.3 .
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