1.\" Copyright (c) 1985, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.Dd March 11, 2026 29.Dt SIGRETURN 2 30.Os 31.Sh NAME 32.Nm sigreturn 33.Nd return from signal 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.In signal.h 38.Ft int 39.Fn sigreturn "const ucontext_t *scp" 40.Sh DESCRIPTION 41The 42.Fn sigreturn 43system call 44allows users to atomically unmask, switch stacks, 45and return from a signal context. 46The thread's signal mask and stack status are 47restored from the context structure pointed to by 48.Fa scp . 49The system call does not return; 50the whole userspace context as specified by 51.Fa scp , 52including the userspace stack pointer, all general-purpose registers, 53coprocessor state, process status register, and program counter 54are restored from the context. 55Execution resumes at the program counter from the specified context. 56.Pp 57This system call is used by the kernel-provided signal trampoline code, 58located in the virtual DSO (VDSO) on some architectures or as raw code 59in the shared page if VDSO is not provided, 60when returning from a signal to the previously executing program. 61.Sh RETURN VALUES 62If successful, the system call does not return. 63Otherwise, a value of -1 may be returned, with 64.Va errno 65set to indicate the error. 66Some conditions detected by hardware result in the delivery of 67a synchronous trap signal to the thread, in addition to or instead of 68setting the system call error code. 69.Sh ERRORS 70The 71.Fn sigreturn 72system call 73will fail and the thread context will remain unchanged 74if one of the following occurs. 75.Bl -tag -width Er 76.It Bq Er EFAULT 77The 78.Fa scp 79argument 80points to memory that is not a valid part of the process 81address space. 82.It Bq Er EINVAL 83The process status longword is invalid or would improperly 84raise the privilege level of the process. 85.El 86.Sh SEE ALSO 87.Xr sigaction 2 , 88.Xr setjmp 3 , 89.Xr ucontext 3 90.Sh HISTORY 91The 92.Fn sigreturn 93system call appeared in 94.Bx 4.3 . 95