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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 .