SIGRETURN(2)              FreeBSD System Calls Manual             SIGRETURN(2)

NAME

     sigreturn - return from signal

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <signal.h>

     int
     sigreturn(const ucontext_t *scp);

DESCRIPTION

     The 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 scp.
     The system call does not return; the whole userspace context as specified
     by 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.

     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.

RETURN VALUES

     If successful, the system call does not return.  Otherwise, a value of -1
     may be returned, with 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.

ERRORS

     The sigreturn() system call will fail and the thread context will remain
     unchanged if one of the following occurs.

     [EFAULT]           The scp argument points to memory that is not a valid
                        part of the process address space.

     [EINVAL]           The process status longword is invalid or would
                        improperly raise the privilege level of the process.

SEE ALSO

     sigaction(2), setjmp(3), ucontext(3)

HISTORY

     The sigreturn() system call appeared in 4.3BSD.

FreeBSD 15.1-STABLE-HBSD        March 11, 2026                    SIGRETURN(2)