struct sigcontext {
             int sc_onstack;
             int sc_mask;
             int sc_sp;
             int sc_fp;
             int sc_ap;
             int sc_pc;
             int sc_ps;
     };

     int
     sigreturn(struct sigcontext *scp);

DESCRIPTION

     Sigreturn() 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.  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 speci-
     fied pc.  This system call is used by the trampoline code and longjmp(3)
     when returning from a signal to the previously executing program.

NOTES

     This system call is not available in 4.2 BSD hence it should not be used
     if backward compatibility is needed.

RETURN VALUES

     If successful, the system call does not return.  Otherwise, a value of -1
     is returned and errno is set to indicate the error.

ERRORS

     Sigreturn() will fail and the process context will remain unchanged if
     one of the following occurs.

     [EFAULT]           Scp 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)

HISTORY

     The sigreturn() function call appeared in 4.3BSD.

4.3 Berkeley Distribution        June 4, 1993        4.3 Berkeley Distribution