SIGRETURN(2)							System Calls Manual						      SIGRETURN(2)

NAME

       sigreturn - return from signal

SYNOPSIS

       #include <signal.h>

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

       sigreturn(scp);
       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 specified 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 4.2BSD, hence it should not be used if backward compatibility is needed.

       The definition of the sigcontext structure is machine dependent (the structure cited above is that for a VAX running  4.3BSD);  no  program
       should depend on its internal structure.  Setjmp(3) may be used to build sigcontext structures in a machine independent manner.

RETURN VALUE

       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

       sigvec(2), setjmp(3)

NOTES  (PDP-11)
       On  the	PDP-11 the field sc_ap (argument pointer) does not exist and the field sc_fp (frame pointer) is the PDP-11 register r5.  Addition-
       ally, three new fields sc_r0, sc_r1 and sc_ovno are present on the PDP-11 which hold register values r0 and r1 and the text overlay  number
       to restore (see ld(1)).

       struct  sigcontext {
	       int   sc_onstack; /* sigstack state to restore */
	       long  sc_mask;	 /* signal mask to restore */
	       int   sc_sp;	 /* sp to restore */
	       int   sc_fp;	 /* fp to restore */
	       int   sc_r1;	 /* r1 to restore */
	       int   sc_r0;	 /* r0 to restore */
	       int   sc_pc;	 /* pc to restore */
	       int   sc_ps;	 /* psl to restore */
	       int   sc_ovno	 /* overlay to restore */
       };

4.3 Berkeley Distribution					   June 30, 1985						      SIGRETURN(2)