SIGALTSTACK(2)						     Linux Programmer's Manual						    SIGALTSTACK(2)

NAME

       sigaltstack - get or set alternate signal stack content

SYNOPSIS

       #include <signal.h>

       int sigaltstack(const stack_t *ss, stack_t *oss);

       where:

       ss     points to a signalstack structure defined in <signal.h> containing stack content after the call.

       oss    if not NULL, points to a signalstack structure containing stack content before the call.

DESCRIPTION

       sigaction(2)  may  indicate that a signal should execute on an alternate stack. Where this is the case, sigaltstack(2) stores the signal in
       an alternate stack structure ss where its execution status may be examined prior to processing.

       The sigaltstack struct is defined in <signal.h> as follows:

		  void	     *ss_sp	/* SVID3 uses caddr_t ss_sp
		  int	     ss_flags
		  size_t     ss_size
       where:

       ss_sp  points to the stack structure.

       ss_flags
	      specifies the stack state to SS_DISABLE or SS_ONSTACK as follows:

	      If ss is not NULL,the new state may be set to SS_DISABLE, which specifies that the stack is to be disabled and ss_sp and ss_size are
	      ignored.	If SS_DISABLE is not set, the stack will be enabled.

	      If  oss is not NULL, the stack state may be either SS_ONSTACK or SS_DISABLE. The value SS_ONSTACK indicates that the process is cur-
	      rently executing on the alternate stack and that any attempt to modify it during execution will fail.  The  value  SS_DISABLE  indi-
	      cates that the current signal stack is disabled.

       ss_size
	      specifies the size of the stack.

       The  value  SIGSTKSZ  defines  the average number of bytes used when allocating an alternate stack area.  The value MINSIGSTKSZ defines the
       minimum stack size for a signal handler.  When processing an alternate stack size, your program should include these values  in	the  stack
       requirement to plan for the overhead of the operating system.

RETURN VALUES

       sigaltstack(2) returns 0 on success and -1 on failure.

ERRORS

       sigaltstack(2) sets  errno for the following conditions:

       EINVAL ss is not a null pointer the ss_flags member pointed to by ss contains flags other than SS_DISABLE.

       ENOMEM The size of the alternate stack area is less than MINSIGSTKSZ.

       EPERM  An attempt was made to modify an active stack.

STANDARDS

       This function comforms to: XPG4-UNIX.

SEE ALSO

       getcontext(2), sigaction(2), sigsetjmp(3).

Red Hat Linux 6.1						 20 September 1999						    SIGALTSTACK(2)