sigaltstack

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> con-
	      taining 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 exam-
       ined 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	 fol-
	      lows:

	      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
	      currently executing on the alternate stack and that any attempt
	      to  modify it during execution will fail.	 The value SS_DISABLE
	      indicates 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 allo-
       cating  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)