sigaltstack man page on SmartOS

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       sigaltstack - set or get signal alternate stack context

       #include <signal.h>

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

       The  sigaltstack()  function  allows a thread to define and examine the
       state of an alternate stack area on which signals are processed. If  ss
       is  non-zero, it specifies a pointer to and the size of a stack area on
       which to deliver signals, and informs the system whether the thread  is
       currently  executing  on	 that stack.  When a signal's action indicates
       its handler should execute on the  alternate  signal  stack  (specified
       with  a sigaction(2) call), the system checks whether the thread chosen
       to execute the signal handler is currently executing on that stack.  If
       the  thread  is not currently executing on the signal stack, the system
       arranges a switch to the alternate signal stack for the duration of the
       signal handler's execution.

       The  stack_t structure includes the following members:

	 int   *ss_sp
	 long  ss_size
	 int   ss_flags

       If  ss  is  not NULL, it points to a structure specifying the alternate
       signal stack that will take effect upon successful return from  sigalt‐
       stack(). The ss_sp and ss_size members specify the new base and size of
       the stack, which is automatically adjusted for direction of growth  and
       alignment.   The	 ss_flags member specifies the new stack state and may
       be set to the following:

		     The stack is to be disabled and  ss_sp  and  ss_size  are
		     ignored.  If  SS_DISABLE  is  not	set, the stack will be

       If oss is not NULL, it points to a structure specifying	the  alternate
       signal stack that was in effect prior to the call to sigaltstack(). The
       ss_sp and ss_size members specify the base and size of that stack.  The
       ss_flags	 member	 specifies the stack's state, and may contain the fol‐
       lowing values:

		     The thread is currently executing on the alternate signal
		     stack.  Attempts  to  modify  the	alternate signal stack
		     while the thread is executing on it will fail.

		     The alternate signal stack is currently disabled.

       Upon successful completion, 0 is return. Otherwise, −1 is returned  and
       errno is set to indicate the error.

       The sigaltstack() function will fail if:

		 The ss or oss argument points to an illegal address.

		 The  ss argument is not a null pointer, and the ss_flags mem‐
		 ber pointed to by ss contains flags other than SS_DISABLE.

		 The size of the  alternate  stack  area  is  less  than  MIN‐

		 An attempt was made to modify an active stack.

       See attributes(5) for descriptions of the following attributes:

       │Interface Stability │ Standard		│
       │MT-Level	    │ Async-Signal-Safe │

       getcontext(2), mmap(2), sigaction(2), ucontext.h(3HEAD), attributes(5),

       The value SIGSTKSZ is defined to be the number of bytes that  would  be
       used  to cover the usual case when allocating an alternate  stack area.
       The value MINSIGSTKSZ is defined to be the minimum  stack  size	for  a
       signal  handler.	  In  computing	 an  alternate	stack  size, a program
       should add that amount to its stack requirements to allow for the oper‐
       ating system overhead.

       The  following code fragment is typically used to allocate an alternate
       stack with an adjacent red zone (an unmapped  page)  to	guard  against
       stack overflow, as with default stacks:

	 #include <signal.h>
	 #include <sys/mman.h>

	 stack_t sigstk;
	 sigstk.ss_sp = mmap(NULL, SIGSTKSZ, PROT_READ | PROT_WRITE,
		 MAP_PRIVATE | MAP_ANON, -1, 0);
	 if (sigstk.ss_sp == MAP_FAILED)
		 /* error return */;
	 sigstk.ss_size = SIGSTKSZ;
	 sigstk.ss_flags = 0;
	 if (sigaltstack(&sigstk, NULL) < 0)

				  Nov 1, 2003			SIGALTSTACK(2)

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