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OpenSolaris 2009.06 - man page for sigaltstack (opensolaris section 2)

sigaltstack(2)				   System Calls 			   sigaltstack(2)

NAME
       sigaltstack - set or get signal alternate stack context

SYNOPSIS
       #include <signal.h>

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

DESCRIPTION
       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  cur-
       rently  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 sigaltstack(). 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:

       SS_DISABLE    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, 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 following values:

       SS_ONSTACK    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.

       SS_DISABLE    The alternate signal stack is currently disabled.

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

ERRORS
       The sigaltstack() function will fail if:

       EFAULT	 The ss or oss argument points to an illegal address.

       EINVAL	 The ss argument is not a null pointer, and 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.

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

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Async-Signal-Safe 	   |
       +-----------------------------+-----------------------------+

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

NOTES
       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 operating  sys-
       tem overhead.

       The following code fragment is typically used to allocate an alternate stack with an adja-
       cent 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)
		 perror("sigaltstack");

SunOS 5.11				    1 Nov 2003				   sigaltstack(2)


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