sigstack(3ucb) [opensolaris man page]

sigstack(3UCB)					     SunOS/BSD Compatibility Library Functions					    sigstack(3UCB)

NAME

       sigstack - set and/or get signal stack context

SYNOPSIS

       /usr/ucb/cc [ flag ... ] file ...
       #include <signal.h>

       int sigstack(nss, oss)
       struct sigstack *nss, *oss;

DESCRIPTION

       The sigstack() function allows users to define an alternate stack, called the "signal stack", on which signals are to be processed.  When a
       signal's action indicates its handler should execute on the signal stack (specified with a sigvec(3UCB) call), the system checks to see	if
       the  process  is  currently  executing on that stack.  If the process is not currently executing on the signal stack, the system arranges a
       switch to the signal stack for the duration of the signal handler's execution.

       A signal stack is specified by a sigstack() structure, which includes the following members:

	 char  *ss_sp;	      /* signal stack pointer */
	 int   ss_onstack;    /* current status */

       The ss_sp member is the initial value to be assigned to the stack pointer when the system switches the process to the  signal  stack.  Note
       that,  on  machines  where  the	stack  grows  downwards in memory, this is not the address of the beginning of the signal stack area.  The
       ss_onstack member is zero or non-zero depending on whether the process is currently executing on the signal stack or not.

       If nss is not a null pointer, sigstack() sets the signal stack state to the value in the sigstack() structure pointed to by nss. If nss	is
       a  null	pointer,  the signal stack state will be unchanged.  If oss is not a null pointer, the current signal stack state is stored in the
       sigstack() structure pointed to by oss.

RETURN VALUES

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

ERRORS

       The sigstack() function will fail and the signal stack context will remain unchanged if one of the following occurs.

       EFAULT	 Either nss or oss points to memory that is not a valid part of the process address space.

SEE ALSO

       cc(1B), sigaltstack(2), sigvec(3UCB), signal(3C)

WARNINGS

       Signal stacks are not "grown" automatically, as is done for the normal stack.  If the stack overflows unpredictable results may occur.

NOTES

       Use of these interfaces should be restricted to only applications written on BSD platforms.  Use of these interfaces with any of the system
       libraries or in multi-threaded applications is unsupported.

SunOS 5.11							    30 Oct 2007 						    sigstack(3UCB)

SIGALTSTACK(2)						      BSD System Calls Manual						    SIGALTSTACK(2)

NAME

     sigaltstack -- set and/or get signal stack context

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <signal.h>

     typedef struct sigaltstack {
	     void   *ss_sp;
	     size_t  ss_size;
	     int     ss_flags;
     } stack_t;

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

DESCRIPTION

     sigaltstack() allows users to define an alternative stack on which signals are to be processed.  If ss is non-zero, it specifies a pointer to
     and the size of a signal stack on which to deliver signals, and tells the system if the process is currently executing on that stack.  When a
     signal's action indicates its handler should execute on the signal stack (specified with a sigaction(2) call), the system checks to see if
     the process is currently executing on that stack.	If the process is not currently executing on the signal stack, the system arranges a
     switch to the signal stack for the duration of the signal handler's execution.

     If SS_DISABLE is set in ss_flags, ss_sp and ss_size are ignored and the signal stack will be disabled.  Trying to disable an active stack
     will cause sigaltstack to return -1 with errno set to EINVAL.  A disabled stack will cause all signals to be taken on the regular user stack.
     If the stack is later re-enabled then all signals that were specified to be processed on an alternative stack will resume doing so.

     If oss is non-zero, the current signal stack state is returned.  The ss_flags field will contain the value SS_ONSTACK if the process is cur-
     rently on a signal stack and SS_DISABLE if the signal stack is currently disabled.

NOTES

     The value SIGSTKSZ is defined to be the number of bytes/chars that would be used to cover the usual case when allocating an alternative stack
     area.  The following code fragment is typically used to allocate an alternative stack.

	   if ((sigstk.ss_sp = malloc(SIGSTKSZ)) == NULL)
		   /* error return */
	   sigstk.ss_size = SIGSTKSZ;
	   sigstk.ss_flags = 0;
	   if (sigaltstack(&sigstk,0) < 0)
		   perror("sigaltstack");

     An alternative approach is provided for programs with signal handlers that require a specific amount of stack space other than the default
     size.  The value MINSIGSTKSZ is defined to be the number of bytes/chars that is required by the operating system to implement the alternative
     stack feature.  In computing an alternative stack size, programs should add MINSIGSTKSZ to their stack requirements to allow for the operat-
     ing system overhead.

     Signal stacks are automatically adjusted for the direction of stack growth and alignment requirements.  Signal stacks may or may not be pro-
     tected by the hardware and are not ``grown'' automatically as is done for the normal stack.  If the stack overflows and this space is not
     protected unpredictable results may occur.

RETURN VALUES

     Upon successful completion, a value of 0 is returned.  Otherwise, a value of -1 is returned and errno is set to indicate the error.

ERRORS

     sigaltstack() will fail and the signal stack context will remain unchanged if one of the following occurs.

     [EFAULT]		Either ss or oss points to memory that is not a valid part of the process address space.

     [EINVAL]		An attempt was made to disable an active stack.

     [ENOMEM]		Size of alternative stack area is less than MINSIGSTKSZ.

SEE ALSO

     sigaction(2), setjmp(3), signal(7)

STANDARDS

     The sigaltstack() function conforms to X/Open Portability Guide Issue 4, Version 2 (``XPG4.2'').

HISTORY

     The predecessor to sigaltstack, the sigstack() system call, appeared in 4.2BSD.

CAVEATS

     Due to limitations in the current pthread implementation, sigaltstack should not be used in programs which link against the pthread(3)
     library (whether threads are used or not).

BSD
								  April 16, 2009							       BSD