sigstack(3c) [opensolaris man page]

sigstack(3C)						   Standard C Library Functions 					      sigstack(3C)

NAME

       sigstack - set and/or get alternate signal stack context

SYNOPSIS

       #include <signal.h>

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

DESCRIPTION

       The sigstack() function allows the calling process to indicate to the system an area of its address space to be used for processing signals
       received by the process.

       If the ss argument is not a null pointer, it must point to a sigstack structure. The length of the application-supplied stack  must  be	at
       least SIGSTKSZ bytes. If the alternate signal stack overflows, the resulting behavior is undefined.  (See USAGE below.)

	   o	  The value of the ss_onstack member indicates whether the process wants the system to use an alternate signal stack when deliver-
		  ing signals.

	   o	  The value of the ss_sp member indicates the desired location of the alternate signal stack area in the process' address space.

	   o	  If the ss argument is a null pointer, the current alternate signal stack context is not changed.

       If the oss argument is not a null pointer, it points to a sigstack structure in which the current alternate signal stack context is placed.
       The  value stored in the ss_onstack member of oss will be non-zero if the process is currently executing on the alternate signal stack.	If
       the oss argument is a null pointer, the current alternate signal stack context is not returned.

       When a signal's action indicates its handler should execute on the alternate signal stack (specified by calling	sigaction(2)),	sigstack()
       checks  to  see	if  the  process  is currently executing on that stack.  If the process is not currently executing on the alternate signal
       stack, the system arranges a switch to the alternate signal stack for the duration of the signal handler's execution.

       After a successful call to one of the exec functions, there are no alternate signal stacks in the new process image.

RETURN VALUES

       Upon successful completion, sigstack() returns 0.  Otherwise, it returns -1 and sets errno to indicate the error.

ERRORS

       The sigstack() function will fail if:

       EPERM	An attempt was made to modify an active stack.

USAGE

       A portable application, when being written or rewritten, should use sigaltstack(2) instead of sigstack().

       The direction of stack growth is not indicated in the historical definition of struct sigstack. The only way to portably establish a  stack
       pointer is for the application to determine stack growth direction, or to allocate a block of storage and set the stack pointer to the mid-
       dle. sigstack() may assume that the size of the signal stack is SIGSTKSZ as found in <signal.h>. An application that would like to  specify
       a signal stack size other than SIGSTKSZ should use sigaltstack(2).

       Applications should not use longjmp(3C) to leave a signal handler that is running on a stack established with sigstack(). Doing so may dis-
       able future use of the signal stack.  For abnormal exit from a signal handler, siglongjmp(3C), setcontext(2),  or  swapcontext(3C)  may	be
       used. These functions fully support switching from one stack to another.

       The sigstack() function requires the application to have knowledge of the underlying system's stack architecture.  For this reason, sigalt-
       stack(2) is recommended over this function.

SEE ALSO

       fork(2), _longjmp(3C), longjmp(3C), setjmp(3C), sigaltstack(2), siglongjmp(3C), sigsetjmp(3C)

SunOS 5.11							    28 Feb 1996 						      sigstack(3C)

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

NAME

     sigaltstack -- set and/or get signal stack context

SYNOPSIS

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

     struct sigaltstack {
	     char   *ss_sp;
	     int     ss_size;
	     int     ss_flags;
     };

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

DESCRIPTION

     Sigaltstack() allows users to define an alternate 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 SA_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 alternate 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 SA_ONSTACK if the process is cur-
     rently on a signal stack and SA_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 alternate stack
     area.  The following code fragment is typically used to allocate an alternate 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 alternate
     stack feature.  In computing an alternate stack size, programs should add MINSIGSTKSZ to their stack requirements to allow for the operating
     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

     Sigstack() 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 alternate stack area is less than or equal to MINSIGSTKSZ.

SEE ALSO

     sigaction(2), setjmp(3)

HISTORY

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

4.2 Berkeley Distribution					   June 4, 1993 					 4.2 Berkeley Distribution