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 delivering 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 middle. 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
disable 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,
sigaltstack(2) is recommended over this function.

SEE ALSO

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

February 28, 1996 SIGSTACK(3C)