sigstack - set and/or get alternate signal stack context
int sigstack(struct sigstack *ss, struct sigstack *oss);
The sigstack() function allows the calling process to indi-
cate 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 sig-
nal 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 sig-
nal 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 argu-
ment 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 sigac-
tion(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 sys-
tem 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.
Upon successful completion, sigstack() returns 0. Other-
wise, it returns -1 and sets errno to indicate the error.
The sigstack() function will fail if:
EPERM An attempt was made to modify an active stack.
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 his-
torical definition of struct sigstack. The only way to port-
ably 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
Applications should not use longjmp(3C) to leave a signal
handler that is running on a stack established with sig-
stack(). 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
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
fork(2), _longjmp(3C), longjmp(3C), setjmp(3C),
sigaltstack(2), siglongjmp(3C), sigsetjmp(3C)
Man(1) output converted with