sigaltstack(2)sigaltstack(2)NAMEsigaltstack - set and/or get signal alternate stack context.
The function allows a process to define and examine the state of an
alternate stack for signal handlers. Signals that have been explicitly
declared to execute on the alternate stack will be delivered on the
If ss is not a null pointer, it points to a structure that specifies
the alternate signal stack that will take effect upon return from The
ss_flags member specifies the new stack state. If it is set to the
stack is disabled and ss_sp and ss_size are ignored. Otherwise the
stack will be enabled, and the ss_sp and ss_size members specify the
new address and size of the stack.
The range of addresses starting at ss_sp, up to but not including
ss_sp+ss_size, is available to the implementation for use as the
stack. This interface makes no assumptions regarding which end is the
stack base and in which direction the stack grows as items are pushed.
If oss is not a null pointer, on successful completion it will point to
a structure that specifies the alternate signal stack that was in
effect prior to the call to The ss_sp and ss_size members specify the
address and size of that stack. The ss_flags member specifies the
stack's state, and may contain one of the following values:
SS_ONSTACK The process is currently executing on
the alternate signal stack. Attempts
to modify the alternate signal stack
while the process is executing on it
fails. This flag must not be modified
SS_DISABLE The alternate signal stack is currently
The value is a system default specifying the number of bytes that would
be used to cover the usual case when manually allocating an alternate
stack area. The value 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 system
implementation overhead. The constants and are defined in
After a successful call to one of the functions, there are no alternate
signal stacks in the new process image.
Upon successful completion, returns 0. Otherwise, it returns −1 and
sets to indicate the error.
The function will fail if:
[EINVAL] The ss argument is not a null pointer,
and the ss_flags member pointed to by
ss contains flags other than
[ENOMEM] The size of the alternate stack area is
[EPERM] An attempt was made to modify an active
At HP-UX release 11i Version 1.6 and forward, use of in threads created
with process contention scope will result in undefined behavior. This
function will continue to be reliable in threads created with system
The following code fragment illustrates a method for allocating memory
for an alternate stack:
In some implementations, a signal (whether or not indicated to execute
on the alternate stack) will always execute on the alternate stack if
it is delivered while another signal is being caught using the alter‐
On some implementations, stack space is automatically extended as
needed. On those implementations, automatic extension is typically not
available for an alternate stack. If the stack overflows, the behavior
Each thread may define an alternate signal handling stack.
LWP (Light Weight Processes) Considerations
Each LWP may define an alternate signal handling stack.
SEE ALSOsigaction(2), setjmp(3C), <signal.h>.
First released in Issue 4, Version 2.