The sigaltstack() function allows a process to define and examine the
state of an alternate stack for signal handlers for the current thread.
Signals that have been explicitly declared to execute on the alternate stack
shall be delivered on the alternate stack.
If ss is not a null pointer, it points to a stack_t structure that
specifies the alternate signal stack that shall take effect upon return from
sigaltstack(). The ss_flags member specifies the new stack
state. If it is set to SS_DISABLE, the stack is disabled and ss_sp and
ss_size are ignored. Otherwise, the stack shall be enabled, and the
ss_sp and ss_size members specify the new address and size of
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 function 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 shall point to
a stack_t structure that specifies the alternate signal stack that was
in effect prior to the call to sigaltstack(). 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
The process is currently executing on the alternate signal
stack. Attempts to modify the alternate signal stack while the process is
executing on it fail. This flag shall not be modified by processes.
The alternate signal stack is currently disabled.
The value SIGSTKSZ 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 MINSIGSTKSZ 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 SS_ONSTACK, SS_DISABLE, SIGSTKSZ, and MINSIGSTKSZ are
defined in <signal.h>.
After a successful call to one of the exec functions, there are no
alternate signal stacks in the new process image.
In some implementations, a signal (whether or not indicated to execute on the
alternate stack) shall always execute on the alternate stack if it is
delivered while another signal is being caught using the alternate stack.
Use of this function by library threads that are not bound to kernel-scheduled
entities results in undefined behavior.
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 is undefined.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html