Section: POSIX Programmer's Manual (3P)
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
--- set and get signal alternate stack context
int sigaltstack(const stack_t *restrict ss, stack_t *restrict oss);
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.
is not a null pointer, it points to a
structure that specifies the alternate signal stack that shall take
effect upon return from
member specifies the new stack state. If it is set to SS_DISABLE, the
stack is disabled and
are ignored. Otherwise, the stack shall be enabled, and the
members specify the new address and size of the stack.
The range of addresses starting at
up to but not including
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.
is not a null pointer, upon successful completion it shall point to a
structure that specifies the alternate signal stack that was in effect
prior to the call to
members specify the address and size of that stack. The
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
After a successful call to one of the
functions, there are no alternate signal stacks in the new process
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
Use of this function by library threads that are not bound to
kernel-scheduled entities results in undefined behavior.
Upon successful completion,
shall return 0; otherwise, it shall return -1 and set
to indicate the error.
function shall fail if:
argument is not a null pointer, and the
member pointed to by
contains flags other than SS_DISABLE.
The size of the alternate stack area is less than MINSIGSTKSZ.
An attempt was made to modify an active stack.
The following sections are informative.
Allocating Memory for an Alternate Stack
The following example illustrates a method for allocating memory for an
if ((sigstk.ss_sp = malloc(SIGSTKSZ)) == NULL)
/* Error return. */
sigstk.ss_size = SIGSTKSZ;
sigstk.ss_flags = 0;
if (sigaltstack(&sigstk,(stack_t *)0) < 0)
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.
, Signal Concepts,
The Base Definitions volume of POSIX.1-2008,
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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
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