sigaltstack(3p) — Linux manual page


SIGALTSTACK(3P)         POSIX Programmer's Manual        SIGALTSTACK(3P)

PROLOG         top

       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.

NAME         top

       sigaltstack — set and get signal alternate stack context

SYNOPSIS         top

       #include <signal.h>

       int sigaltstack(const stack_t *restrict ss, stack_t *restrict oss);

DESCRIPTION         top

       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 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 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, upon 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 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
                   fail. This flag shall not be modified by processes.

       SS_DISABLE  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.

RETURN VALUE         top

       Upon successful completion, sigaltstack() shall return 0;
       otherwise, it shall return -1 and set errno to indicate the

ERRORS         top

       The sigaltstack() function shall 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 less than

       EPERM  An attempt was made to modify an active stack.

       The following sections are informative.

EXAMPLES         top

   Allocating Memory for an Alternate Stack
       The following example illustrates a method for allocating memory
       for an alternate stack.

           #include <signal.h>
           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.

RATIONALE         top




SEE ALSO         top

       Section 2.4, Signal Concepts, exec(1p), sigaction(3p),

       The Base Definitions volume of POSIX.1‐2017, signal.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see .

IEEE/The Open Group               2017                   SIGALTSTACK(3P)

Pages that refer to this page: signal.h(0p)exec(3p)getrlimit(3p)sigaction(3p)