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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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SIGALTSTACK(3P) POSIX Programmer's Manual SIGALTSTACK(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.
sigaltstack — set and get signal alternate stack context
#include <signal.h>
int sigaltstack(const stack_t *restrict ss, stack_t *restrict oss);
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.
Upon successful completion, sigaltstack() shall return 0;
otherwise, it shall return -1 and set errno to indicate the error.
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
SS_DISABLE.
ENOMEM The size of the alternate stack area is less than
MINSIGSTKSZ.
EPERM 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 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)
perror("sigaltstack");
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.
None.
None.
Section 2.4, Signal Concepts, exec(1p), sigaction(3p),
sigsetjmp(3p)
The Base Definitions volume of POSIX.1‐2017, signal.h(0p)
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
http://www.opengroup.org/unix/online.html .
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
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 SIGALTSTACK(3P)
Pages that refer to this page: signal.h(0p), exec(3p), getrlimit(3p), sigaction(3p)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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