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SIGALTSTACK
Section: POSIX Programmer's Manual (3P)
Updated: 2003
Index
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PROLOG
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
sigaltstack - set and get signal alternate stack context
SYNOPSIS
#include <signal.h>
int sigaltstack(const stack_t *restrict ss, stack_t *restrict
oss);
DESCRIPTION
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, 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
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
Upon successful completion, sigaltstack() shall return 0; otherwise,
it shall return -1 and set errno to indicate
the error.
ERRORS
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.
EXAMPLES
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");
APPLICATION USAGE
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
None.
FUTURE DIRECTIONS
None.
SEE ALSO
Signal Concepts, sigaction(), sigsetjmp(), the
Base Definitions volume of IEEE Std 1003.1-2001, <signal.h>
COPYRIGHT
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 .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- Allocating Memory for an Alternate Stack
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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