sigaltstack.3p (5528B)
- '\" et
- .TH SIGALTSTACK "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
- .\"
- .SH 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.
- .\"
- .SH NAME
- sigaltstack
- \(em set and get signal alternate stack context
- .SH SYNOPSIS
- .LP
- .nf
- #include <signal.h>
- .P
- int sigaltstack(const stack_t *restrict \fIss\fP, stack_t *restrict \fIoss\fP);
- .fi
- .SH DESCRIPTION
- The
- \fIsigaltstack\fR()
- 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.
- .P
- If
- .IR ss
- is not a null pointer, it points to a
- .BR stack_t
- structure that specifies the alternate signal stack that shall take
- effect upon return from
- \fIsigaltstack\fR().
- The
- .IR ss_flags
- member specifies the new stack state. If it is set to SS_DISABLE, the
- stack is disabled and
- .IR ss_sp
- and
- .IR ss_size
- are ignored. Otherwise, the stack shall be enabled, and the
- .IR ss_sp
- and
- .IR ss_size
- members specify the new address and size of the stack.
- .P
- The range of addresses starting at
- .IR ss_sp
- up to but not including
- .IR ss_sp +\c
- .IR 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.
- .P
- If
- .IR oss
- is not a null pointer, upon successful completion it shall point to a
- .BR stack_t
- structure that specifies the alternate signal stack that was in effect
- prior to the call to
- \fIsigaltstack\fR().
- The
- .IR ss_sp
- and
- .IR ss_size
- members specify the address and size of that stack. The
- .IR ss_flags
- member specifies the stack's state, and may contain one of the
- following values:
- .IP SS_ONSTACK 12
- 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.
- .IP SS_DISABLE 12
- The alternate signal stack is currently disabled.
- .P
- 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
- .IR <signal.h> .
- .P
- After a successful call to one of the
- .IR exec
- functions, there are no alternate signal stacks in the new process
- image.
- .P
- 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.
- .P
- Use of this function by library threads that are not bound to
- kernel-scheduled entities results in undefined behavior.
- .SH "RETURN VALUE"
- Upon successful completion,
- \fIsigaltstack\fR()
- shall return 0; otherwise, it shall return \-1 and set
- .IR errno
- to indicate the error.
- .SH ERRORS
- The
- \fIsigaltstack\fR()
- function shall fail if:
- .TP
- .BR EINVAL
- The
- .IR ss
- argument is not a null pointer, and the
- .IR ss_flags
- member pointed to by
- .IR ss
- contains flags other than SS_DISABLE.
- .TP
- .BR ENOMEM
- The size of the alternate stack area is less than MINSIGSTKSZ.
- .TP
- .BR EPERM
- An attempt was made to modify an active stack.
- .LP
- .IR "The following sections are informative."
- .SH EXAMPLES
- .SS "Allocating Memory for an Alternate Stack"
- .P
- The following example illustrates a method for allocating memory for an
- alternate stack.
- .sp
- .RS 4
- .nf
- #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");
- .fi
- .P
- .RE
- .SH "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.
- .SH RATIONALE
- None.
- .SH "FUTURE DIRECTIONS"
- None.
- .SH "SEE ALSO"
- .IR "Section 2.4" ", " "Signal Concepts",
- .IR "\fIexec\fR\^",
- .IR "\fIsigaction\fR\^(\|)",
- .IR "\fIsigsetjmp\fR\^(\|)"
- .P
- The Base Definitions volume of POSIX.1\(hy2017,
- .IR "\fB<signal.h>\fP"
- .\"
- .SH COPYRIGHT
- 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 .
- .PP
- 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 .