mirror of https://github.com/mkerrisk/man-pages
145 lines
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Plaintext
145 lines
5.0 KiB
Plaintext
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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "SIGALTSTACK" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" sigaltstack
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.SH NAME
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sigaltstack \- set and get signal alternate stack context
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.SH SYNOPSIS
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.LP
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\fB#include <signal.h>
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.br
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.sp
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int sigaltstack(const stack_t *restrict\fP \fIss\fP\fB, stack_t *restrict\fP
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\fIoss\fP\fB); \fP
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\fB
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.br
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\fP
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.SH DESCRIPTION
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.LP
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The \fIsigaltstack\fP() function allows a process to define and examine
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the state of an alternate stack for signal handlers for
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the current thread. Signals that have been explicitly declared to
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execute on the alternate stack shall be delivered on the
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alternate stack.
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.LP
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If \fIss\fP is not a null pointer, it points to a \fBstack_t\fP structure
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that specifies the alternate signal stack that shall
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take effect upon return from \fIsigaltstack\fP(). The \fIss_flags\fP
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member specifies the new stack state. If it is set to
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SS_DISABLE, the stack is disabled and \fIss_sp\fP and \fIss_size\fP
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are ignored. Otherwise, the stack shall be enabled, and the
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\fIss_sp\fP and \fIss_size\fP members specify the new address and
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size of the stack.
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.LP
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The range of addresses starting at \fIss_sp\fP up to but not including
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\fIss_sp\fP+ \fIss_size\fP is available to the
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implementation for use as the stack. This function makes no assumptions
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regarding which end is the stack base and in which
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direction the stack grows as items are pushed.
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.LP
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If \fIoss\fP is not a null pointer, on successful completion it shall
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point to a \fBstack_t\fP structure that specifies the
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alternate signal stack that was in effect prior to the call to \fIsigaltstack\fP().
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The \fIss_sp\fP and \fIss_size\fP members
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specify the address and size of that stack. The \fIss_flags\fP member
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specifies the stack's state, and may contain one of the
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following values:
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.TP 7
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SS_ONSTACK
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The process is currently executing on the alternate signal stack.
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Attempts to modify the alternate signal stack while the
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process is executing on it fail. This flag shall not be modified by
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processes.
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.TP 7
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SS_DISABLE
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The alternate signal stack is currently disabled.
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.sp
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.LP
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The value SIGSTKSZ is a system default specifying the number of bytes
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that would be used to cover the usual case when manually
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allocating an alternate stack area. The value MINSIGSTKSZ is defined
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to be the minimum stack size for a signal handler. In
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computing an alternate stack size, a program should add that amount
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to its stack requirements to allow for the system
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implementation overhead. The constants SS_ONSTACK, SS_DISABLE, SIGSTKSZ,
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and MINSIGSTKSZ are defined in \fI<signal.h>\fP.
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.LP
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After a successful call to one of the \fIexec\fP functions, there
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are no alternate signal
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stacks in the new process image.
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.LP
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In some implementations, a signal (whether or not indicated to execute
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on the alternate stack) shall always execute on the
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alternate stack if it is delivered while another signal is being caught
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using the alternate stack.
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.LP
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Use of this function by library threads that are not bound to kernel-scheduled
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entities results in undefined behavior.
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.SH RETURN VALUE
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.LP
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Upon successful completion, \fIsigaltstack\fP() shall return 0; otherwise,
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it shall return -1 and set \fIerrno\fP to indicate
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the error.
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.SH ERRORS
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.LP
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The \fIsigaltstack\fP() function shall fail if:
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.TP 7
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.B EINVAL
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The \fIss\fP argument is not a null pointer, and the \fIss_flags\fP
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member pointed to by \fIss\fP contains flags other than
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SS_DISABLE.
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.TP 7
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.B ENOMEM
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The size of the alternate stack area is less than MINSIGSTKSZ.
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.TP 7
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.B EPERM
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An attempt was made to modify an active stack.
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.sp
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.SS Allocating Memory for an Alternate Stack
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.LP
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The following example illustrates a method for allocating memory for
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an alternate stack.
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.sp
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.RS
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.nf
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\fB#include <signal.h>
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\&...
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if ((sigstk.ss_sp = malloc(SIGSTKSZ)) == NULL)
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/* Error return. */
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sigstk.ss_size = SIGSTKSZ;
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sigstk.ss_flags = 0;
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if (sigaltstack(&sigstk,(stack_t *)0) < 0)
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perror("sigaltstack");
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\fP
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.fi
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.RE
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.SH APPLICATION USAGE
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.LP
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On some implementations, stack space is automatically extended as
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needed. On those implementations, automatic extension is
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typically not available for an alternate stack. If the stack overflows,
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the behavior is undefined.
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.SH RATIONALE
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.LP
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None.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fISignal Concepts\fP , \fIsigaction\fP() , \fIsigsetjmp\fP() , the
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Base Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<signal.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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