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Ref-docs/POSIX/susv3/functions/sigaltstack.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta name="generator" content="HTML Tidy, see www.w3.org">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>sigaltstack</title>
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</head>
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<body bgcolor="white">
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<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
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</script>
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<basefont size="3"> <a name="sigaltstack"></a> <a name="tag_03_682"></a><!-- sigaltstack -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_682_01"></a>NAME</h4>
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<blockquote>sigaltstack - set and get signal alternate stack context</blockquote>
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<h4><a name="tag_03_682_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/signal.h.html">signal.h</a>><br>
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<br>
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int sigaltstack(const stack_t *restrict</tt> <i>ss</i><tt>, stack_t *restrict</tt> <i>oss</i><tt>); <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_682_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>sigaltstack</i>() function allows a process to define and examine the state of an alternate stack for signal handlers.
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Signals that have been explicitly declared to execute on the alternate stack shall be delivered on the alternate stack.</p>
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<p>If <i>ss</i> is not a null pointer, it points to a <b>stack_t</b> structure that specifies the alternate signal stack that shall
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take effect upon return from <i>sigaltstack</i>(). The <i>ss_flags</i> member specifies the new stack state. If it is set to
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SS_DISABLE, the stack is disabled and <i>ss_sp</i> and <i>ss_size</i> are ignored. Otherwise, the stack shall be enabled, and the
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<i>ss_sp</i> and <i>ss_size</i> members specify the new address and size of the stack.</p>
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<p>The range of addresses starting at <i>ss_sp</i> up to but not including <i>ss_sp</i>+ <i>ss_size</i> is available to the
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implementation for use as the stack. This function makes no assumptions regarding which end is the stack base and in which
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direction the stack grows as items are pushed.</p>
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<p>If <i>oss</i> is not a null pointer, on successful completion it shall point to a <b>stack_t</b> structure that specifies the
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alternate signal stack that was in effect prior to the call to <i>sigaltstack</i>(). The <i>ss_sp</i> and <i>ss_size</i> members
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specify the address and size of that stack. The <i>ss_flags</i> member specifies the stack's state, and may contain one of the
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following values:</p>
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<dl compact>
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<dt>SS_ONSTACK</dt>
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<dd>The process is currently executing on the alternate signal stack. 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 processes.</dd>
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<dt>SS_DISABLE</dt>
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<dd>The alternate signal stack is currently disabled.</dd>
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</dl>
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<p>The value SIGSTKSZ is a system default specifying the number of bytes 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 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 to its stack requirements to allow for the system
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implementation overhead. The constants SS_ONSTACK, SS_DISABLE, SIGSTKSZ, and MINSIGSTKSZ are defined in <a href=
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"../basedefs/signal.h.html"><i><signal.h></i></a>.</p>
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<p>After a successful call to one of the <i><a href="../functions/exec.html">exec</a></i> functions, there are no alternate signal
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stacks in the new process image.</p>
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<p>In some implementations, a signal (whether or not indicated to execute 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 using the alternate stack.</p>
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<p>Use of this function by library threads that are not bound to kernel-scheduled entities results in undefined behavior.</p>
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</blockquote>
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<h4><a name="tag_03_682_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>sigaltstack</i>() shall return 0; otherwise, it shall return -1 and set <i>errno</i> to indicate
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the error.</p>
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</blockquote>
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<h4><a name="tag_03_682_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>sigaltstack</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd>The <i>ss</i> argument is not a null pointer, and the <i>ss_flags</i> member pointed to by <i>ss</i> contains flags other than
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SS_DISABLE.</dd>
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<dt>[ENOMEM]</dt>
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<dd>The size of the alternate stack area is less than MINSIGSTKSZ.</dd>
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<dt>[EPERM]</dt>
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<dd>An attempt was made to modify an active stack.</dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_682_06"></a>EXAMPLES</h4>
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<blockquote>
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<h5><a name="tag_03_682_06_01"></a>Allocating Memory for an Alternate Stack</h5>
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<p>The following example illustrates a method for allocating memory for an alternate stack.</p>
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<pre>
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<tt>#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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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_682_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>On some implementations, stack space is automatically extended as needed. On those implementations, automatic extension is
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typically not available for an alternate stack. If the stack overflows, the behavior is undefined.</p>
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</blockquote>
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<h4><a name="tag_03_682_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_682_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_682_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="xsh_chap02_04.html#tag_02_04"><i>Signal Concepts</i></a> , <a href="sigaction.html"><i>sigaction</i>()</a> , <a href=
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"sigsetjmp.html"><i>sigsetjmp</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/signal.h.html"><i><signal.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_682_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 4, Version 2.</p>
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</blockquote>
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<h4><a name="tag_03_682_12"></a>Issue 5</h4>
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<blockquote>
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<p>Moved from X/OPEN UNIX extension to BASE.</p>
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<p>The last sentence of the DESCRIPTION was included as an APPLICATION USAGE note in previous issues.</p>
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</blockquote>
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<h4><a name="tag_03_682_13"></a>Issue 6</h4>
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<blockquote>
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<p>The DESCRIPTION is updated to avoid use of the term "must" for application requirements.</p>
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<p>The <b>restrict</b> keyword is added to the <i>sigaltstack</i>() prototype for alignment with the ISO/IEC 9899:1999
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standard.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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<hr size="2" noshade>
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<center><font size="2"><!--footer start-->
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
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"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
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