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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>sigaltstack</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_008_597"> </a>NAME</h4><blockquote>sigaltstack - set and/or get signal alternate stack context.</blockquote><h4><a name = "tag_000_008_598"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="signal.h.html">signal.h</a>>int sigaltstack(const stack_t *<i>ss</i>, stack_t *<i>oss</i>);</code></pre></blockquote><h4><a name = "tag_000_008_599"> </a>DESCRIPTION</h4><blockquote>The<i>sigaltstack()</i>function allows a process to defineand examine the state of an alternate stack for signal handlers.Signals that have been explicitly declared to execute on the alternatestack will be delivered on the alternate stack.<p>If <i>ss</i> is not a null pointer, it points to a <b>stack_t</b> structurethat specifies the alternate signal stack that will take effect upon returnfrom<i>sigaltstack()</i>.The <b>ss_flags</b> member specifies the new stack state. If it is set toSS_DISABLE, the stack is disabled and <b>ss_sp</b> and <b>ss_size</b> areignored. Otherwise the stack will be enabled, and the <b>ss_sp</b> and<b>ss_size</b> members specify the new address and size of the stack.<p>The range of addresses starting at <b>ss_sp</b>, up to but not including<b>ss_sp</b>+<b>ss_size</b>, is available to the implementation for use asthe stack. This interface makes no assumptions regarding which end is thestack base and in which direction the stack grows as items are pushed.<p>If <i>oss</i> is not a null pointer, on successful completion itwill point to a <b>stack_t</b> structure that specifies the alternate signalstack that was in effect prior to the call to<i>sigaltstack()</i>.The <b>ss_sp</b> and <b>ss_size</b> members specify the address and size ofthat stack. The <b>ss_flags</b> member specifies the stack's state, and maycontain one of the following values:<dl compact><dt>SS_ONSTACK<dd>The process is currently executing on the alternate signal stack. Attempts tomodify the alternate signal stack while the process is executing on it fails.This flag must not be modified by processes.<dt>SS_DISABLE<dd>The alternate signal stack is currently disabled.</dl><p>The value SIGSTKSZ is a system default specifying the number of bytes thatwould be used to cover the usual case when manually allocating an alternatestack area. The value MINSIGSTKSZ is defined to be the minimum stack size fora signal handler. In computing an alternate stack size, a program should addthat amount to its stack requirements to allow for the system implementationoverhead. The constants SS_ONSTACK, SS_DISABLE, SIGSTKSZ, and MINSIGSTKSZ aredefined in<i><a href="signal.h.html"><signal.h></a></i>.<p>After a successful call to one of the<i>exec</i>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 thealternate stack) will always execute on the alternate stack if it is deliveredwhile another signal is being caught using the alternate stack.<p>Use of this function by library threads that are not bound tokernel-scheduled entities results in undefined behaviour.</blockquote><h4><a name = "tag_000_008_600"> </a>RETURN VALUE</h4><blockquote>Upon successful completion,<i>sigaltstack()</i>returns 0. Otherwise, it returns -1 and sets <i>errno</i> to indicate theerror.<br></blockquote><h4><a name = "tag_000_008_601"> </a>ERRORS</h4><blockquote>The<i>sigaltstack()</i>function will fail if:<dl compact><dt>[EINVAL]<dd>The <i>ss</i> argument is not a null pointer, and the <b>ss_flags</b> memberpointed to by <i>ss</i> contains flags other than SS_DISABLE.<dt>[ENOMEM]<dd>The size of the alternate stack area is less than MINSIGSTKSZ.<dt>[EPERM]<dd>An attempt was made to modify an active stack.</dl></blockquote><h4><a name = "tag_000_008_602"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_008_603"> </a>APPLICATION USAGE</h4><blockquote>The following code fragment illustrates a method for allocatingmemory for an alternate stack:<pre><code>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");</code></pre>On some implementations, stack space is automatically extended as needed. Onthose implementations, automatic extension is typically not available for analternate stack. If the stack overflows, the behaviour is undefined.</blockquote><h4><a name = "tag_000_008_604"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_008_605"> </a>SEE ALSO</h4><blockquote><i><a href="sigaction.html">sigaction()</a></i>,<i><a href="sigsetjmp.html">sigsetjmp()</a></i>,<i><a href="signal.h.html"><signal.h></a></i>.</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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