106 lines
8.5 KiB
HTML
106 lines
8.5 KiB
HTML
<!DOCTYPE html>
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>汇编声明</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_language_asm skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading">汇编声明</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-language.html">language</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<p><i>汇编（asm）声明</i> 给予在 C++ 程序中嵌入汇编语言源代码的能力。此声明受条件性支持且由实现定义，意思是它可以不存在，而且即使实现有所提供，它也并不拥有固定的含义。</p>
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<h3><span class="mw-headline" id=".E8.AF.AD.E6.B3.95">语法</span></h3>
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<tr class="t-sdsc">
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<td class="t-sdsc-nopad"><span class="t-spar">属性</span><span class="t-mark">(可选)</span> <code><b>asm (</b></code> <span class="t-spar">字符串字面量</span> <code><b>)</b></code> <code><b>;</b></code></td>
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<td class="t-sdsc-nopad"></td>
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<td class="t-sdsc-nopad"></td>
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<td colspan="10" class="t-sdsc-sep"></td>
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<table class="t-par-begin">
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<tr class="t-par">
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<td><span class="t-spar">属性</span></td>
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<td>-</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span> 任意数量的<a href="cpp-language-attributes.html">属性</a></td>
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</tr>
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<tr class="t-par">
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<td><span class="t-spar">字符串字面量</span></td>
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<td>-</td>
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<td>一个<a href="cpp-language-string_literal.html">字符串字面量</a></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.A7.A3.E9.87.8A">解释</span></h3>
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<p><span class="t-spar">字符串字面量</span> 通常是以汇编语言编写的短程序，该程序会在执行这条声明时执行。不同的 C++ 编译器的汇编声明规则有巨大差异，和与周围的 C++ 代码之间交互的约定也不同。</p>
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<p>与其他<a href="cpp-language-declarations.html">块声明</a>一样，该声明可出现于块（函数体或其他复合语句）内，并且与所有其他声明一样，此声明也可以在块外出现。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<p>这里演示 GCC 提供的两种内联汇编语法。此程序只在 x86-64 上的 Linux 下正确工作。</p>
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="kw4">extern</span> <span class="st0">"C"</span> <span class="kw4">int</span> func<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// func 的定义以汇编语言书写</span>
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<span class="co1">// 原始字符串字面量可以很有用</span>
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asm<span class="br0">(</span>R<span class="st0">"(
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.globl func
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.type func, @function
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func:
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.cfi_startproc
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movl $7, %eax
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ret
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.cfi_endproc
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)"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">int</span> n <span class="sy1">=</span> func<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 扩展内联汇编</span>
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asm <span class="br0">(</span><span class="st0">"leal (%0,%0,4),%0"</span>
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<span class="sy4">:</span> <span class="st0">"=r"</span> <span class="br0">(</span>n<span class="br0">)</span>
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<span class="sy4">:</span> <span class="st0">"0"</span> <span class="br0">(</span>n<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"7*5 = "</span> <span class="sy1"><<</span> n <span class="sy1"><<</span> <a href="cpp-io-manip-endl.html"><span class="kw1791">std::<span class="me2">endl</span></span></a><span class="sy4">;</span> <span class="co1">// 冲刷缓冲区是有意的</span>
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<span class="co1">// 标准内联汇编</span>
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asm <span class="br0">(</span><span class="st0">"movq $60, %rax<span class="es1">\n</span><span class="es1">\t</span>"</span> <span class="co1">// Linux 上的“退出”的系统调用序号</span>
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<span class="st0">"movq $2, %rdi<span class="es1">\n</span><span class="es1">\t</span>"</span> <span class="co1">// 此程序返回 2</span>
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<span class="st0">"syscall"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">7*5 = 35</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.A4.96.E9.83.A8.E9.93.BE.E6.8E.A5">外部链接</span></h3>
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<ul>
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<li><a rel="nofollow" class="external text" href="http://www.ibiblio.org/gferg/ldp/GCC-Inline-Assembly-HOWTO.html">GCC 内联汇编 HOWTO</a></li>
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<li><a rel="nofollow" class="external text" href="http://pic.dhe.ibm.com/infocenter/comphelp/v121v141/topic/com.ibm.xlcpp121.aix.doc/language_ref/asm.html">IBM XL C/C++ 内联汇编</a></li>
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<li><a rel="nofollow" class="external text" href="https://software.intel.com/en-us/cpp-compiler-developer-guide-and-reference-inline-assembly">Intel C++ 内联汇编</a></li>
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<li><a rel="nofollow" class="external text" href="http://msdn.microsoft.com/en-us/library/4ks26t93(v=vs.120).aspx">Visual Studio 2013 内联汇编器</a></li>
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<li><a rel="nofollow" class="external text" href="https://blogs.oracle.com/x86be/entry/gcc_style_asm_inlining_support">Sun Studio 12 Asm 语句</a></li>
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<li><a rel="nofollow" class="external text" href="http://h21007.www2.hp.com/portal/site/dspp/menuitem.863c3e4cbcdc3f3515b49c108973a801?ciid=4308e2f5bde02110e2f5bde02110275d6e10RCRD">基于 Itanium 的 HP-UX 的内联汇编</a></li>
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</ul>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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