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117 lines
5.8 KiB
HTML
117 lines
5.8 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Free Software" and "Free Software Needs
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Free Documentation", with the Front-Cover Texts being "A GNU Manual,"
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and with the Back-Cover Texts as in (a) below.
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(a) The FSF's Back-Cover Text is: "You are free to copy and modify
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this GNU Manual. Buying copies from GNU Press supports the FSF in
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developing GNU and promoting software freedom." -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Optimized Code (Debugging with GDB)</title>
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<meta name="description" content="Optimized Code (Debugging with GDB)">
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<meta name="keywords" content="Optimized Code (Debugging with GDB)">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="index.html#Top" rel="up" title="Top">
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<link href="Inline-Functions.html#Inline-Functions" rel="next" title="Inline Functions">
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<link href="Value-Sizes.html#Value-Sizes" rel="prev" title="Value Sizes">
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</style>
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</head>
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<body lang="en">
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<a name="Optimized-Code"></a>
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<div class="header">
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<p>
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Next: <a href="Macros.html#Macros" accesskey="n" rel="next">Macros</a>, Previous: <a href="Data.html#Data" accesskey="p" rel="prev">Data</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Debugging-Optimized-Code"></a>
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<h2 class="chapter">11 Debugging Optimized Code</h2>
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<a name="index-optimized-code_002c-debugging"></a>
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<a name="index-debugging-optimized-code"></a>
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<p>Almost all compilers support optimization. With optimization
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disabled, the compiler generates assembly code that corresponds
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directly to your source code, in a simplistic way. As the compiler
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applies more powerful optimizations, the generated assembly code
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diverges from your original source code. With help from debugging
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information generated by the compiler, <small>GDB</small> can map from
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the running program back to constructs from your original source.
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</p>
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<p><small>GDB</small> is more accurate with optimization disabled. If you
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can recompile without optimization, it is easier to follow the
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progress of your program during debugging. But, there are many cases
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where you may need to debug an optimized version.
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</p>
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<p>When you debug a program compiled with ‘<samp>-g -O</samp>’, remember that the
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optimizer has rearranged your code; the debugger shows you what is
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really there. Do not be too surprised when the execution path does not
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exactly match your source file! An extreme example: if you define a
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variable, but never use it, <small>GDB</small> never sees that
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variable—because the compiler optimizes it out of existence.
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</p>
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<p>Some things do not work as well with ‘<samp>-g -O</samp>’ as with just
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‘<samp>-g</samp>’, particularly on machines with instruction scheduling. If in
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doubt, recompile with ‘<samp>-g</samp>’ alone, and if this fixes the problem,
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please report it to us as a bug (including a test case!).
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See <a href="Variables.html#Variables">Variables</a>, for more information about debugging optimized code.
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</p>
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<table class="menu" border="0" cellspacing="0">
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<tr><td align="left" valign="top">• <a href="Inline-Functions.html#Inline-Functions" accesskey="1">Inline Functions</a>:</td><td> </td><td align="left" valign="top">How <small>GDB</small> presents inlining
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Tail-Call-Frames.html#Tail-Call-Frames" accesskey="2">Tail Call Frames</a>:</td><td> </td><td align="left" valign="top"><small>GDB</small> analysis of jumps to functions
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</td></tr>
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</table>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Macros.html#Macros" accesskey="n" rel="next">Macros</a>, Previous: <a href="Data.html#Data" accesskey="p" rel="prev">Data</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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