1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<!-- Copyright (C) 1988-2021 Free Software Foundation, Inc. 4 5Permission is granted to copy, distribute and/or modify this document 6under the terms of the GNU Free Documentation License, Version 1.3 or 7any later version published by the Free Software Foundation; with the 8Invariant Sections being "Free Software" and "Free Software Needs 9Free Documentation", with the Front-Cover Texts being "A GNU Manual," 10and with the Back-Cover Texts as in (a) below. 11 12(a) The FSF's Back-Cover Text is: "You are free to copy and modify 13this GNU Manual. 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With optimization 76disabled, the compiler generates assembly code that corresponds 77directly to your source code, in a simplistic way. As the compiler 78applies more powerful optimizations, the generated assembly code 79diverges from your original source code. With help from debugging 80information generated by the compiler, <small>GDB</small> can map from 81the running program back to constructs from your original source. 82</p> 83<p><small>GDB</small> is more accurate with optimization disabled. If you 84can recompile without optimization, it is easier to follow the 85progress of your program during debugging. But, there are many cases 86where you may need to debug an optimized version. 87</p> 88<p>When you debug a program compiled with ‘<samp>-g -O</samp>’, remember that the 89optimizer has rearranged your code; the debugger shows you what is 90really there. Do not be too surprised when the execution path does not 91exactly match your source file! An extreme example: if you define a 92variable, but never use it, <small>GDB</small> never sees that 93variable—because the compiler optimizes it out of existence. 94</p> 95<p>Some things do not work as well with ‘<samp>-g -O</samp>’ as with just 96‘<samp>-g</samp>’, particularly on machines with instruction scheduling. If in 97doubt, recompile with ‘<samp>-g</samp>’ alone, and if this fixes the problem, 98please report it to us as a bug (including a test case!). 99See <a href="Variables.html#Variables">Variables</a>, for more information about debugging optimized code. 100</p> 101<table class="menu" border="0" cellspacing="0"> 102<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 103</td></tr> 104<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 105</td></tr> 106</table> 107 108<hr> 109<div class="header"> 110<p> 111Next: <a href="Macros.html#Macros" accesskey="n" rel="next">Macros</a>, Previous: <a href="Data.html#Data" accesskey="p" rel="previous">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> 112</div> 113 114 115 116</body> 117</html> 118