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134 lines
6.4 KiB
HTML
134 lines
6.4 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>Inline Functions (Debugging with GDB)</title>
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<meta name="description" content="Inline Functions (Debugging with GDB)">
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<meta name="keywords" content="Inline Functions (Debugging with GDB)">
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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="Optimized-Code.html#Optimized-Code" rel="up" title="Optimized Code">
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<link href="Tail-Call-Frames.html#Tail-Call-Frames" rel="next" title="Tail Call Frames">
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<link href="Optimized-Code.html#Optimized-Code" rel="prev" title="Optimized Code">
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</style>
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</head>
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<body lang="en">
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<a name="Inline-Functions"></a>
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<div class="header">
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<p>
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Next: <a href="Tail-Call-Frames.html#Tail-Call-Frames" accesskey="n" rel="next">Tail Call Frames</a>, Up: <a href="Optimized-Code.html#Optimized-Code" accesskey="u" rel="up">Optimized Code</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="Inline-Functions-1"></a>
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<h3 class="section">11.1 Inline Functions</h3>
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<a name="index-inline-functions_002c-debugging"></a>
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<p><em>Inlining</em> is an optimization that inserts a copy of the function
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body directly at each call site, instead of jumping to a shared
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routine. <small>GDB</small> displays inlined functions just like
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non-inlined functions. They appear in backtraces. You can view their
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arguments and local variables, step into them with <code>step</code>, skip
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them with <code>next</code>, and escape from them with <code>finish</code>.
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You can check whether a function was inlined by using the
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<code>info frame</code> command.
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</p>
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<p>For <small>GDB</small> to support inlined functions, the compiler must
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record information about inlining in the debug information —
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<small>GCC</small> using the <small>DWARF 2</small> format does this, and several
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other compilers do also. <small>GDB</small> only supports inlined functions
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when using <small>DWARF 2</small>. Versions of <small>GCC</small> before 4.1
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do not emit two required attributes (‘<samp>DW_AT_call_file</samp>’ and
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‘<samp>DW_AT_call_line</samp>’); <small>GDB</small> does not display inlined
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function calls with earlier versions of <small>GCC</small>. It instead
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displays the arguments and local variables of inlined functions as
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local variables in the caller.
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</p>
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<p>The body of an inlined function is directly included at its call site;
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unlike a non-inlined function, there are no instructions devoted to
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the call. <small>GDB</small> still pretends that the call site and the
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start of the inlined function are different instructions. Stepping to
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the call site shows the call site, and then stepping again shows
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the first line of the inlined function, even though no additional
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instructions are executed.
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</p>
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<p>This makes source-level debugging much clearer; you can see both the
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context of the call and then the effect of the call. Only stepping by
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a single instruction using <code>stepi</code> or <code>nexti</code> does not do
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this; single instruction steps always show the inlined body.
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</p>
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<p>There are some ways that <small>GDB</small> does not pretend that inlined
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function calls are the same as normal calls:
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</p>
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<ul>
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<li> Setting breakpoints at the call site of an inlined function may not
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work, because the call site does not contain any code. <small>GDB</small>
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may incorrectly move the breakpoint to the next line of the enclosing
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function, after the call. This limitation will be removed in a future
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version of <small>GDB</small>; until then, set a breakpoint on an earlier line
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or inside the inlined function instead.
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</li><li> <small>GDB</small> cannot locate the return value of inlined calls after
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using the <code>finish</code> command. This is a limitation of compiler-generated
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debugging information; after <code>finish</code>, you can step to the next line
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and print a variable where your program stored the return value.
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</li></ul>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Tail-Call-Frames.html#Tail-Call-Frames" accesskey="n" rel="next">Tail Call Frames</a>, Up: <a href="Optimized-Code.html#Optimized-Code" accesskey="u" rel="up">Optimized Code</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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