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143 lines
6.1 KiB
HTML
143 lines
6.1 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) 1988-2018 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 "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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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>Bug Criteria (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="Bug Criteria (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="Bug Criteria (Using the GNU Compiler Collection (GCC))">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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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="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Bugs.html#Bugs" rel="up" title="Bugs">
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<link href="Bug-Reporting.html#Bug-Reporting" rel="next" title="Bug Reporting">
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<link href="Bugs.html#Bugs" rel="prev" title="Bugs">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Bug-Criteria"></a>
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<div class="header">
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<p>
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Next: <a href="Bug-Reporting.html#Bug-Reporting" accesskey="n" rel="next">Bug Reporting</a>, Up: <a href="Bugs.html#Bugs" accesskey="u" rel="up">Bugs</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Have-You-Found-a-Bug_003f"></a>
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<h3 class="section">14.1 Have You Found a Bug?</h3>
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<a name="index-bug-criteria"></a>
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<p>If you are not sure whether you have found a bug, here are some guidelines:
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</p>
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<ul>
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<li> <a name="index-fatal-signal"></a>
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<a name="index-core-dump"></a>
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If the compiler gets a fatal signal, for any input whatever, that is a
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compiler bug. Reliable compilers never crash.
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</li><li> <a name="index-invalid-assembly-code"></a>
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<a name="index-assembly-code_002c-invalid"></a>
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If the compiler produces invalid assembly code, for any input whatever
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(except an <code>asm</code> statement), that is a compiler bug, unless the
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compiler reports errors (not just warnings) which would ordinarily
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prevent the assembler from being run.
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</li><li> <a name="index-undefined-behavior"></a>
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<a name="index-undefined-function-value"></a>
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<a name="index-increment-operators"></a>
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If the compiler produces valid assembly code that does not correctly
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execute the input source code, that is a compiler bug.
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<p>However, you must double-check to make sure, because you may have a
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program whose behavior is undefined, which happened by chance to give
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the desired results with another C or C++ compiler.
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</p>
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<p>For example, in many nonoptimizing compilers, you can write ‘<samp>x;</samp>’
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at the end of a function instead of ‘<samp>return x;</samp>’, with the same
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results. But the value of the function is undefined if <code>return</code>
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is omitted; it is not a bug when GCC produces different results.
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</p>
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<p>Problems often result from expressions with two increment operators,
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as in <code>f (*p++, *p++)</code>. Your previous compiler might have
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interpreted that expression the way you intended; GCC might
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interpret it another way. Neither compiler is wrong. The bug is
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in your code.
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</p>
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<p>After you have localized the error to a single source line, it should
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be easy to check for these things. If your program is correct and
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well defined, you have found a compiler bug.
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</p>
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</li><li> If the compiler produces an error message for valid input, that is a
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compiler bug.
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</li><li> <a name="index-invalid-input"></a>
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If the compiler does not produce an error message for invalid input,
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that is a compiler bug. However, you should note that your idea of
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“invalid input” might be someone else’s idea of “an extension” or
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“support for traditional practice”.
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</li><li> If you are an experienced user of one of the languages GCC supports, your
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suggestions for improvement of GCC are welcome in any case.
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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="Bug-Reporting.html#Bug-Reporting" accesskey="n" rel="next">Bug Reporting</a>, Up: <a href="Bugs.html#Bugs" accesskey="u" rel="up">Bugs</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-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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