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<title>Using the GNU Compiler Collection (GCC): Bug Criteria</title>
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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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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<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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