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1 @c Copyright (C) 1988-2020 Free Software Foundation, Inc.
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2 @c This is part of the GCC manual.
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3 @c For copying conditions, see the file gcc.texi.
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4
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5 @node Bugs
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6 @chapter Reporting Bugs
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7 @cindex bugs
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8 @cindex reporting bugs
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9
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10 Your bug reports play an essential role in making GCC reliable.
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11
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12 When you encounter a problem, the first thing to do is to see if it is
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13 already known. @xref{Trouble}. If it isn't known, then you should
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14 report the problem.
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15
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16 @menu
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17 * Criteria: Bug Criteria. Have you really found a bug?
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18 * Reporting: Bug Reporting. How to report a bug effectively.
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19 @end menu
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20
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21 @node Bug Criteria
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22 @section Have You Found a Bug?
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23 @cindex bug criteria
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24
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25 If you are not sure whether you have found a bug, here are some guidelines:
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26
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27 @itemize @bullet
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28 @cindex fatal signal
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29 @cindex core dump
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30 @item
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31 If the compiler gets a fatal signal, for any input whatever, that is a
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32 compiler bug. Reliable compilers never crash.
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33
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34 @cindex invalid assembly code
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35 @cindex assembly code, invalid
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36 @item
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37 If the compiler produces invalid assembly code, for any input whatever
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38 (except an @code{asm} statement), that is a compiler bug, unless the
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39 compiler reports errors (not just warnings) which would ordinarily
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40 prevent the assembler from being run.
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41
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42 @cindex undefined behavior
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43 @cindex undefined function value
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44 @cindex increment operators
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45 @item
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46 If the compiler produces valid assembly code that does not correctly
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47 execute the input source code, that is a compiler bug.
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48
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49 However, you must double-check to make sure, because you may have a
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50 program whose behavior is undefined, which happened by chance to give
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51 the desired results with another C or C++ compiler.
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52
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53 For example, in many nonoptimizing compilers, you can write @samp{x;}
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54 at the end of a function instead of @samp{return x;}, with the same
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55 results. But the value of the function is undefined if @code{return}
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56 is omitted; it is not a bug when GCC produces different results.
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57
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58 Problems often result from expressions with two increment operators,
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59 as in @code{f (*p++, *p++)}. Your previous compiler might have
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60 interpreted that expression the way you intended; GCC might
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61 interpret it another way. Neither compiler is wrong. The bug is
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62 in your code.
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63
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64 After you have localized the error to a single source line, it should
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65 be easy to check for these things. If your program is correct and
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66 well defined, you have found a compiler bug.
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67
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68 @item
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69 If the compiler produces an error message for valid input, that is a
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70 compiler bug.
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71
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72 @cindex invalid input
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73 @item
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74 If the compiler does not produce an error message for invalid input,
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75 that is a compiler bug. However, you should note that your idea of
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76 ``invalid input'' might be someone else's idea of ``an extension'' or
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77 ``support for traditional practice''.
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78
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79 @item
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80 If you are an experienced user of one of the languages GCC supports, your
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81 suggestions for improvement of GCC are welcome in any case.
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82 @end itemize
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83
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84 @node Bug Reporting
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85 @section How and Where to Report Bugs
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86 @cindex compiler bugs, reporting
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87
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88 Bugs should be reported to the bug database at @value{BUGURL}.
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