1@c Copyright (C) 1988-2015 Free Software Foundation, Inc.
2@c This is part of the GCC manual.
3@c For copying conditions, see the file gcc.texi.
4
5@node Bugs
6@chapter Reporting Bugs
7@cindex bugs
8@cindex reporting bugs
9
10Your bug reports play an essential role in making GCC reliable.
11
12When you encounter a problem, the first thing to do is to see if it is
13already known.  @xref{Trouble}.  If it isn't known, then you should
14report the problem.
15
16@menu
17* Criteria:  Bug Criteria.   Have you really found a bug?
18* Reporting: Bug Reporting.  How to report a bug effectively.
19@end menu
20
21@node Bug Criteria
22@section Have You Found a Bug?
23@cindex bug criteria
24
25If you are not sure whether you have found a bug, here are some guidelines:
26
27@itemize @bullet
28@cindex fatal signal
29@cindex core dump
30@item
31If the compiler gets a fatal signal, for any input whatever, that is a
32compiler bug.  Reliable compilers never crash.
33
34@cindex invalid assembly code
35@cindex assembly code, invalid
36@item
37If the compiler produces invalid assembly code, for any input whatever
38(except an @code{asm} statement), that is a compiler bug, unless the
39compiler reports errors (not just warnings) which would ordinarily
40prevent the assembler from being run.
41
42@cindex undefined behavior
43@cindex undefined function value
44@cindex increment operators
45@item
46If the compiler produces valid assembly code that does not correctly
47execute the input source code, that is a compiler bug.
48
49However, you must double-check to make sure, because you may have a
50program whose behavior is undefined, which happened by chance to give
51the desired results with another C or C++ compiler.
52
53For example, in many nonoptimizing compilers, you can write @samp{x;}
54at the end of a function instead of @samp{return x;}, with the same
55results.  But the value of the function is undefined if @code{return}
56is omitted; it is not a bug when GCC produces different results.
57
58Problems often result from expressions with two increment operators,
59as in @code{f (*p++, *p++)}.  Your previous compiler might have
60interpreted that expression the way you intended; GCC might
61interpret it another way.  Neither compiler is wrong.  The bug is
62in your code.
63
64After you have localized the error to a single source line, it should
65be easy to check for these things.  If your program is correct and
66well defined, you have found a compiler bug.
67
68@item
69If the compiler produces an error message for valid input, that is a
70compiler bug.
71
72@cindex invalid input
73@item
74If the compiler does not produce an error message for invalid input,
75that is a compiler bug.  However, you should note that your idea of
76``invalid input'' might be someone else's idea of ``an extension'' or
77``support for traditional practice''.
78
79@item
80If you are an experienced user of one of the languages GCC supports, your
81suggestions for improvement of GCC are welcome in any case.
82@end itemize
83
84@node Bug Reporting
85@section How and Where to Report Bugs
86@cindex compiler bugs, reporting
87
88Bugs should be reported to the bug database at @value{BUGURL}.
89