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diff --git a/contrib/gcc/doc/bugreport.texi b/contrib/gcc/doc/bugreport.texi new file mode 100644 index 000000000000..1ac26c5fa5df --- /dev/null +++ b/contrib/gcc/doc/bugreport.texi @@ -0,0 +1,394 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +@c 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Bugs +@chapter Reporting Bugs +@cindex bugs +@cindex reporting bugs + +Your bug reports play an essential role in making GCC reliable. + +When you encounter a problem, the first thing to do is to see if it is +already known. @xref{Trouble}. If it isn't known, then you should +report the problem. + +Reporting a bug may help you by bringing a solution to your problem, or +it may not. (If it does not, look in the service directory; see +@ref{Service}.) In any case, the principal function of a bug report is +to help the entire community by making the next version of GCC work +better. Bug reports are your contribution to the maintenance of GCC@. + +Since the maintainers are very overloaded, we cannot respond to every +bug report. However, if the bug has not been fixed, we are likely to +send you a patch and ask you to tell us whether it works. + +In order for a bug report to serve its purpose, you must include the +information that makes for fixing the bug. + +@menu +* Criteria: Bug Criteria. Have you really found a bug? +* Where: Bug Lists. Where to send your bug report. +* Reporting: Bug Reporting. How to report a bug effectively. +* GNATS: gccbug. You can use a bug reporting tool. +* Known: Trouble. Known problems. +* Help: Service. Where to ask for help. +@end menu + +@node Bug Criteria,Bug Lists,,Bugs +@section Have You Found a Bug? +@cindex bug criteria + +If you are not sure whether you have found a bug, here are some guidelines: + +@itemize @bullet +@cindex fatal signal +@cindex core dump +@item +If the compiler gets a fatal signal, for any input whatever, that is a +compiler bug. Reliable compilers never crash. + +@cindex invalid assembly code +@cindex assembly code, invalid +@item +If the compiler produces invalid assembly code, for any input whatever +(except an @code{asm} statement), that is a compiler bug, unless the +compiler reports errors (not just warnings) which would ordinarily +prevent the assembler from being run. + +@cindex undefined behavior +@cindex undefined function value +@cindex increment operators +@item +If the compiler produces valid assembly code that does not correctly +execute the input source code, that is a compiler bug. + +However, you must double-check to make sure, because you may have run +into an incompatibility between GNU C and traditional C +(@pxref{Incompatibilities}). These incompatibilities might be considered +bugs, but they are inescapable consequences of valuable features. + +Or you may have a program whose behavior is undefined, which happened +by chance to give the desired results with another C or C++ compiler. + +For example, in many nonoptimizing compilers, you can write @samp{x;} +at the end of a function instead of @samp{return x;}, with the same +results. But the value of the function is undefined if @code{return} +is omitted; it is not a bug when GCC produces different results. + +Problems often result from expressions with two increment operators, +as in @code{f (*p++, *p++)}. Your previous compiler might have +interpreted that expression the way you intended; GCC might +interpret it another way. Neither compiler is wrong. The bug is +in your code. + +After you have localized the error to a single source line, it should +be easy to check for these things. If your program is correct and +well defined, you have found a compiler bug. + +@item +If the compiler produces an error message for valid input, that is a +compiler bug. + +@cindex invalid input +@item +If the compiler does not produce an error message for invalid input, +that is a compiler bug. However, you should note that your idea of +``invalid input'' might be my idea of ``an extension'' or ``support +for traditional practice''. + +@item +If you are an experienced user of one of the languages GCC supports, your +suggestions for improvement of GCC are welcome in any case. +@end itemize + +@node Bug Lists,Bug Reporting,Bug Criteria,Bugs +@section Where to Report Bugs +@cindex bug report mailing lists +@kindex gcc-bugs@@gcc.gnu.org or bug-gcc@@gnu.org +Send bug reports for the GNU Compiler Collection to +@email{gcc-bugs@@gcc.gnu.org}. In accordance with the GNU-wide +convention, in which bug reports for tool ``foo'' are sent +to @samp{bug-foo@@gnu.org}, the address @email{bug-gcc@@gnu.org} +may also be used; it will forward to the address given above. + +Please read @uref{http://gcc.gnu.org/bugs.html} for additional and/or +more up-to-date bug reporting instructions before you post a bug report. + +@node Bug Reporting,gccbug,Bug Lists,Bugs +@section How to Report Bugs +@cindex compiler bugs, reporting + +The fundamental principle of reporting bugs usefully is this: +@strong{report all the facts}. If you are not sure whether to state a +fact or leave it out, state it! + +Often people omit facts because they think they know what causes the +problem and they conclude that some details don't matter. Thus, you might +assume that the name of the variable you use in an example does not matter. +Well, probably it doesn't, but one cannot be sure. Perhaps the bug is a +stray memory reference which happens to fetch from the location where that +name is stored in memory; perhaps, if the name were different, the contents +of that location would fool the compiler into doing the right thing despite +the bug. Play it safe and give a specific, complete example. That is the +easiest thing for you to do, and the most helpful. + +Keep in mind that the purpose of a bug report is to enable someone to +fix the bug if it is not known. It isn't very important what happens if +the bug is already known. Therefore, always write your bug reports on +the assumption that the bug is not known. + +Sometimes people give a few sketchy facts and ask, ``Does this ring a +bell?'' This cannot help us fix a bug, so it is basically useless. We +respond by asking for enough details to enable us to investigate. +You might as well expedite matters by sending them to begin with. + +Try to make your bug report self-contained. If we have to ask you for +more information, it is best if you include all the previous information +in your response, as well as the information that was missing. + +Please report each bug in a separate message. This makes it easier for +us to track which bugs have been fixed and to forward your bugs reports +to the appropriate maintainer. + +To enable someone to investigate the bug, you should include all these +things: + +@itemize @bullet +@item +The version of GCC@. You can get this by running it with the +@option{-v} option. + +Without this, we won't know whether there is any point in looking for +the bug in the current version of GCC@. + +@item +A complete input file that will reproduce the bug. If the bug is in the +C preprocessor, send a source file and any header files that it +requires. If the bug is in the compiler proper (@file{cc1}), send the +preprocessor output generated by adding @option{-save-temps} to the +compilation command (@pxref{Debugging Options}). When you do this, use +the same @option{-I}, @option{-D} or @option{-U} options that you used in +actual compilation. Then send the @var{input}.i or @var{input}.ii files +generated. + +A single statement is not enough of an example. In order to compile it, +it must be embedded in a complete file of compiler input; and the bug +might depend on the details of how this is done. + +Without a real example one can compile, all anyone can do about your bug +report is wish you luck. It would be futile to try to guess how to +provoke the bug. For example, bugs in register allocation and reloading +frequently depend on every little detail of the function they happen in. + +Even if the input file that fails comes from a GNU program, you should +still send the complete test case. Don't ask the GCC maintainers to +do the extra work of obtaining the program in question---they are all +overworked as it is. Also, the problem may depend on what is in the +header files on your system; it is unreliable for the GCC maintainers +to try the problem with the header files available to them. By sending +CPP output, you can eliminate this source of uncertainty and save us +a certain percentage of wild goose chases. + +@item +The command arguments you gave GCC to compile that example +and observe the bug. For example, did you use @option{-O}? To guarantee +you won't omit something important, list all the options. + +If we were to try to guess the arguments, we would probably guess wrong +and then we would not encounter the bug. + +@item +The type of machine you are using, and the operating system name and +version number. + +@item +The operands you gave to the @code{configure} command when you installed +the compiler. + +@item +A complete list of any modifications you have made to the compiler +source. (We don't promise to investigate the bug unless it happens in +an unmodified compiler. But if you've made modifications and don't tell +us, then you are sending us on a wild goose chase.) + +Be precise about these changes. A description in English is not +enough---send a context diff for them. + +Adding files of your own (such as a machine description for a machine we +don't support) is a modification of the compiler source. + +@item +Details of any other deviations from the standard procedure for installing +GCC@. + +@item +A description of what behavior you observe that you believe is +incorrect. For example, ``The compiler gets a fatal signal,'' or, +``The assembler instruction at line 208 in the output is incorrect.'' + +Of course, if the bug is that the compiler gets a fatal signal, then one +can't miss it. But if the bug is incorrect output, the maintainer might +not notice unless it is glaringly wrong. None of us has time to study +all the assembler code from a 50-line C program just on the chance that +one instruction might be wrong. We need @emph{you} to do this part! + +Even if the problem you experience is a fatal signal, you should still +say so explicitly. Suppose something strange is going on, such as, your +copy of the compiler is out of synch, or you have encountered a bug in +the C library on your system. (This has happened!) Your copy might +crash and the copy here would not. If you @i{said} to expect a crash, +then when the compiler here fails to crash, we would know that the bug +was not happening. If you don't say to expect a crash, then we would +not know whether the bug was happening. We would not be able to draw +any conclusion from our observations. + +If the problem is a diagnostic when compiling GCC with some other +compiler, say whether it is a warning or an error. + +Often the observed symptom is incorrect output when your program is run. +Sad to say, this is not enough information unless the program is short +and simple. None of us has time to study a large program to figure out +how it would work if compiled correctly, much less which line of it was +compiled wrong. So you will have to do that. Tell us which source line +it is, and what incorrect result happens when that line is executed. A +person who understands the program can find this as easily as finding a +bug in the program itself. + +@item +If you send examples of assembler code output from GCC, +please use @option{-g} when you make them. The debugging information +includes source line numbers which are essential for correlating the +output with the input. + +@item +If you wish to mention something in the GCC source, refer to it by +context, not by line number. + +The line numbers in the development sources don't match those in your +sources. Your line numbers would convey no useful information to the +maintainers. + +@item +Additional information from a debugger might enable someone to find a +problem on a machine which he does not have available. However, you +need to think when you collect this information if you want it to have +any chance of being useful. + +@cindex backtrace for bug reports +For example, many people send just a backtrace, but that is never +useful by itself. A simple backtrace with arguments conveys little +about GCC because the compiler is largely data-driven; the same +functions are called over and over for different RTL insns, doing +different things depending on the details of the insn. + +Most of the arguments listed in the backtrace are useless because they +are pointers to RTL list structure. The numeric values of the +pointers, which the debugger prints in the backtrace, have no +significance whatever; all that matters is the contents of the objects +they point to (and most of the contents are other such pointers). + +In addition, most compiler passes consist of one or more loops that +scan the RTL insn sequence. The most vital piece of information about +such a loop---which insn it has reached---is usually in a local variable, +not in an argument. + +@findex debug_rtx +What you need to provide in addition to a backtrace are the values of +the local variables for several stack frames up. When a local +variable or an argument is an RTX, first print its value and then use +the GDB command @code{pr} to print the RTL expression that it points +to. (If GDB doesn't run on your machine, use your debugger to call +the function @code{debug_rtx} with the RTX as an argument.) In +general, whenever a variable is a pointer, its value is no use +without the data it points to. +@end itemize + +Here are some things that are not necessary: + +@itemize @bullet +@item +A description of the envelope of the bug. + +Often people who encounter a bug spend a lot of time investigating +which changes to the input file will make the bug go away and which +changes will not affect it. + +This is often time consuming and not very useful, because the way we +will find the bug is by running a single example under the debugger with +breakpoints, not by pure deduction from a series of examples. You might +as well save your time for something else. + +Of course, if you can find a simpler example to report @emph{instead} of +the original one, that is a convenience. Errors in the output will be +easier to spot, running under the debugger will take less time, etc. +Most GCC bugs involve just one function, so the most straightforward +way to simplify an example is to delete all the function definitions +except the one where the bug occurs. Those earlier in the file may be +replaced by external declarations if the crucial function depends on +them. (Exception: inline functions may affect compilation of functions +defined later in the file.) + +However, simplification is not vital; if you don't want to do this, +report the bug anyway and send the entire test case you used. + +@item +In particular, some people insert conditionals @samp{#ifdef BUG} around +a statement which, if removed, makes the bug not happen. These are just +clutter; we won't pay any attention to them anyway. Besides, you should +send us cpp output, and that can't have conditionals. + +@item +A patch for the bug. + +A patch for the bug is useful if it is a good one. But don't omit the +necessary information, such as the test case, on the assumption that a +patch is all we need. We might see problems with your patch and decide +to fix the problem another way, or we might not understand it at all. + +Sometimes with a program as complicated as GCC it is very hard to +construct an example that will make the program follow a certain path +through the code. If you don't send the example, we won't be able to +construct one, so we won't be able to verify that the bug is fixed. + +And if we can't understand what bug you are trying to fix, or why your +patch should be an improvement, we won't install it. A test case will +help us to understand. + +See @uref{http://gcc.gnu.org/contribute.html} +for guidelines on how to make it easy for us to +understand and install your patches. + +@item +A guess about what the bug is or what it depends on. + +Such guesses are usually wrong. Even I can't guess right about such +things without first using the debugger to find the facts. + +@item +A core dump file. + +We have no way of examining a core dump for your type of machine +unless we have an identical system---and if we do have one, +we should be able to reproduce the crash ourselves. +@end itemize + +@node gccbug,, Bug Reporting, Bugs +@section The gccbug script +@cindex gccbug script + +To simplify creation of bug reports, and to allow better tracking of +reports, we use the GNATS bug tracking system. Part of that system is +the @code{gccbug} script. This is a Unix shell script, so you need a +shell to run it. It is normally installed in the same directory where +@code{gcc} is installed. + +The gccbug script is derived from send-pr, @pxref{using +send-pr,,Creating new Problem Reports,send-pr,Reporting Problems}. When +invoked, it starts a text editor so you can fill out the various fields +of the report. When the you quit the editor, the report is automatically +send to the bug reporting address. + +A number of fields in this bug report form are specific to GCC, and are +explained at @uref{http://gcc.gnu.org/gnats.html}. |