1 | This is Info file gcc.info, produced by Makeinfo-1.55 from the input |
---|
2 | file gcc.texi. |
---|
3 | |
---|
4 | This file documents the use and the internals of the GNU compiler. |
---|
5 | |
---|
6 | Published by the Free Software Foundation 59 Temple Place - Suite 330 |
---|
7 | Boston, MA 02111-1307 USA |
---|
8 | |
---|
9 | Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995 Free Software |
---|
10 | Foundation, Inc. |
---|
11 | |
---|
12 | Permission is granted to make and distribute verbatim copies of this |
---|
13 | manual provided the copyright notice and this permission notice are |
---|
14 | preserved on all copies. |
---|
15 | |
---|
16 | Permission is granted to copy and distribute modified versions of |
---|
17 | this manual under the conditions for verbatim copying, provided also |
---|
18 | that the sections entitled "GNU General Public License," "Funding for |
---|
19 | Free Software," and "Protect Your Freedom--Fight `Look And Feel'" are |
---|
20 | included exactly as in the original, and provided that the entire |
---|
21 | resulting derived work is distributed under the terms of a permission |
---|
22 | notice identical to this one. |
---|
23 | |
---|
24 | Permission is granted to copy and distribute translations of this |
---|
25 | manual into another language, under the above conditions for modified |
---|
26 | versions, except that the sections entitled "GNU General Public |
---|
27 | License," "Funding for Free Software," and "Protect Your Freedom--Fight |
---|
28 | `Look And Feel'", and this permission notice, may be included in |
---|
29 | translations approved by the Free Software Foundation instead of in the |
---|
30 | original English. |
---|
31 | |
---|
32 | |
---|
33 | File: gcc.info, Node: Temporaries, Prev: Static Definitions, Up: C++ Misunderstandings |
---|
34 | |
---|
35 | Temporaries May Vanish Before You Expect |
---|
36 | ---------------------------------------- |
---|
37 | |
---|
38 | It is dangerous to use pointers or references to *portions* of a |
---|
39 | temporary object. The compiler may very well delete the object before |
---|
40 | you expect it to, leaving a pointer to garbage. The most common place |
---|
41 | where this problem crops up is in classes like the libg++ `String' |
---|
42 | class, that define a conversion function to type `char *' or `const |
---|
43 | char *'. However, any class that returns a pointer to some internal |
---|
44 | structure is potentially subject to this problem. |
---|
45 | |
---|
46 | For example, a program may use a function `strfunc' that returns |
---|
47 | `String' objects, and another function `charfunc' that operates on |
---|
48 | pointers to `char': |
---|
49 | |
---|
50 | String strfunc (); |
---|
51 | void charfunc (const char *); |
---|
52 | |
---|
53 | In this situation, it may seem natural to write |
---|
54 | `charfunc (strfunc ());' based on the knowledge that class `String' has |
---|
55 | an explicit conversion to `char' pointers. However, what really |
---|
56 | happens is akin to `charfunc (strfunc ().convert ());', where the |
---|
57 | `convert' method is a function to do the same data conversion normally |
---|
58 | performed by a cast. Since the last use of the temporary `String' |
---|
59 | object is the call to the conversion function, the compiler may delete |
---|
60 | that object before actually calling `charfunc'. The compiler has no |
---|
61 | way of knowing that deleting the `String' object will invalidate the |
---|
62 | pointer. The pointer then points to garbage, so that by the time |
---|
63 | `charfunc' is called, it gets an invalid argument. |
---|
64 | |
---|
65 | Code like this may run successfully under some other compilers, |
---|
66 | especially those that delete temporaries relatively late. However, the |
---|
67 | GNU C++ behavior is also standard-conforming, so if your program depends |
---|
68 | on late destruction of temporaries it is not portable. |
---|
69 | |
---|
70 | If you think this is surprising, you should be aware that the ANSI |
---|
71 | C++ committee continues to debate the lifetime-of-temporaries problem. |
---|
72 | |
---|
73 | For now, at least, the safe way to write such code is to give the |
---|
74 | temporary a name, which forces it to remain until the end of the scope |
---|
75 | of the name. For example: |
---|
76 | |
---|
77 | String& tmp = strfunc (); |
---|
78 | charfunc (tmp); |
---|
79 | |
---|
80 | |
---|
81 | File: gcc.info, Node: Protoize Caveats, Next: Non-bugs, Prev: C++ Misunderstandings, Up: Trouble |
---|
82 | |
---|
83 | Caveats of using `protoize' |
---|
84 | =========================== |
---|
85 | |
---|
86 | The conversion programs `protoize' and `unprotoize' can sometimes |
---|
87 | change a source file in a way that won't work unless you rearrange it. |
---|
88 | |
---|
89 | * `protoize' can insert references to a type name or type tag before |
---|
90 | the definition, or in a file where they are not defined. |
---|
91 | |
---|
92 | If this happens, compiler error messages should show you where the |
---|
93 | new references are, so fixing the file by hand is straightforward. |
---|
94 | |
---|
95 | * There are some C constructs which `protoize' cannot figure out. |
---|
96 | For example, it can't determine argument types for declaring a |
---|
97 | pointer-to-function variable; this you must do by hand. `protoize' |
---|
98 | inserts a comment containing `???' each time it finds such a |
---|
99 | variable; so you can find all such variables by searching for this |
---|
100 | string. ANSI C does not require declaring the argument types of |
---|
101 | pointer-to-function types. |
---|
102 | |
---|
103 | * Using `unprotoize' can easily introduce bugs. If the program |
---|
104 | relied on prototypes to bring about conversion of arguments, these |
---|
105 | conversions will not take place in the program without prototypes. |
---|
106 | One case in which you can be sure `unprotoize' is safe is when you |
---|
107 | are removing prototypes that were made with `protoize'; if the |
---|
108 | program worked before without any prototypes, it will work again |
---|
109 | without them. |
---|
110 | |
---|
111 | You can find all the places where this problem might occur by |
---|
112 | compiling the program with the `-Wconversion' option. It prints a |
---|
113 | warning whenever an argument is converted. |
---|
114 | |
---|
115 | * Both conversion programs can be confused if there are macro calls |
---|
116 | in and around the text to be converted. In other words, the |
---|
117 | standard syntax for a declaration or definition must not result |
---|
118 | from expanding a macro. This problem is inherent in the design of |
---|
119 | C and cannot be fixed. If only a few functions have confusing |
---|
120 | macro calls, you can easily convert them manually. |
---|
121 | |
---|
122 | * `protoize' cannot get the argument types for a function whose |
---|
123 | definition was not actually compiled due to preprocessing |
---|
124 | conditionals. When this happens, `protoize' changes nothing in |
---|
125 | regard to such a function. `protoize' tries to detect such |
---|
126 | instances and warn about them. |
---|
127 | |
---|
128 | You can generally work around this problem by using `protoize' step |
---|
129 | by step, each time specifying a different set of `-D' options for |
---|
130 | compilation, until all of the functions have been converted. |
---|
131 | There is no automatic way to verify that you have got them all, |
---|
132 | however. |
---|
133 | |
---|
134 | * Confusion may result if there is an occasion to convert a function |
---|
135 | declaration or definition in a region of source code where there |
---|
136 | is more than one formal parameter list present. Thus, attempts to |
---|
137 | convert code containing multiple (conditionally compiled) versions |
---|
138 | of a single function header (in the same vicinity) may not produce |
---|
139 | the desired (or expected) results. |
---|
140 | |
---|
141 | If you plan on converting source files which contain such code, it |
---|
142 | is recommended that you first make sure that each conditionally |
---|
143 | compiled region of source code which contains an alternative |
---|
144 | function header also contains at least one additional follower |
---|
145 | token (past the final right parenthesis of the function header). |
---|
146 | This should circumvent the problem. |
---|
147 | |
---|
148 | * `unprotoize' can become confused when trying to convert a function |
---|
149 | definition or declaration which contains a declaration for a |
---|
150 | pointer-to-function formal argument which has the same name as the |
---|
151 | function being defined or declared. We recommand you avoid such |
---|
152 | choices of formal parameter names. |
---|
153 | |
---|
154 | * You might also want to correct some of the indentation by hand and |
---|
155 | break long lines. (The conversion programs don't write lines |
---|
156 | longer than eighty characters in any case.) |
---|
157 | |
---|
158 | |
---|
159 | File: gcc.info, Node: Non-bugs, Next: Warnings and Errors, Prev: Protoize Caveats, Up: Trouble |
---|
160 | |
---|
161 | Certain Changes We Don't Want to Make |
---|
162 | ===================================== |
---|
163 | |
---|
164 | This section lists changes that people frequently request, but which |
---|
165 | we do not make because we think GNU CC is better without them. |
---|
166 | |
---|
167 | * Checking the number and type of arguments to a function which has |
---|
168 | an old-fashioned definition and no prototype. |
---|
169 | |
---|
170 | Such a feature would work only occasionally--only for calls that |
---|
171 | appear in the same file as the called function, following the |
---|
172 | definition. The only way to check all calls reliably is to add a |
---|
173 | prototype for the function. But adding a prototype eliminates the |
---|
174 | motivation for this feature. So the feature is not worthwhile. |
---|
175 | |
---|
176 | * Warning about using an expression whose type is signed as a shift |
---|
177 | count. |
---|
178 | |
---|
179 | Shift count operands are probably signed more often than unsigned. |
---|
180 | Warning about this would cause far more annoyance than good. |
---|
181 | |
---|
182 | * Warning about assigning a signed value to an unsigned variable. |
---|
183 | |
---|
184 | Such assignments must be very common; warning about them would |
---|
185 | cause more annoyance than good. |
---|
186 | |
---|
187 | * Warning about unreachable code. |
---|
188 | |
---|
189 | It's very common to have unreachable code in machine-generated |
---|
190 | programs. For example, this happens normally in some files of GNU |
---|
191 | C itself. |
---|
192 | |
---|
193 | * Warning when a non-void function value is ignored. |
---|
194 | |
---|
195 | Coming as I do from a Lisp background, I balk at the idea that |
---|
196 | there is something dangerous about discarding a value. There are |
---|
197 | functions that return values which some callers may find useful; |
---|
198 | it makes no sense to clutter the program with a cast to `void' |
---|
199 | whenever the value isn't useful. |
---|
200 | |
---|
201 | * Assuming (for optimization) that the address of an external symbol |
---|
202 | is never zero. |
---|
203 | |
---|
204 | This assumption is false on certain systems when `#pragma weak' is |
---|
205 | used. |
---|
206 | |
---|
207 | * Making `-fshort-enums' the default. |
---|
208 | |
---|
209 | This would cause storage layout to be incompatible with most other |
---|
210 | C compilers. And it doesn't seem very important, given that you |
---|
211 | can get the same result in other ways. The case where it matters |
---|
212 | most is when the enumeration-valued object is inside a structure, |
---|
213 | and in that case you can specify a field width explicitly. |
---|
214 | |
---|
215 | * Making bitfields unsigned by default on particular machines where |
---|
216 | "the ABI standard" says to do so. |
---|
217 | |
---|
218 | The ANSI C standard leaves it up to the implementation whether a |
---|
219 | bitfield declared plain `int' is signed or not. This in effect |
---|
220 | creates two alternative dialects of C. |
---|
221 | |
---|
222 | The GNU C compiler supports both dialects; you can specify the |
---|
223 | signed dialect with `-fsigned-bitfields' and the unsigned dialect |
---|
224 | with `-funsigned-bitfields'. However, this leaves open the |
---|
225 | question of which dialect to use by default. |
---|
226 | |
---|
227 | Currently, the preferred dialect makes plain bitfields signed, |
---|
228 | because this is simplest. Since `int' is the same as `signed int' |
---|
229 | in every other context, it is cleanest for them to be the same in |
---|
230 | bitfields as well. |
---|
231 | |
---|
232 | Some computer manufacturers have published Application Binary |
---|
233 | Interface standards which specify that plain bitfields should be |
---|
234 | unsigned. It is a mistake, however, to say anything about this |
---|
235 | issue in an ABI. This is because the handling of plain bitfields |
---|
236 | distinguishes two dialects of C. Both dialects are meaningful on |
---|
237 | every type of machine. Whether a particular object file was |
---|
238 | compiled using signed bitfields or unsigned is of no concern to |
---|
239 | other object files, even if they access the same bitfields in the |
---|
240 | same data structures. |
---|
241 | |
---|
242 | A given program is written in one or the other of these two |
---|
243 | dialects. The program stands a chance to work on most any machine |
---|
244 | if it is compiled with the proper dialect. It is unlikely to work |
---|
245 | at all if compiled with the wrong dialect. |
---|
246 | |
---|
247 | Many users appreciate the GNU C compiler because it provides an |
---|
248 | environment that is uniform across machines. These users would be |
---|
249 | inconvenienced if the compiler treated plain bitfields differently |
---|
250 | on certain machines. |
---|
251 | |
---|
252 | Occasionally users write programs intended only for a particular |
---|
253 | machine type. On these occasions, the users would benefit if the |
---|
254 | GNU C compiler were to support by default the same dialect as the |
---|
255 | other compilers on that machine. But such applications are rare. |
---|
256 | And users writing a program to run on more than one type of |
---|
257 | machine cannot possibly benefit from this kind of compatibility. |
---|
258 | |
---|
259 | This is why GNU CC does and will treat plain bitfields in the same |
---|
260 | fashion on all types of machines (by default). |
---|
261 | |
---|
262 | There are some arguments for making bitfields unsigned by default |
---|
263 | on all machines. If, for example, this becomes a universal de |
---|
264 | facto standard, it would make sense for GNU CC to go along with |
---|
265 | it. This is something to be considered in the future. |
---|
266 | |
---|
267 | (Of course, users strongly concerned about portability should |
---|
268 | indicate explicitly in each bitfield whether it is signed or not. |
---|
269 | In this way, they write programs which have the same meaning in |
---|
270 | both C dialects.) |
---|
271 | |
---|
272 | * Undefining `__STDC__' when `-ansi' is not used. |
---|
273 | |
---|
274 | Currently, GNU CC defines `__STDC__' as long as you don't use |
---|
275 | `-traditional'. This provides good results in practice. |
---|
276 | |
---|
277 | Programmers normally use conditionals on `__STDC__' to ask whether |
---|
278 | it is safe to use certain features of ANSI C, such as function |
---|
279 | prototypes or ANSI token concatenation. Since plain `gcc' supports |
---|
280 | all the features of ANSI C, the correct answer to these questions |
---|
281 | is "yes". |
---|
282 | |
---|
283 | Some users try to use `__STDC__' to check for the availability of |
---|
284 | certain library facilities. This is actually incorrect usage in |
---|
285 | an ANSI C program, because the ANSI C standard says that a |
---|
286 | conforming freestanding implementation should define `__STDC__' |
---|
287 | even though it does not have the library facilities. `gcc -ansi |
---|
288 | -pedantic' is a conforming freestanding implementation, and it is |
---|
289 | therefore required to define `__STDC__', even though it does not |
---|
290 | come with an ANSI C library. |
---|
291 | |
---|
292 | Sometimes people say that defining `__STDC__' in a compiler that |
---|
293 | does not completely conform to the ANSI C standard somehow |
---|
294 | violates the standard. This is illogical. The standard is a |
---|
295 | standard for compilers that claim to support ANSI C, such as `gcc |
---|
296 | -ansi'--not for other compilers such as plain `gcc'. Whatever the |
---|
297 | ANSI C standard says is relevant to the design of plain `gcc' |
---|
298 | without `-ansi' only for pragmatic reasons, not as a requirement. |
---|
299 | |
---|
300 | * Undefining `__STDC__' in C++. |
---|
301 | |
---|
302 | Programs written to compile with C++-to-C translators get the |
---|
303 | value of `__STDC__' that goes with the C compiler that is |
---|
304 | subsequently used. These programs must test `__STDC__' to |
---|
305 | determine what kind of C preprocessor that compiler uses: whether |
---|
306 | they should concatenate tokens in the ANSI C fashion or in the |
---|
307 | traditional fashion. |
---|
308 | |
---|
309 | These programs work properly with GNU C++ if `__STDC__' is defined. |
---|
310 | They would not work otherwise. |
---|
311 | |
---|
312 | In addition, many header files are written to provide prototypes |
---|
313 | in ANSI C but not in traditional C. Many of these header files |
---|
314 | can work without change in C++ provided `__STDC__' is defined. If |
---|
315 | `__STDC__' is not defined, they will all fail, and will all need |
---|
316 | to be changed to test explicitly for C++ as well. |
---|
317 | |
---|
318 | * Deleting "empty" loops. |
---|
319 | |
---|
320 | GNU CC does not delete "empty" loops because the most likely reason |
---|
321 | you would put one in a program is to have a delay. Deleting them |
---|
322 | will not make real programs run any faster, so it would be |
---|
323 | pointless. |
---|
324 | |
---|
325 | It would be different if optimization of a nonempty loop could |
---|
326 | produce an empty one. But this generally can't happen. |
---|
327 | |
---|
328 | * Making side effects happen in the same order as in some other |
---|
329 | compiler. |
---|
330 | |
---|
331 | It is never safe to depend on the order of evaluation of side |
---|
332 | effects. For example, a function call like this may very well |
---|
333 | behave differently from one compiler to another: |
---|
334 | |
---|
335 | void func (int, int); |
---|
336 | |
---|
337 | int i = 2; |
---|
338 | func (i++, i++); |
---|
339 | |
---|
340 | There is no guarantee (in either the C or the C++ standard language |
---|
341 | definitions) that the increments will be evaluated in any |
---|
342 | particular order. Either increment might happen first. `func' |
---|
343 | might get the arguments `2, 3', or it might get `3, 2', or even |
---|
344 | `2, 2'. |
---|
345 | |
---|
346 | * Not allowing structures with volatile fields in registers. |
---|
347 | |
---|
348 | Strictly speaking, there is no prohibition in the ANSI C standard |
---|
349 | against allowing structures with volatile fields in registers, but |
---|
350 | it does not seem to make any sense and is probably not what you |
---|
351 | wanted to do. So the compiler will give an error message in this |
---|
352 | case. |
---|
353 | |
---|
354 | |
---|
355 | File: gcc.info, Node: Warnings and Errors, Prev: Non-bugs, Up: Trouble |
---|
356 | |
---|
357 | Warning Messages and Error Messages |
---|
358 | =================================== |
---|
359 | |
---|
360 | The GNU compiler can produce two kinds of diagnostics: errors and |
---|
361 | warnings. Each kind has a different purpose: |
---|
362 | |
---|
363 | *Errors* report problems that make it impossible to compile your |
---|
364 | program. GNU CC reports errors with the source file name and line |
---|
365 | number where the problem is apparent. |
---|
366 | |
---|
367 | *Warnings* report other unusual conditions in your code that *may* |
---|
368 | indicate a problem, although compilation can (and does) proceed. |
---|
369 | Warning messages also report the source file name and line number, |
---|
370 | but include the text `warning:' to distinguish them from error |
---|
371 | messages. |
---|
372 | |
---|
373 | Warnings may indicate danger points where you should check to make |
---|
374 | sure that your program really does what you intend; or the use of |
---|
375 | obsolete features; or the use of nonstandard features of GNU C or C++. |
---|
376 | Many warnings are issued only if you ask for them, with one of the `-W' |
---|
377 | options (for instance, `-Wall' requests a variety of useful warnings). |
---|
378 | |
---|
379 | GNU CC always tries to compile your program if possible; it never |
---|
380 | gratuitously rejects a program whose meaning is clear merely because |
---|
381 | (for instance) it fails to conform to a standard. In some cases, |
---|
382 | however, the C and C++ standards specify that certain extensions are |
---|
383 | forbidden, and a diagnostic *must* be issued by a conforming compiler. |
---|
384 | The `-pedantic' option tells GNU CC to issue warnings in such cases; |
---|
385 | `-pedantic-errors' says to make them errors instead. This does not |
---|
386 | mean that *all* non-ANSI constructs get warnings or errors. |
---|
387 | |
---|
388 | *Note Options to Request or Suppress Warnings: Warning Options, for |
---|
389 | more detail on these and related command-line options. |
---|
390 | |
---|
391 | |
---|
392 | File: gcc.info, Node: Bugs, Next: Service, Prev: Trouble, Up: Top |
---|
393 | |
---|
394 | Reporting Bugs |
---|
395 | ************** |
---|
396 | |
---|
397 | Your bug reports play an essential role in making GNU CC reliable. |
---|
398 | |
---|
399 | When you encounter a problem, the first thing to do is to see if it |
---|
400 | is already known. *Note Trouble::. If it isn't known, then you should |
---|
401 | report the problem. |
---|
402 | |
---|
403 | Reporting a bug may help you by bringing a solution to your problem, |
---|
404 | or it may not. (If it does not, look in the service directory; see |
---|
405 | *Note Service::.) In any case, the principal function of a bug report |
---|
406 | is to help the entire community by making the next version of GNU CC |
---|
407 | work better. Bug reports are your contribution to the maintenance of |
---|
408 | GNU CC. |
---|
409 | |
---|
410 | Since the maintainers are very overloaded, we cannot respond to every |
---|
411 | bug report. However, if the bug has not been fixed, we are likely to |
---|
412 | send you a patch and ask you to tell us whether it works. |
---|
413 | |
---|
414 | In order for a bug report to serve its purpose, you must include the |
---|
415 | information that makes for fixing the bug. |
---|
416 | |
---|
417 | * Menu: |
---|
418 | |
---|
419 | * Criteria: Bug Criteria. Have you really found a bug? |
---|
420 | * Where: Bug Lists. Where to send your bug report. |
---|
421 | * Reporting: Bug Reporting. How to report a bug effectively. |
---|
422 | * Patches: Sending Patches. How to send a patch for GNU CC. |
---|
423 | * Known: Trouble. Known problems. |
---|
424 | * Help: Service. Where to ask for help. |
---|
425 | |
---|
426 | |
---|
427 | File: gcc.info, Node: Bug Criteria, Next: Bug Lists, Up: Bugs |
---|
428 | |
---|
429 | Have You Found a Bug? |
---|
430 | ===================== |
---|
431 | |
---|
432 | If you are not sure whether you have found a bug, here are some |
---|
433 | guidelines: |
---|
434 | |
---|
435 | * If the compiler gets a fatal signal, for any input whatever, that |
---|
436 | is a compiler bug. Reliable compilers never crash. |
---|
437 | |
---|
438 | * If the compiler produces invalid assembly code, for any input |
---|
439 | whatever (except an `asm' statement), that is a compiler bug, |
---|
440 | unless the compiler reports errors (not just warnings) which would |
---|
441 | ordinarily prevent the assembler from being run. |
---|
442 | |
---|
443 | * If the compiler produces valid assembly code that does not |
---|
444 | correctly execute the input source code, that is a compiler bug. |
---|
445 | |
---|
446 | However, you must double-check to make sure, because you may have |
---|
447 | run into an incompatibility between GNU C and traditional C (*note |
---|
448 | Incompatibilities::.). These incompatibilities might be considered |
---|
449 | bugs, but they are inescapable consequences of valuable features. |
---|
450 | |
---|
451 | Or you may have a program whose behavior is undefined, which |
---|
452 | happened by chance to give the desired results with another C or |
---|
453 | C++ compiler. |
---|
454 | |
---|
455 | For example, in many nonoptimizing compilers, you can write `x;' |
---|
456 | at the end of a function instead of `return x;', with the same |
---|
457 | results. But the value of the function is undefined if `return' |
---|
458 | is omitted; it is not a bug when GNU CC produces different results. |
---|
459 | |
---|
460 | Problems often result from expressions with two increment |
---|
461 | operators, as in `f (*p++, *p++)'. Your previous compiler might |
---|
462 | have interpreted that expression the way you intended; GNU CC might |
---|
463 | interpret it another way. Neither compiler is wrong. The bug is |
---|
464 | in your code. |
---|
465 | |
---|
466 | After you have localized the error to a single source line, it |
---|
467 | should be easy to check for these things. If your program is |
---|
468 | correct and well defined, you have found a compiler bug. |
---|
469 | |
---|
470 | * If the compiler produces an error message for valid input, that is |
---|
471 | a compiler bug. |
---|
472 | |
---|
473 | * If the compiler does not produce an error message for invalid |
---|
474 | input, that is a compiler bug. However, you should note that your |
---|
475 | idea of "invalid input" might be my idea of "an extension" or |
---|
476 | "support for traditional practice". |
---|
477 | |
---|
478 | * If you are an experienced user of C or C++ compilers, your |
---|
479 | suggestions for improvement of GNU CC or GNU C++ are welcome in |
---|
480 | any case. |
---|
481 | |
---|
482 | |
---|
483 | File: gcc.info, Node: Bug Lists, Next: Bug Reporting, Prev: Bug Criteria, Up: Bugs |
---|
484 | |
---|
485 | Where to Report Bugs |
---|
486 | ==================== |
---|
487 | |
---|
488 | Send bug reports for GNU C to `bug-gcc@prep.ai.mit.edu'. |
---|
489 | |
---|
490 | Send bug reports for GNU C++ to `bug-g++@prep.ai.mit.edu'. If your |
---|
491 | bug involves the C++ class library libg++, send mail to |
---|
492 | `bug-lib-g++@prep.ai.mit.edu'. If you're not sure, you can send the |
---|
493 | bug report to both lists. |
---|
494 | |
---|
495 | *Do not send bug reports to `help-gcc@prep.ai.mit.edu' or to the |
---|
496 | newsgroup `gnu.gcc.help'.* Most users of GNU CC do not want to receive |
---|
497 | bug reports. Those that do, have asked to be on `bug-gcc' and/or |
---|
498 | `bug-g++'. |
---|
499 | |
---|
500 | The mailing lists `bug-gcc' and `bug-g++' both have newsgroups which |
---|
501 | serve as repeaters: `gnu.gcc.bug' and `gnu.g++.bug'. Each mailing list |
---|
502 | and its newsgroup carry exactly the same messages. |
---|
503 | |
---|
504 | Often people think of posting bug reports to the newsgroup instead of |
---|
505 | mailing them. This appears to work, but it has one problem which can be |
---|
506 | crucial: a newsgroup posting does not contain a mail path back to the |
---|
507 | sender. Thus, if maintainers need more information, they may be unable |
---|
508 | to reach you. For this reason, you should always send bug reports by |
---|
509 | mail to the proper mailing list. |
---|
510 | |
---|
511 | As a last resort, send bug reports on paper to: |
---|
512 | |
---|
513 | GNU Compiler Bugs |
---|
514 | Free Software Foundation |
---|
515 | 59 Temple Place - Suite 330 |
---|
516 | Boston, MA 02111-1307, USA |
---|
517 | |
---|
518 | |
---|
519 | File: gcc.info, Node: Bug Reporting, Next: Sending Patches, Prev: Bug Lists, Up: Bugs |
---|
520 | |
---|
521 | How to Report Bugs |
---|
522 | ================== |
---|
523 | |
---|
524 | The fundamental principle of reporting bugs usefully is this: |
---|
525 | *report all the facts*. If you are not sure whether to state a fact or |
---|
526 | leave it out, state it! |
---|
527 | |
---|
528 | Often people omit facts because they think they know what causes the |
---|
529 | problem and they conclude that some details don't matter. Thus, you |
---|
530 | might assume that the name of the variable you use in an example does |
---|
531 | not matter. Well, probably it doesn't, but one cannot be sure. |
---|
532 | Perhaps the bug is a stray memory reference which happens to fetch from |
---|
533 | the location where that name is stored in memory; perhaps, if the name |
---|
534 | were different, the contents of that location would fool the compiler |
---|
535 | into doing the right thing despite the bug. Play it safe and give a |
---|
536 | specific, complete example. That is the easiest thing for you to do, |
---|
537 | and the most helpful. |
---|
538 | |
---|
539 | Keep in mind that the purpose of a bug report is to enable someone to |
---|
540 | fix the bug if it is not known. It isn't very important what happens if |
---|
541 | the bug is already known. Therefore, always write your bug reports on |
---|
542 | the assumption that the bug is not known. |
---|
543 | |
---|
544 | Sometimes people give a few sketchy facts and ask, "Does this ring a |
---|
545 | bell?" This cannot help us fix a bug, so it is basically useless. We |
---|
546 | respond by asking for enough details to enable us to investigate. You |
---|
547 | might as well expedite matters by sending them to begin with. |
---|
548 | |
---|
549 | Try to make your bug report self-contained. If we have to ask you |
---|
550 | for more information, it is best if you include all the previous |
---|
551 | information in your response, as well as the information that was |
---|
552 | missing. |
---|
553 | |
---|
554 | Please report each bug in a separate message. This makes it easier |
---|
555 | for us to track which bugs have been fixed and to forward your bugs |
---|
556 | reports to the appropriate maintainer. |
---|
557 | |
---|
558 | Do not compress and encode any part of your bug report using programs |
---|
559 | such as `uuencode'. If you do so it will slow down the processing of |
---|
560 | your bug. If you must submit multiple large files, use `shar', which |
---|
561 | allows us to read your message without having to run any decompression |
---|
562 | programs. |
---|
563 | |
---|
564 | To enable someone to investigate the bug, you should include all |
---|
565 | these things: |
---|
566 | |
---|
567 | * The version of GNU CC. You can get this by running it with the |
---|
568 | `-v' option. |
---|
569 | |
---|
570 | Without this, we won't know whether there is any point in looking |
---|
571 | for the bug in the current version of GNU CC. |
---|
572 | |
---|
573 | * A complete input file that will reproduce the bug. If the bug is |
---|
574 | in the C preprocessor, send a source file and any header files |
---|
575 | that it requires. If the bug is in the compiler proper (`cc1'), |
---|
576 | run your source file through the C preprocessor by doing `gcc -E |
---|
577 | SOURCEFILE > OUTFILE', then include the contents of OUTFILE in the |
---|
578 | bug report. (When you do this, use the same `-I', `-D' or `-U' |
---|
579 | options that you used in actual compilation.) |
---|
580 | |
---|
581 | A single statement is not enough of an example. In order to |
---|
582 | compile it, it must be embedded in a complete file of compiler |
---|
583 | input; and the bug might depend on the details of how this is done. |
---|
584 | |
---|
585 | Without a real example one can compile, all anyone can do about |
---|
586 | your bug report is wish you luck. It would be futile to try to |
---|
587 | guess how to provoke the bug. For example, bugs in register |
---|
588 | allocation and reloading frequently depend on every little detail |
---|
589 | of the function they happen in. |
---|
590 | |
---|
591 | Even if the input file that fails comes from a GNU program, you |
---|
592 | should still send the complete test case. Don't ask the GNU CC |
---|
593 | maintainers to do the extra work of obtaining the program in |
---|
594 | question--they are all overworked as it is. Also, the problem may |
---|
595 | depend on what is in the header files on your system; it is |
---|
596 | unreliable for the GNU CC maintainers to try the problem with the |
---|
597 | header files available to them. By sending CPP output, you can |
---|
598 | eliminate this source of uncertainty and save us a certain |
---|
599 | percentage of wild goose chases. |
---|
600 | |
---|
601 | * The command arguments you gave GNU CC or GNU C++ to compile that |
---|
602 | example and observe the bug. For example, did you use `-O'? To |
---|
603 | guarantee you won't omit something important, list all the options. |
---|
604 | |
---|
605 | If we were to try to guess the arguments, we would probably guess |
---|
606 | wrong and then we would not encounter the bug. |
---|
607 | |
---|
608 | * The type of machine you are using, and the operating system name |
---|
609 | and version number. |
---|
610 | |
---|
611 | * The operands you gave to the `configure' command when you installed |
---|
612 | the compiler. |
---|
613 | |
---|
614 | * A complete list of any modifications you have made to the compiler |
---|
615 | source. (We don't promise to investigate the bug unless it |
---|
616 | happens in an unmodified compiler. But if you've made |
---|
617 | modifications and don't tell us, then you are sending us on a wild |
---|
618 | goose chase.) |
---|
619 | |
---|
620 | Be precise about these changes. A description in English is not |
---|
621 | enough--send a context diff for them. |
---|
622 | |
---|
623 | Adding files of your own (such as a machine description for a |
---|
624 | machine we don't support) is a modification of the compiler source. |
---|
625 | |
---|
626 | * Details of any other deviations from the standard procedure for |
---|
627 | installing GNU CC. |
---|
628 | |
---|
629 | * A description of what behavior you observe that you believe is |
---|
630 | incorrect. For example, "The compiler gets a fatal signal," or, |
---|
631 | "The assembler instruction at line 208 in the output is incorrect." |
---|
632 | |
---|
633 | Of course, if the bug is that the compiler gets a fatal signal, |
---|
634 | then one can't miss it. But if the bug is incorrect output, the |
---|
635 | maintainer might not notice unless it is glaringly wrong. None of |
---|
636 | us has time to study all the assembler code from a 50-line C |
---|
637 | program just on the chance that one instruction might be wrong. |
---|
638 | We need *you* to do this part! |
---|
639 | |
---|
640 | Even if the problem you experience is a fatal signal, you should |
---|
641 | still say so explicitly. Suppose something strange is going on, |
---|
642 | such as, your copy of the compiler is out of synch, or you have |
---|
643 | encountered a bug in the C library on your system. (This has |
---|
644 | happened!) Your copy might crash and the copy here would not. If |
---|
645 | you said to expect a crash, then when the compiler here fails to |
---|
646 | crash, we would know that the bug was not happening. If you don't |
---|
647 | say to expect a crash, then we would not know whether the bug was |
---|
648 | happening. We would not be able to draw any conclusion from our |
---|
649 | observations. |
---|
650 | |
---|
651 | If the problem is a diagnostic when compiling GNU CC with some |
---|
652 | other compiler, say whether it is a warning or an error. |
---|
653 | |
---|
654 | Often the observed symptom is incorrect output when your program |
---|
655 | is run. Sad to say, this is not enough information unless the |
---|
656 | program is short and simple. None of us has time to study a large |
---|
657 | program to figure out how it would work if compiled correctly, |
---|
658 | much less which line of it was compiled wrong. So you will have |
---|
659 | to do that. Tell us which source line it is, and what incorrect |
---|
660 | result happens when that line is executed. A person who |
---|
661 | understands the program can find this as easily as finding a bug |
---|
662 | in the program itself. |
---|
663 | |
---|
664 | * If you send examples of assembler code output from GNU CC or GNU |
---|
665 | C++, please use `-g' when you make them. The debugging information |
---|
666 | includes source line numbers which are essential for correlating |
---|
667 | the output with the input. |
---|
668 | |
---|
669 | * If you wish to mention something in the GNU CC source, refer to it |
---|
670 | by context, not by line number. |
---|
671 | |
---|
672 | The line numbers in the development sources don't match those in |
---|
673 | your sources. Your line numbers would convey no useful |
---|
674 | information to the maintainers. |
---|
675 | |
---|
676 | * Additional information from a debugger might enable someone to |
---|
677 | find a problem on a machine which he does not have available. |
---|
678 | However, you need to think when you collect this information if |
---|
679 | you want it to have any chance of being useful. |
---|
680 | |
---|
681 | For example, many people send just a backtrace, but that is never |
---|
682 | useful by itself. A simple backtrace with arguments conveys little |
---|
683 | about GNU CC because the compiler is largely data-driven; the same |
---|
684 | functions are called over and over for different RTL insns, doing |
---|
685 | different things depending on the details of the insn. |
---|
686 | |
---|
687 | Most of the arguments listed in the backtrace are useless because |
---|
688 | they are pointers to RTL list structure. The numeric values of the |
---|
689 | pointers, which the debugger prints in the backtrace, have no |
---|
690 | significance whatever; all that matters is the contents of the |
---|
691 | objects they point to (and most of the contents are other such |
---|
692 | pointers). |
---|
693 | |
---|
694 | In addition, most compiler passes consist of one or more loops that |
---|
695 | scan the RTL insn sequence. The most vital piece of information |
---|
696 | about such a loop--which insn it has reached--is usually in a |
---|
697 | local variable, not in an argument. |
---|
698 | |
---|
699 | What you need to provide in addition to a backtrace are the values |
---|
700 | of the local variables for several stack frames up. When a local |
---|
701 | variable or an argument is an RTX, first print its value and then |
---|
702 | use the GDB command `pr' to print the RTL expression that it points |
---|
703 | to. (If GDB doesn't run on your machine, use your debugger to call |
---|
704 | the function `debug_rtx' with the RTX as an argument.) In |
---|
705 | general, whenever a variable is a pointer, its value is no use |
---|
706 | without the data it points to. |
---|
707 | |
---|
708 | Here are some things that are not necessary: |
---|
709 | |
---|
710 | * A description of the envelope of the bug. |
---|
711 | |
---|
712 | Often people who encounter a bug spend a lot of time investigating |
---|
713 | which changes to the input file will make the bug go away and which |
---|
714 | changes will not affect it. |
---|
715 | |
---|
716 | This is often time consuming and not very useful, because the way |
---|
717 | we will find the bug is by running a single example under the |
---|
718 | debugger with breakpoints, not by pure deduction from a series of |
---|
719 | examples. You might as well save your time for something else. |
---|
720 | |
---|
721 | Of course, if you can find a simpler example to report *instead* of |
---|
722 | the original one, that is a convenience. Errors in the output |
---|
723 | will be easier to spot, running under the debugger will take less |
---|
724 | time, etc. Most GNU CC bugs involve just one function, so the |
---|
725 | most straightforward way to simplify an example is to delete all |
---|
726 | the function definitions except the one where the bug occurs. |
---|
727 | Those earlier in the file may be replaced by external declarations |
---|
728 | if the crucial function depends on them. (Exception: inline |
---|
729 | functions may affect compilation of functions defined later in the |
---|
730 | file.) |
---|
731 | |
---|
732 | However, simplification is not vital; if you don't want to do this, |
---|
733 | report the bug anyway and send the entire test case you used. |
---|
734 | |
---|
735 | * In particular, some people insert conditionals `#ifdef BUG' around |
---|
736 | a statement which, if removed, makes the bug not happen. These |
---|
737 | are just clutter; we won't pay any attention to them anyway. |
---|
738 | Besides, you should send us cpp output, and that can't have |
---|
739 | conditionals. |
---|
740 | |
---|
741 | * A patch for the bug. |
---|
742 | |
---|
743 | A patch for the bug is useful if it is a good one. But don't omit |
---|
744 | the necessary information, such as the test case, on the |
---|
745 | assumption that a patch is all we need. We might see problems |
---|
746 | with your patch and decide to fix the problem another way, or we |
---|
747 | might not understand it at all. |
---|
748 | |
---|
749 | Sometimes with a program as complicated as GNU CC it is very hard |
---|
750 | to construct an example that will make the program follow a |
---|
751 | certain path through the code. If you don't send the example, we |
---|
752 | won't be able to construct one, so we won't be able to verify that |
---|
753 | the bug is fixed. |
---|
754 | |
---|
755 | And if we can't understand what bug you are trying to fix, or why |
---|
756 | your patch should be an improvement, we won't install it. A test |
---|
757 | case will help us to understand. |
---|
758 | |
---|
759 | *Note Sending Patches::, for guidelines on how to make it easy for |
---|
760 | us to understand and install your patches. |
---|
761 | |
---|
762 | * A guess about what the bug is or what it depends on. |
---|
763 | |
---|
764 | Such guesses are usually wrong. Even I can't guess right about |
---|
765 | such things without first using the debugger to find the facts. |
---|
766 | |
---|
767 | * A core dump file. |
---|
768 | |
---|
769 | We have no way of examining a core dump for your type of machine |
---|
770 | unless we have an identical system--and if we do have one, we |
---|
771 | should be able to reproduce the crash ourselves. |
---|
772 | |
---|
773 | |
---|
774 | File: gcc.info, Node: Sending Patches, Prev: Bug Reporting, Up: Bugs |
---|
775 | |
---|
776 | Sending Patches for GNU CC |
---|
777 | ========================== |
---|
778 | |
---|
779 | If you would like to write bug fixes or improvements for the GNU C |
---|
780 | compiler, that is very helpful. Send suggested fixes to the bug report |
---|
781 | mailing list, `bug-gcc@prep.ai.mit.edu'. |
---|
782 | |
---|
783 | Please follow these guidelines so we can study your patches |
---|
784 | efficiently. If you don't follow these guidelines, your information |
---|
785 | might still be useful, but using it will take extra work. Maintaining |
---|
786 | GNU C is a lot of work in the best of circumstances, and we can't keep |
---|
787 | up unless you do your best to help. |
---|
788 | |
---|
789 | * Send an explanation with your changes of what problem they fix or |
---|
790 | what improvement they bring about. For a bug fix, just include a |
---|
791 | copy of the bug report, and explain why the change fixes the bug. |
---|
792 | |
---|
793 | (Referring to a bug report is not as good as including it, because |
---|
794 | then we will have to look it up, and we have probably already |
---|
795 | deleted it if we've already fixed the bug.) |
---|
796 | |
---|
797 | * Always include a proper bug report for the problem you think you |
---|
798 | have fixed. We need to convince ourselves that the change is |
---|
799 | right before installing it. Even if it is right, we might have |
---|
800 | trouble judging it if we don't have a way to reproduce the problem. |
---|
801 | |
---|
802 | * Include all the comments that are appropriate to help people |
---|
803 | reading the source in the future understand why this change was |
---|
804 | needed. |
---|
805 | |
---|
806 | * Don't mix together changes made for different reasons. Send them |
---|
807 | *individually*. |
---|
808 | |
---|
809 | If you make two changes for separate reasons, then we might not |
---|
810 | want to install them both. We might want to install just one. If |
---|
811 | you send them all jumbled together in a single set of diffs, we |
---|
812 | have to do extra work to disentangle them--to figure out which |
---|
813 | parts of the change serve which purpose. If we don't have time |
---|
814 | for this, we might have to ignore your changes entirely. |
---|
815 | |
---|
816 | If you send each change as soon as you have written it, with its |
---|
817 | own explanation, then the two changes never get tangled up, and we |
---|
818 | can consider each one properly without any extra work to |
---|
819 | disentangle them. |
---|
820 | |
---|
821 | Ideally, each change you send should be impossible to subdivide |
---|
822 | into parts that we might want to consider separately, because each |
---|
823 | of its parts gets its motivation from the other parts. |
---|
824 | |
---|
825 | * Send each change as soon as that change is finished. Sometimes |
---|
826 | people think they are helping us by accumulating many changes to |
---|
827 | send them all together. As explained above, this is absolutely |
---|
828 | the worst thing you could do. |
---|
829 | |
---|
830 | Since you should send each change separately, you might as well |
---|
831 | send it right away. That gives us the option of installing it |
---|
832 | immediately if it is important. |
---|
833 | |
---|
834 | * Use `diff -c' to make your diffs. Diffs without context are hard |
---|
835 | for us to install reliably. More than that, they make it hard for |
---|
836 | us to study the diffs to decide whether we want to install them. |
---|
837 | Unidiff format is better than contextless diffs, but not as easy |
---|
838 | to read as `-c' format. |
---|
839 | |
---|
840 | If you have GNU diff, use `diff -cp', which shows the name of the |
---|
841 | function that each change occurs in. |
---|
842 | |
---|
843 | * Write the change log entries for your changes. We get lots of |
---|
844 | changes, and we don't have time to do all the change log writing |
---|
845 | ourselves. |
---|
846 | |
---|
847 | Read the `ChangeLog' file to see what sorts of information to put |
---|
848 | in, and to learn the style that we use. The purpose of the change |
---|
849 | log is to show people where to find what was changed. So you need |
---|
850 | to be specific about what functions you changed; in large |
---|
851 | functions, it's often helpful to indicate where within the |
---|
852 | function the change was. |
---|
853 | |
---|
854 | On the other hand, once you have shown people where to find the |
---|
855 | change, you need not explain its purpose. Thus, if you add a new |
---|
856 | function, all you need to say about it is that it is new. If you |
---|
857 | feel that the purpose needs explaining, it probably does--but the |
---|
858 | explanation will be much more useful if you put it in comments in |
---|
859 | the code. |
---|
860 | |
---|
861 | If you would like your name to appear in the header line for who |
---|
862 | made the change, send us the header line. |
---|
863 | |
---|
864 | * When you write the fix, keep in mind that we can't install a |
---|
865 | change that would break other systems. |
---|
866 | |
---|
867 | People often suggest fixing a problem by changing |
---|
868 | machine-independent files such as `toplev.c' to do something |
---|
869 | special that a particular system needs. Sometimes it is totally |
---|
870 | obvious that such changes would break GNU CC for almost all users. |
---|
871 | We can't possibly make a change like that. At best it might tell |
---|
872 | us how to write another patch that would solve the problem |
---|
873 | acceptably. |
---|
874 | |
---|
875 | Sometimes people send fixes that *might* be an improvement in |
---|
876 | general--but it is hard to be sure of this. It's hard to install |
---|
877 | such changes because we have to study them very carefully. Of |
---|
878 | course, a good explanation of the reasoning by which you concluded |
---|
879 | the change was correct can help convince us. |
---|
880 | |
---|
881 | The safest changes are changes to the configuration files for a |
---|
882 | particular machine. These are safe because they can't create new |
---|
883 | bugs on other machines. |
---|
884 | |
---|
885 | Please help us keep up with the workload by designing the patch in |
---|
886 | a form that is good to install. |
---|
887 | |
---|
888 | |
---|
889 | File: gcc.info, Node: Service, Next: VMS, Prev: Bugs, Up: Top |
---|
890 | |
---|
891 | How To Get Help with GNU CC |
---|
892 | *************************** |
---|
893 | |
---|
894 | If you need help installing, using or changing GNU CC, there are two |
---|
895 | ways to find it: |
---|
896 | |
---|
897 | * Send a message to a suitable network mailing list. First try |
---|
898 | `bug-gcc@prep.ai.mit.edu', and if that brings no response, try |
---|
899 | `help-gcc@prep.ai.mit.edu'. |
---|
900 | |
---|
901 | * Look in the service directory for someone who might help you for a |
---|
902 | fee. The service directory is found in the file named `SERVICE' |
---|
903 | in the GNU CC distribution. |
---|
904 | |
---|
905 | |
---|
906 | File: gcc.info, Node: VMS, Next: Portability, Prev: Service, Up: Top |
---|
907 | |
---|
908 | Using GNU CC on VMS |
---|
909 | ******************* |
---|
910 | |
---|
911 | Here is how to use GNU CC on VMS. |
---|
912 | |
---|
913 | * Menu: |
---|
914 | |
---|
915 | * Include Files and VMS:: Where the preprocessor looks for the include files. |
---|
916 | * Global Declarations:: How to do globaldef, globalref and globalvalue with |
---|
917 | GNU CC. |
---|
918 | * VMS Misc:: Misc information. |
---|
919 | |
---|
920 | |
---|
921 | File: gcc.info, Node: Include Files and VMS, Next: Global Declarations, Up: VMS |
---|
922 | |
---|
923 | Include Files and VMS |
---|
924 | ===================== |
---|
925 | |
---|
926 | Due to the differences between the filesystems of Unix and VMS, GNU |
---|
927 | CC attempts to translate file names in `#include' into names that VMS |
---|
928 | will understand. The basic strategy is to prepend a prefix to the |
---|
929 | specification of the include file, convert the whole filename to a VMS |
---|
930 | filename, and then try to open the file. GNU CC tries various prefixes |
---|
931 | one by one until one of them succeeds: |
---|
932 | |
---|
933 | 1. The first prefix is the `GNU_CC_INCLUDE:' logical name: this is |
---|
934 | where GNU C header files are traditionally stored. If you wish to |
---|
935 | store header files in non-standard locations, then you can assign |
---|
936 | the logical `GNU_CC_INCLUDE' to be a search list, where each |
---|
937 | element of the list is suitable for use with a rooted logical. |
---|
938 | |
---|
939 | 2. The next prefix tried is `SYS$SYSROOT:[SYSLIB.]'. This is where |
---|
940 | VAX-C header files are traditionally stored. |
---|
941 | |
---|
942 | 3. If the include file specification by itself is a valid VMS |
---|
943 | filename, the preprocessor then uses this name with no prefix in |
---|
944 | an attempt to open the include file. |
---|
945 | |
---|
946 | 4. If the file specification is not a valid VMS filename (i.e. does |
---|
947 | not contain a device or a directory specifier, and contains a `/' |
---|
948 | character), the preprocessor tries to convert it from Unix syntax |
---|
949 | to VMS syntax. |
---|
950 | |
---|
951 | Conversion works like this: the first directory name becomes a |
---|
952 | device, and the rest of the directories are converted into |
---|
953 | VMS-format directory names. For example, the name `X11/foobar.h' |
---|
954 | is translated to `X11:[000000]foobar.h' or `X11:foobar.h', |
---|
955 | whichever one can be opened. This strategy allows you to assign a |
---|
956 | logical name to point to the actual location of the header files. |
---|
957 | |
---|
958 | 5. If none of these strategies succeeds, the `#include' fails. |
---|
959 | |
---|
960 | Include directives of the form: |
---|
961 | |
---|
962 | #include foobar |
---|
963 | |
---|
964 | are a common source of incompatibility between VAX-C and GNU CC. VAX-C |
---|
965 | treats this much like a standard `#include <foobar.h>' directive. That |
---|
966 | is incompatible with the ANSI C behavior implemented by GNU CC: to |
---|
967 | expand the name `foobar' as a macro. Macro expansion should eventually |
---|
968 | yield one of the two standard formats for `#include': |
---|
969 | |
---|
970 | #include "FILE" |
---|
971 | #include <FILE> |
---|
972 | |
---|
973 | If you have this problem, the best solution is to modify the source |
---|
974 | to convert the `#include' directives to one of the two standard forms. |
---|
975 | That will work with either compiler. If you want a quick and dirty fix, |
---|
976 | define the file names as macros with the proper expansion, like this: |
---|
977 | |
---|
978 | #define stdio <stdio.h> |
---|
979 | |
---|
980 | This will work, as long as the name doesn't conflict with anything else |
---|
981 | in the program. |
---|
982 | |
---|
983 | Another source of incompatibility is that VAX-C assumes that: |
---|
984 | |
---|
985 | #include "foobar" |
---|
986 | |
---|
987 | is actually asking for the file `foobar.h'. GNU CC does not make this |
---|
988 | assumption, and instead takes what you ask for literally; it tries to |
---|
989 | read the file `foobar'. The best way to avoid this problem is to |
---|
990 | always specify the desired file extension in your include directives. |
---|
991 | |
---|
992 | GNU CC for VMS is distributed with a set of include files that is |
---|
993 | sufficient to compile most general purpose programs. Even though the |
---|
994 | GNU CC distribution does not contain header files to define constants |
---|
995 | and structures for some VMS system-specific functions, there is no |
---|
996 | reason why you cannot use GNU CC with any of these functions. You first |
---|
997 | may have to generate or create header files, either by using the public |
---|
998 | domain utility `UNSDL' (which can be found on a DECUS tape), or by |
---|
999 | extracting the relevant modules from one of the system macro libraries, |
---|
1000 | and using an editor to construct a C header file. |
---|
1001 | |
---|
1002 | A `#include' file name cannot contain a DECNET node name. The |
---|
1003 | preprocessor reports an I/O error if you attempt to use a node name, |
---|
1004 | whether explicitly, or implicitly via a logical name. |
---|
1005 | |
---|
1006 | |
---|
1007 | File: gcc.info, Node: Global Declarations, Next: VMS Misc, Prev: Include Files and VMS, Up: VMS |
---|
1008 | |
---|
1009 | Global Declarations and VMS |
---|
1010 | =========================== |
---|
1011 | |
---|
1012 | GNU CC does not provide the `globalref', `globaldef' and |
---|
1013 | `globalvalue' keywords of VAX-C. You can get the same effect with an |
---|
1014 | obscure feature of GAS, the GNU assembler. (This requires GAS version |
---|
1015 | 1.39 or later.) The following macros allow you to use this feature in |
---|
1016 | a fairly natural way: |
---|
1017 | |
---|
1018 | #ifdef __GNUC__ |
---|
1019 | #define GLOBALREF(TYPE,NAME) \ |
---|
1020 | TYPE NAME \ |
---|
1021 | asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME) |
---|
1022 | #define GLOBALDEF(TYPE,NAME,VALUE) \ |
---|
1023 | TYPE NAME \ |
---|
1024 | asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME) \ |
---|
1025 | = VALUE |
---|
1026 | #define GLOBALVALUEREF(TYPE,NAME) \ |
---|
1027 | const TYPE NAME[1] \ |
---|
1028 | asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME) |
---|
1029 | #define GLOBALVALUEDEF(TYPE,NAME,VALUE) \ |
---|
1030 | const TYPE NAME[1] \ |
---|
1031 | asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME) \ |
---|
1032 | = {VALUE} |
---|
1033 | #else |
---|
1034 | #define GLOBALREF(TYPE,NAME) \ |
---|
1035 | globalref TYPE NAME |
---|
1036 | #define GLOBALDEF(TYPE,NAME,VALUE) \ |
---|
1037 | globaldef TYPE NAME = VALUE |
---|
1038 | #define GLOBALVALUEDEF(TYPE,NAME,VALUE) \ |
---|
1039 | globalvalue TYPE NAME = VALUE |
---|
1040 | #define GLOBALVALUEREF(TYPE,NAME) \ |
---|
1041 | globalvalue TYPE NAME |
---|
1042 | #endif |
---|
1043 | |
---|
1044 | (The `_$$PsectAttributes_GLOBALSYMBOL' prefix at the start of the name |
---|
1045 | is removed by the assembler, after it has modified the attributes of |
---|
1046 | the symbol). These macros are provided in the VMS binaries |
---|
1047 | distribution in a header file `GNU_HACKS.H'. An example of the usage |
---|
1048 | is: |
---|
1049 | |
---|
1050 | GLOBALREF (int, ijk); |
---|
1051 | GLOBALDEF (int, jkl, 0); |
---|
1052 | |
---|
1053 | The macros `GLOBALREF' and `GLOBALDEF' cannot be used |
---|
1054 | straightforwardly for arrays, since there is no way to insert the array |
---|
1055 | dimension into the declaration at the right place. However, you can |
---|
1056 | declare an array with these macros if you first define a typedef for the |
---|
1057 | array type, like this: |
---|
1058 | |
---|
1059 | typedef int intvector[10]; |
---|
1060 | GLOBALREF (intvector, foo); |
---|
1061 | |
---|
1062 | Array and structure initializers will also break the macros; you can |
---|
1063 | define the initializer to be a macro of its own, or you can expand the |
---|
1064 | `GLOBALDEF' macro by hand. You may find a case where you wish to use |
---|
1065 | the `GLOBALDEF' macro with a large array, but you are not interested in |
---|
1066 | explicitly initializing each element of the array. In such cases you |
---|
1067 | can use an initializer like: `{0,}', which will initialize the entire |
---|
1068 | array to `0'. |
---|
1069 | |
---|
1070 | A shortcoming of this implementation is that a variable declared with |
---|
1071 | `GLOBALVALUEREF' or `GLOBALVALUEDEF' is always an array. For example, |
---|
1072 | the declaration: |
---|
1073 | |
---|
1074 | GLOBALVALUEREF(int, ijk); |
---|
1075 | |
---|
1076 | declares the variable `ijk' as an array of type `int [1]'. This is |
---|
1077 | done because a globalvalue is actually a constant; its "value" is what |
---|
1078 | the linker would normally consider an address. That is not how an |
---|
1079 | integer value works in C, but it is how an array works. So treating |
---|
1080 | the symbol as an array name gives consistent results--with the |
---|
1081 | exception that the value seems to have the wrong type. *Don't try to |
---|
1082 | access an element of the array.* It doesn't have any elements. The |
---|
1083 | array "address" may not be the address of actual storage. |
---|
1084 | |
---|
1085 | The fact that the symbol is an array may lead to warnings where the |
---|
1086 | variable is used. Insert type casts to avoid the warnings. Here is an |
---|
1087 | example; it takes advantage of the ANSI C feature allowing macros that |
---|
1088 | expand to use the same name as the macro itself. |
---|
1089 | |
---|
1090 | GLOBALVALUEREF (int, ss$_normal); |
---|
1091 | GLOBALVALUEDEF (int, xyzzy,123); |
---|
1092 | #ifdef __GNUC__ |
---|
1093 | #define ss$_normal ((int) ss$_normal) |
---|
1094 | #define xyzzy ((int) xyzzy) |
---|
1095 | #endif |
---|
1096 | |
---|
1097 | Don't use `globaldef' or `globalref' with a variable whose type is |
---|
1098 | an enumeration type; this is not implemented. Instead, make the |
---|
1099 | variable an integer, and use a `globalvaluedef' for each of the |
---|
1100 | enumeration values. An example of this would be: |
---|
1101 | |
---|
1102 | #ifdef __GNUC__ |
---|
1103 | GLOBALDEF (int, color, 0); |
---|
1104 | GLOBALVALUEDEF (int, RED, 0); |
---|
1105 | GLOBALVALUEDEF (int, BLUE, 1); |
---|
1106 | GLOBALVALUEDEF (int, GREEN, 3); |
---|
1107 | #else |
---|
1108 | enum globaldef color {RED, BLUE, GREEN = 3}; |
---|
1109 | #endif |
---|
1110 | |
---|