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1.1 ! root 1: This is Info file gcc.info, produced by Makeinfo-1.54 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 675 Massachusetts Avenue ! 7: Cambridge, MA 02139 USA ! 8: ! 9: Copyright (C) 1988, 1989, 1992, 1993 Free Software Foundation, Inc. ! 10: ! 11: Permission is granted to make and distribute verbatim copies of this ! 12: manual provided the copyright notice and this permission notice are ! 13: preserved on all copies. ! 14: ! 15: Permission is granted to copy and distribute modified versions of ! 16: this manual under the conditions for verbatim copying, provided also ! 17: that the sections entitled "GNU General Public License" and "Protect ! 18: Your Freedom--Fight `Look And Feel'" are included exactly as in the ! 19: original, and provided that the entire resulting derived work is ! 20: distributed under the terms of a permission notice identical to this ! 21: one. ! 22: ! 23: Permission is granted to copy and distribute translations of this ! 24: manual into another language, under the above conditions for modified ! 25: versions, except that the sections entitled "GNU General Public ! 26: License" and "Protect Your Freedom--Fight `Look And Feel'", and this ! 27: permission notice, may be included in translations approved by the Free ! 28: Software Foundation instead of in the original English. ! 29: ! 30: ! 31: File: gcc.info, Node: Bug Reporting, Next: Sending Patches, Prev: Bug Lists, Up: Bugs ! 32: ! 33: How to Report Bugs ! 34: ================== ! 35: ! 36: The fundamental principle of reporting bugs usefully is this: ! 37: *report all the facts*. If you are not sure whether to state a fact or ! 38: leave it out, state it! ! 39: ! 40: Often people omit facts because they think they know what causes the ! 41: problem and they conclude that some details don't matter. Thus, you ! 42: might assume that the name of the variable you use in an example does ! 43: not matter. Well, probably it doesn't, but one cannot be sure. ! 44: Perhaps the bug is a stray memory reference which happens to fetch from ! 45: the location where that name is stored in memory; perhaps, if the name ! 46: were different, the contents of that location would fool the compiler ! 47: into doing the right thing despite the bug. Play it safe and give a ! 48: specific, complete example. That is the easiest thing for you to do, ! 49: and the most helpful. ! 50: ! 51: Keep in mind that the purpose of a bug report is to enable someone to ! 52: fix the bug if it is not known. It isn't very important what happens if ! 53: the bug is already known. Therefore, always write your bug reports on ! 54: the assumption that the bug is not known. ! 55: ! 56: Sometimes people give a few sketchy facts and ask, "Does this ring a ! 57: bell?" This cannot help us fix a bug, so it is basically useless. We ! 58: respond by asking for enough details to enable us to investigate. You ! 59: might as well expedite matters by sending them to begin with. ! 60: ! 61: Try to make your bug report self-contained. If we have to ask you ! 62: for more information, it is best if you include all the previous ! 63: information in your response, as well as the information that was ! 64: missing. ! 65: ! 66: To enable someone to investigate the bug, you should include all ! 67: these things: ! 68: ! 69: * The version of GNU CC. You can get this by running it with the ! 70: `-v' option. ! 71: ! 72: Without this, we won't know whether there is any point in looking ! 73: for the bug in the current version of GNU CC. ! 74: ! 75: * A complete input file that will reproduce the bug. If the bug is ! 76: in the C preprocessor, send a source file and any header files ! 77: that it requires. If the bug is in the compiler proper (`cc1'), ! 78: run your source file through the C preprocessor by doing `gcc -E ! 79: SOURCEFILE > OUTFILE', then include the contents of OUTFILE in the ! 80: bug report. (When you do this, use the same `-I', `-D' or `-U' ! 81: options that you used in actual compilation.) ! 82: ! 83: A single statement is not enough of an example. In order to ! 84: compile it, it must be embedded in a complete file of compiler ! 85: input; and the bug might depend on the details of how this is done. ! 86: ! 87: Without a real example one can compile, all anyone can do about ! 88: your bug report is wish you luck. It would be futile to try to ! 89: guess how to provoke the bug. For example, bugs in register ! 90: allocation and reloading frequently depend on every little detail ! 91: of the function they happen in. ! 92: ! 93: Even if the input file that fails comes from a GNU program, you ! 94: should still send the complete test case. Don't ask the GNU CC ! 95: maintainers to do the extra work of obtaining the program in ! 96: question--they are all overworked as it is. Also, the problem may ! 97: depend on what is in the header files on your system; it is ! 98: unreliable for the GNU CC maintainers to try the problem with the ! 99: header files available to them. By sending CPP output, you can ! 100: eliminate this source of uncertainty and save us a certain ! 101: percentage of wild goose chases. ! 102: ! 103: * The command arguments you gave GNU CC or GNU C++ to compile that ! 104: example and observe the bug. For example, did you use `-O'? To ! 105: guarantee you won't omit something important, list all the options. ! 106: ! 107: If we were to try to guess the arguments, we would probably guess ! 108: wrong and then we would not encounter the bug. ! 109: ! 110: * The type of machine you are using, and the operating system name ! 111: and version number. ! 112: ! 113: * The operands you gave to the `configure' command when you installed ! 114: the compiler. ! 115: ! 116: * A complete list of any modifications you have made to the compiler ! 117: source. (We don't promise to investigate the bug unless it ! 118: happens in an unmodified compiler. But if you've made ! 119: modifications and don't tell us, then you are sending us on a wild ! 120: goose chase.) ! 121: ! 122: Be precise about these changes. A description in English is not ! 123: enough--send a context diff for them. ! 124: ! 125: Adding files of your own (such as a machine description for a ! 126: machine we don't support) is a modification of the compiler source. ! 127: ! 128: * Details of any other deviations from the standard procedure for ! 129: installing GNU CC. ! 130: ! 131: * A description of what behavior you observe that you believe is ! 132: incorrect. For example, "The compiler gets a fatal signal," or, ! 133: "The assembler instruction at line 208 in the output is incorrect." ! 134: ! 135: Of course, if the bug is that the compiler gets a fatal signal, ! 136: then one can't miss it. But if the bug is incorrect output, the ! 137: maintainer might not notice unless it is glaringly wrong. None of ! 138: us has time to study all the assembler code from a 50-line C ! 139: program just on the chance that one instruction might be wrong. ! 140: We need *you* to do this part! ! 141: ! 142: Even if the problem you experience is a fatal signal, you should ! 143: still say so explicitly. Suppose something strange is going on, ! 144: such as, your copy of the compiler is out of synch, or you have ! 145: encountered a bug in the C library on your system. (This has ! 146: happened!) Your copy might crash and the copy here would not. If ! 147: you said to expect a crash, then when the compiler here fails to ! 148: crash, we would know that the bug was not happening. If you don't ! 149: say to expect a crash, then we would not know whether the bug was ! 150: happening. We would not be able to draw any conclusion from our ! 151: observations. ! 152: ! 153: If the problem is a diagnostic when compiling GNU CC with some ! 154: other compiler, say whether it is a warning or an error. ! 155: ! 156: Often the observed symptom is incorrect output when your program ! 157: is run. Sad to say, this is not enough information unless the ! 158: program is short and simple. None of us has time to study a large ! 159: program to figure out how it would work if compiled correctly, ! 160: much less which line of it was compiled wrong. So you will have ! 161: to do that. Tell us which source line it is, and what incorrect ! 162: result happens when that line is executed. A person who ! 163: understands the program can find this as easily as finding a bug ! 164: in the program itself. ! 165: ! 166: * If you send examples of assembler code output from GNU CC or GNU ! 167: C++, please use `-g' when you make them. The debugging information ! 168: includes source line numbers which are essential for correlating ! 169: the output with the input. ! 170: ! 171: * If you wish to mention something in the GNU CC source, refer to it ! 172: by context, not by line number. ! 173: ! 174: The line numbers in the development sources don't match those in ! 175: your sources. Your line numbers would convey no useful ! 176: information to the maintainers. ! 177: ! 178: * Additional information from a debugger might enable someone to ! 179: find a problem on a machine which he does not have available. ! 180: However, you need to think when you collect this information if ! 181: you want it to have any chance of being useful. ! 182: ! 183: For example, many people send just a backtrace, but that is never ! 184: useful by itself. A simple backtrace with arguments conveys little ! 185: about GNU CC because the compiler is largely data-driven; the same ! 186: functions are called over and over for different RTL insns, doing ! 187: different things depending on the details of the insn. ! 188: ! 189: Most of the arguments listed in the backtrace are useless because ! 190: they are pointers to RTL list structure. The numeric values of the ! 191: pointers, which the debugger prints in the backtrace, have no ! 192: significance whatever; all that matters is the contents of the ! 193: objects they point to (and most of the contents are other such ! 194: pointers). ! 195: ! 196: In addition, most compiler passes consist of one or more loops that ! 197: scan the RTL insn sequence. The most vital piece of information ! 198: about such a loop--which insn it has reached--is usually in a ! 199: local variable, not in an argument. ! 200: ! 201: What you need to provide in addition to a backtrace are the values ! 202: of the local variables for several stack frames up. When a local ! 203: variable or an argument is an RTX, first print its value and then ! 204: use the GDB command `pr' to print the RTL expression that it points ! 205: to. (If GDB doesn't run on your machine, use your debugger to call ! 206: the function `debug_rtx' with the RTX as an argument.) In ! 207: general, whenever a variable is a pointer, its value is no use ! 208: without the data it points to. ! 209: ! 210: Here are some things that are not necessary: ! 211: ! 212: * A description of the envelope of the bug. ! 213: ! 214: Often people who encounter a bug spend a lot of time investigating ! 215: which changes to the input file will make the bug go away and which ! 216: changes will not affect it. ! 217: ! 218: This is often time consuming and not very useful, because the way ! 219: we will find the bug is by running a single example under the ! 220: debugger with breakpoints, not by pure deduction from a series of ! 221: examples. You might as well save your time for something else. ! 222: ! 223: Of course, if you can find a simpler example to report *instead* of ! 224: the original one, that is a convenience. Errors in the output ! 225: will be easier to spot, running under the debugger will take less ! 226: time, etc. Most GNU CC bugs involve just one function, so the ! 227: most straightforward way to simplify an example is to delete all ! 228: the function definitions except the one where the bug occurs. ! 229: Those earlier in the file may be replaced by external declarations ! 230: if the crucial function depends on them. (Exception: inline ! 231: functions may affect compilation of functions defined later in the ! 232: file.) ! 233: ! 234: However, simplification is not vital; if you don't want to do this, ! 235: report the bug anyway and send the entire test case you used. ! 236: ! 237: * In particular, some people insert conditionals `#ifdef BUG' around ! 238: a statement which, if removed, makes the bug not happen. These ! 239: are just clutter; we won't pay any attention to them anyway. ! 240: Besides, you should send us cpp output, and that can't have ! 241: conditionals. ! 242: ! 243: * A patch for the bug. ! 244: ! 245: A patch for the bug is useful if it is a good one. But don't omit ! 246: the necessary information, such as the test case, on the ! 247: assumption that a patch is all we need. We might see problems ! 248: with your patch and decide to fix the problem another way, or we ! 249: might not understand it at all. ! 250: ! 251: Sometimes with a program as complicated as GNU CC it is very hard ! 252: to construct an example that will make the program follow a ! 253: certain path through the code. If you don't send the example, we ! 254: won't be able to construct one, so we won't be able to verify that ! 255: the bug is fixed. ! 256: ! 257: And if we can't understand what bug you are trying to fix, or why ! 258: your patch should be an improvement, we won't install it. A test ! 259: case will help us to understand. ! 260: ! 261: *Note Sending Patches::, for guidelines on how to make it easy for ! 262: us to understand and install your patches. ! 263: ! 264: * A guess about what the bug is or what it depends on. ! 265: ! 266: Such guesses are usually wrong. Even I can't guess right about ! 267: such things without first using the debugger to find the facts. ! 268: ! 269: * A core dump file. ! 270: ! 271: We have no way of examining a core dump for your type of machine ! 272: unless we have an identical system--and if we do have one, we ! 273: should be able to reproduce the crash ourselves. ! 274: ! 275: ! 276: File: gcc.info, Node: Sending Patches, Prev: Bug Reporting, Up: Bugs ! 277: ! 278: Sending Patches for GNU CC ! 279: ========================== ! 280: ! 281: If you would like to write bug fixes or improvements for the GNU C ! 282: compiler, that is very helpful. When you send your changes, please ! 283: follow these guidelines to avoid causing extra work for us in studying ! 284: the patches. ! 285: ! 286: If you don't follow these guidelines, your information might still be ! 287: useful, but using it will take extra work. Maintaining GNU C is a lot ! 288: of work in the best of circumstances, and we can't keep up unless you do ! 289: your best to help. ! 290: ! 291: * Send an explanation with your changes of what problem they fix or ! 292: what improvement they bring about. For a bug fix, just include a ! 293: copy of the bug report, and explain why the change fixes the bug. ! 294: ! 295: (Referring to a bug report is not as good as including it, because ! 296: then we will have to look it up, and we have probably already ! 297: deleted it if we've already fixed the bug.) ! 298: ! 299: * Always include a proper bug report for the problem you think you ! 300: have fixed. We need to convince ourselves that the change is ! 301: right before installing it. Even if it is right, we might have ! 302: trouble judging it if we don't have a way to reproduce the problem. ! 303: ! 304: * Include all the comments that are appropriate to help people ! 305: reading the source in the future understand why this change was ! 306: needed. ! 307: ! 308: * Don't mix together changes made for different reasons. Send them ! 309: *individually*. ! 310: ! 311: If you make two changes for separate reasons, then we might not ! 312: want to install them both. We might want to install just one. If ! 313: you send them all jumbled together in a single set of diffs, we ! 314: have to do extra work to disentangle them--to figure out which ! 315: parts of the change serve which purpose. If we don't have time ! 316: for this, we might have to ignore your changes entirely. ! 317: ! 318: If you send each change as soon as you have written it, with its ! 319: own explanation, then the two changes never get tangled up, and we ! 320: can consider each one properly without any extra work to ! 321: disentangle them. ! 322: ! 323: Ideally, each change you send should be impossible to subdivide ! 324: into parts that we might want to consider separately, because each ! 325: of its parts gets its motivation from the other parts. ! 326: ! 327: * Send each change as soon as that change is finished. Sometimes ! 328: people think they are helping us by accumulating many changes to ! 329: send them all together. As explained above, this is absolutely ! 330: the worst thing you could do. ! 331: ! 332: Since you should send each change separately, you might as well ! 333: send it right away. That gives us the option of installing it ! 334: immediately if it is important. ! 335: ! 336: * Use `diff -c' to make your diffs. Diffs without context are hard ! 337: for us to install reliably. More than that, they make it hard for ! 338: us to study the diffs to decide whether we want to install them. ! 339: Unidiff format is better than contextless diffs, but not as easy ! 340: to read as `-c' format. ! 341: ! 342: If you have GNU diff, use `diff -cp', which shows the name of the ! 343: function that each change occurs in. ! 344: ! 345: * Write the change log entries for your changes. We get lots of ! 346: changes, and we don't have time to do all the change log writing ! 347: ourselves. ! 348: ! 349: Read the `ChangeLog' file to see what sorts of information to put ! 350: in, and to learn the style that we use. The purpose of the change ! 351: log is to show people where to find what was changed. So you need ! 352: to be specific about what functions you changed; in large ! 353: functions, it's often helpful to indicate where within the ! 354: function the change was. ! 355: ! 356: On the other hand, once you have shown people where to find the ! 357: change, you need not explain its purpose. Thus, if you add a new ! 358: function, all you need to say about it is that it is new. If you ! 359: feel that the purpose needs explaining, it probably does--but the ! 360: explanation will be much more useful if you put it in comments in ! 361: the code. ! 362: ! 363: If you would like your name to appear in the header line for who ! 364: made the change, send us the header line. ! 365: ! 366: * When you write the fix, keep in mind that we can't install a ! 367: change that would break other systems. ! 368: ! 369: People often suggest fixing a problem by changing ! 370: machine-independent files such as `toplev.c' to do something ! 371: special that a particular system needs. Sometimes it is totally ! 372: obvious that such changes would break GNU CC for almost all users. ! 373: We can't possibly make a change like that. At best it might tell ! 374: us how to write another patch that would solve the problem ! 375: acceptably. ! 376: ! 377: Sometimes people send fixes that *might* be an improvement in ! 378: general--but it is hard to be sure of this. It's hard to install ! 379: such changes because we have to study them very carefully. Of ! 380: course, a good explanation of the reasoning by which you concluded ! 381: the change was correct can help convince us. ! 382: ! 383: The safest changes are changes to the configuration files for a ! 384: particular machine. These are safe because they can't create new ! 385: bugs on other machines. ! 386: ! 387: Please help us keep up with the workload by designing the patch in ! 388: a form that is good to install. ! 389: ! 390: ! 391: File: gcc.info, Node: Service, Next: VMS, Prev: Bugs, Up: Top ! 392: ! 393: How To Get Help with GNU CC ! 394: *************************** ! 395: ! 396: If you need help installing, using or changing GNU CC, there are two ! 397: ways to find it: ! 398: ! 399: * Send a message to a suitable network mailing list. First try ! 400: `[email protected]', and if that brings no response, try ! 401: `[email protected]'. ! 402: ! 403: * Look in the service directory for someone who might help you for a ! 404: fee. The service directory is found in the file named `SERVICE' ! 405: in the GNU CC distribution. ! 406: ! 407: ! 408: File: gcc.info, Node: VMS, Next: Portability, Prev: Service, Up: Top ! 409: ! 410: Using GNU CC on VMS ! 411: ******************* ! 412: ! 413: * Menu: ! 414: ! 415: * Include Files and VMS:: Where the preprocessor looks for the include files. ! 416: * Global Declarations:: How to do globaldef, globalref and globalvalue with ! 417: GNU CC. ! 418: * VMS Misc:: Misc information. ! 419: ! 420: ! 421: File: gcc.info, Node: Include Files and VMS, Next: Global Declarations, Up: VMS ! 422: ! 423: Include Files and VMS ! 424: ===================== ! 425: ! 426: Due to the differences between the filesystems of Unix and VMS, GNU ! 427: CC attempts to translate file names in `#include' into names that VMS ! 428: will understand. The basic strategy is to prepend a prefix to the ! 429: specification of the include file, convert the whole filename to a VMS ! 430: filename, and then try to open the file. GNU CC tries various prefixes ! 431: one by one until one of them succeeds: ! 432: ! 433: 1. The first prefix is the `GNU_CC_INCLUDE:' logical name: this is ! 434: where GNU C header files are traditionally stored. If you wish to ! 435: store header files in non-standard locations, then you can assign ! 436: the logical `GNU_CC_INCLUDE' to be a search list, where each ! 437: element of the list is suitable for use with a rooted logical. ! 438: ! 439: 2. The next prefix tried is `SYS$SYSROOT:[SYSLIB.]'. This is where ! 440: VAX-C header files are traditionally stored. ! 441: ! 442: 3. If the include file specification by itself is a valid VMS ! 443: filename, the preprocessor then uses this name with no prefix in ! 444: an attempt to open the include file. ! 445: ! 446: 4. If the file specification is not a valid VMS filename (i.e. does ! 447: not contain a device or a directory specifier, and contains a `/' ! 448: character), the preprocessor tries to convert it from Unix syntax ! 449: to VMS syntax. ! 450: ! 451: Conversion works like this: the first directory name becomes a ! 452: device, and the rest of the directories are converted into ! 453: VMS-format directory names. For example, the name `X11/foobar.h' ! 454: is translated to `X11:[000000]foobar.h' or `X11:foobar.h', ! 455: whichever one can be opened. This strategy allows you to assign a ! 456: logical name to point to the actual location of the header files. ! 457: ! 458: 5. If none of these strategies succeeds, the `#include' fails. ! 459: ! 460: Include directives of the form: ! 461: ! 462: #include foobar ! 463: ! 464: are a common source of incompatibility between VAX-C and GNU CC. VAX-C ! 465: treats this much like a standard `#include <foobar.h>' directive. That ! 466: is incompatible with the ANSI C behavior implemented by GNU CC: to ! 467: expand the name `foobar' as a macro. Macro expansion should eventually ! 468: yield one of the two standard formats for `#include': ! 469: ! 470: #include "FILE" ! 471: #include <FILE> ! 472: ! 473: If you have this problem, the best solution is to modify the source ! 474: to convert the `#include' directives to one of the two standard forms. ! 475: That will work with either compiler. If you want a quick and dirty fix, ! 476: define the file names as macros with the proper expansion, like this: ! 477: ! 478: #define stdio <stdio.h> ! 479: ! 480: This will work, as long as the name doesn't conflict with anything else ! 481: in the program. ! 482: ! 483: Another source of incompatibility is that VAX-C assumes that: ! 484: ! 485: #include "foobar" ! 486: ! 487: is actually asking for the file `foobar.h'. GNU CC does not make this ! 488: assumption, and instead takes what you ask for literally; it tries to ! 489: read the file `foobar'. The best way to avoid this problem is to ! 490: always specify the desired file extension in your include directives. ! 491: ! 492: GNU CC for VMS is distributed with a set of include files that is ! 493: sufficient to compile most general purpose programs. Even though the ! 494: GNU CC distribution does not contain header files to define constants ! 495: and structures for some VMS system-specific functions, there is no ! 496: reason why you cannot use GNU CC with any of these functions. You first ! 497: may have to generate or create header files, either by using the public ! 498: domain utility `UNSDL' (which can be found on a DECUS tape), or by ! 499: extracting the relevant modules from one of the system macro libraries, ! 500: and using an editor to construct a C header file. ! 501: ! 502: A `#include' file name cannot contain a DECNET node name. The ! 503: preprocessor reports an I/O error if you attempt to use a node name, ! 504: whether explicitly, or implicitly via a logical name. ! 505: ! 506: ! 507: File: gcc.info, Node: Global Declarations, Next: VMS Misc, Prev: Include Files and VMS, Up: VMS ! 508: ! 509: Global Declarations and VMS ! 510: =========================== ! 511: ! 512: GNU CC does not provide the `globalref', `globaldef' and ! 513: `globalvalue' keywords of VAX-C. You can get the same effect with an ! 514: obscure feature of GAS, the GNU assembler. (This requires GAS version ! 515: 1.39 or later.) The following macros allow you to use this feature in ! 516: a fairly natural way: ! 517: ! 518: #ifdef __GNUC__ ! 519: #define GLOBALREF(TYPE,NAME) \ ! 520: TYPE NAME \ ! 521: asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME) ! 522: #define GLOBALDEF(TYPE,NAME,VALUE) \ ! 523: TYPE NAME \ ! 524: asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME) \ ! 525: = VALUE ! 526: #define GLOBALVALUEREF(TYPE,NAME) \ ! 527: const TYPE NAME[1] \ ! 528: asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME) ! 529: #define GLOBALVALUEDEF(TYPE,NAME,VALUE) \ ! 530: const TYPE NAME[1] \ ! 531: asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME) \ ! 532: = {VALUE} ! 533: #else ! 534: #define GLOBALREF(TYPE,NAME) \ ! 535: globalref TYPE NAME ! 536: #define GLOBALDEF(TYPE,NAME,VALUE) \ ! 537: globaldef TYPE NAME = VALUE ! 538: #define GLOBALVALUEDEF(TYPE,NAME,VALUE) \ ! 539: globalvalue TYPE NAME = VALUE ! 540: #define GLOBALVALUEREF(TYPE,NAME) \ ! 541: globalvalue TYPE NAME ! 542: #endif ! 543: ! 544: (The `_$$PsectAttributes_GLOBALSYMBOL' prefix at the start of the name ! 545: is removed by the assembler, after it has modified the attributes of ! 546: the symbol). These macros are provided in the VMS binaries ! 547: distribution in a header file `GNU_HACKS.H'. An example of the usage ! 548: is: ! 549: ! 550: GLOBALREF (int, ijk); ! 551: GLOBALDEF (int, jkl, 0); ! 552: ! 553: The macros `GLOBALREF' and `GLOBALDEF' cannot be used ! 554: straightforwardly for arrays, since there is no way to insert the array ! 555: dimension into the declaration at the right place. However, you can ! 556: declare an array with these macros if you first define a typedef for the ! 557: array type, like this: ! 558: ! 559: typedef int intvector[10]; ! 560: GLOBALREF (intvector, foo); ! 561: ! 562: Array and structure initializers will also break the macros; you can ! 563: define the initializer to be a macro of its own, or you can expand the ! 564: `GLOBALDEF' macro by hand. You may find a case where you wish to use ! 565: the `GLOBALDEF' macro with a large array, but you are not interested in ! 566: explicitly initializing each element of the array. In such cases you ! 567: can use an initializer like: `{0,}', which will initialize the entire ! 568: array to `0'. ! 569: ! 570: A shortcoming of this implementation is that a variable declared with ! 571: `GLOBALVALUEREF' or `GLOBALVALUEDEF' is always an array. For example, ! 572: the declaration: ! 573: ! 574: GLOBALVALUEREF(int, ijk); ! 575: ! 576: declares the variable `ijk' as an array of type `int [1]'. This is ! 577: done because a globalvalue is actually a constant; its "value" is what ! 578: the linker would normally consider an address. That is not how an ! 579: integer value works in C, but it is how an array works. So treating ! 580: the symbol as an array name gives consistent results--with the ! 581: exception that the value seems to have the wrong type. *Don't try to ! 582: access an element of the array.* It doesn't have any elements. The ! 583: array "address" may not be the address of actual storage. ! 584: ! 585: The fact that the symbol is an array may lead to warnings where the ! 586: variable is used. Insert type casts to avoid the warnings. Here is an ! 587: example; it takes advantage of the ANSI C feature allowing macros that ! 588: expand to use the same name as the macro itself. ! 589: ! 590: GLOBALVALUEREF (int, ss$_normal); ! 591: GLOBALVALUEDEF (int, xyzzy,123); ! 592: #ifdef __GNUC__ ! 593: #define ss$_normal ((int) ss$_normal) ! 594: #define xyzzy ((int) xyzzy) ! 595: #endif ! 596: ! 597: Don't use `globaldef' or `globalref' with a variable whose type is ! 598: an enumeration type; this is not implemented. Instead, make the ! 599: variable an integer, and use a `globalvaluedef' for each of the ! 600: enumeration values. An example of this would be: ! 601: ! 602: #ifdef __GNUC__ ! 603: GLOBALDEF (int, color, 0); ! 604: GLOBALVALUEDEF (int, RED, 0); ! 605: GLOBALVALUEDEF (int, BLUE, 1); ! 606: GLOBALVALUEDEF (int, GREEN, 3); ! 607: #else ! 608: enum globaldef color {RED, BLUE, GREEN = 3}; ! 609: #endif ! 610: ! 611: ! 612: File: gcc.info, Node: VMS Misc, Prev: Global Declarations, Up: VMS ! 613: ! 614: Other VMS Issues ! 615: ================ ! 616: ! 617: GNU CC automatically arranges for `main' to return 1 by default if ! 618: you fail to specify an explicit return value. This will be interpreted ! 619: by VMS as a status code indicating a normal successful completion. ! 620: Version 1 of GNU CC did not provide this default. ! 621: ! 622: GNU CC on VMS works only with the GNU assembler, GAS. You need ! 623: version 1.37 or later of GAS in order to produce value debugging ! 624: information for the VMS debugger. Use the ordinary VMS linker with the ! 625: object files produced by GAS. ! 626: ! 627: Under previous versions of GNU CC, the generated code would ! 628: occasionally give strange results when linked to the sharable `VAXCRTL' ! 629: library. Now this should work. ! 630: ! 631: A caveat for use of `const' global variables: the `const' modifier ! 632: must be specified in every external declaration of the variable in all ! 633: of the source files that use that variable. Otherwise the linker will ! 634: issue warnings about conflicting attributes for the variable. Your ! 635: program will still work despite the warnings, but the variable will be ! 636: placed in writable storage. ! 637: ! 638: Although the VMS linker does distinguish between upper and lower case ! 639: letters in global symbols, most VMS compilers convert all such symbols ! 640: into upper case and most run-time library routines also have upper case ! 641: names. To be able to reliably call such routines, GNU CC (by means of ! 642: the assembler GAS) converts global symbols into upper case like other ! 643: VMS compilers. However, since the usual practice in C is to distinguish ! 644: case, GNU CC (via GAS) tries to preserve usual C behavior by augmenting ! 645: each name that is not all lower case. This means truncating the name ! 646: to at most 23 characters and then adding more characters at the end ! 647: which encode the case pattern of those 23. Names which contain at ! 648: least one dollar sign are an exception; they are converted directly into ! 649: upper case without augmentation. ! 650: ! 651: Name augmentation yields bad results for programs that use ! 652: precompiled libraries (such as Xlib) which were generated by another ! 653: compiler. You can use the compiler option `/NOCASE_HACK' to inhibit ! 654: augmentation; it makes external C functions and variables ! 655: case-independent as is usual on VMS. Alternatively, you could write ! 656: all references to the functions and variables in such libraries using ! 657: lower case; this will work on VMS, but is not portable to other ! 658: systems. The compiler option `/NAMES' also provides control over ! 659: global name handling. ! 660: ! 661: Function and variable names are handled somewhat differently with GNU ! 662: C++. The GNU C++ compiler performs "name mangling" on function names, ! 663: which means that it adds information to the function name to describe ! 664: the data types of the arguments that the function takes. One result of ! 665: this is that the name of a function can become very long. Since the ! 666: VMS linker only recognizes the first 31 characters in a name, special ! 667: action is taken to ensure that each function and variable has a unique ! 668: name that can be represented in 31 characters. ! 669: ! 670: If the name (plus a name augmentation, if required) is less than 32 ! 671: characters in length, then no special action is performed. If the name ! 672: is longer than 31 characters, the assembler (GAS) will generate a hash ! 673: string based upon the function name, truncate the function name to 23 ! 674: characters, and append the hash string to the truncated name. If the ! 675: `/VERBOSE' compiler option is used, the assembler will print both the ! 676: full and truncated names of each symbol that is truncated. ! 677: ! 678: The `/NOCASE_HACK' compiler option should not be used when you are ! 679: compiling programs that use libg++. libg++ has several instances of ! 680: objects (i.e. `Filebuf' and `filebuf') which become indistinguishable ! 681: in a case-insensitive environment. This leads to cases where you need ! 682: to inhibit augmentation selectively (if you were using libg++ and Xlib ! 683: in the same program, for example). There is no special feature for ! 684: doing this, but you can get the result by defining a macro for each ! 685: mixed case symbol for which you wish to inhibit augmentation. The ! 686: macro should expand into the lower case equivalent of itself. For ! 687: example: ! 688: ! 689: #define StuDlyCapS studlycaps ! 690: ! 691: These macro definitions can be placed in a header file to minimize ! 692: the number of changes to your source code. ! 693: ! 694: ! 695: File: gcc.info, Node: Portability, Next: Interface, Prev: VMS, Up: Top ! 696: ! 697: GNU CC and Portability ! 698: ********************** ! 699: ! 700: The main goal of GNU CC was to make a good, fast compiler for ! 701: machines in the class that the GNU system aims to run on: 32-bit ! 702: machines that address 8-bit bytes and have several general registers. ! 703: Elegance, theoretical power and simplicity are only secondary. ! 704: ! 705: GNU CC gets most of the information about the target machine from a ! 706: machine description which gives an algebraic formula for each of the ! 707: machine's instructions. This is a very clean way to describe the ! 708: target. But when the compiler needs information that is difficult to ! 709: express in this fashion, I have not hesitated to define an ad-hoc ! 710: parameter to the machine description. The purpose of portability is to ! 711: reduce the total work needed on the compiler; it was not of interest ! 712: for its own sake. ! 713: ! 714: GNU CC does not contain machine dependent code, but it does contain ! 715: code that depends on machine parameters such as endianness (whether the ! 716: most significant byte has the highest or lowest address of the bytes in ! 717: a word) and the availability of autoincrement addressing. In the ! 718: RTL-generation pass, it is often necessary to have multiple strategies ! 719: for generating code for a particular kind of syntax tree, strategies ! 720: that are usable for different combinations of parameters. Often I have ! 721: not tried to address all possible cases, but only the common ones or ! 722: only the ones that I have encountered. As a result, a new target may ! 723: require additional strategies. You will know if this happens because ! 724: the compiler will call `abort'. Fortunately, the new strategies can be ! 725: added in a machine-independent fashion, and will affect only the target ! 726: machines that need them. ! 727: ! 728: ! 729: File: gcc.info, Node: Interface, Next: Passes, Prev: Portability, Up: Top ! 730: ! 731: Interfacing to GNU CC Output ! 732: **************************** ! 733: ! 734: GNU CC is normally configured to use the same function calling ! 735: convention normally in use on the target system. This is done with the ! 736: machine-description macros described (*note Target Macros::.). ! 737: ! 738: However, returning of structure and union values is done differently ! 739: on some target machines. As a result, functions compiled with PCC ! 740: returning such types cannot be called from code compiled with GNU CC, ! 741: and vice versa. This does not cause trouble often because few Unix ! 742: library routines return structures or unions. ! 743: ! 744: GNU CC code returns structures and unions that are 1, 2, 4 or 8 bytes ! 745: long in the same registers used for `int' or `double' return values. ! 746: (GNU CC typically allocates variables of such types in registers also.) ! 747: Structures and unions of other sizes are returned by storing them into ! 748: an address passed by the caller (usually in a register). The ! 749: machine-description macros `STRUCT_VALUE' and `STRUCT_INCOMING_VALUE' ! 750: tell GNU CC where to pass this address. ! 751: ! 752: By contrast, PCC on most target machines returns structures and ! 753: unions of any size by copying the data into an area of static storage, ! 754: and then returning the address of that storage as if it were a pointer ! 755: value. The caller must copy the data from that memory area to the ! 756: place where the value is wanted. This is slower than the method used ! 757: by GNU CC, and fails to be reentrant. ! 758: ! 759: On some target machines, such as RISC machines and the 80386, the ! 760: standard system convention is to pass to the subroutine the address of ! 761: where to return the value. On these machines, GNU CC has been ! 762: configured to be compatible with the standard compiler, when this method ! 763: is used. It may not be compatible for structures of 1, 2, 4 or 8 bytes. ! 764: ! 765: GNU CC uses the system's standard convention for passing arguments. ! 766: On some machines, the first few arguments are passed in registers; in ! 767: others, all are passed on the stack. It would be possible to use ! 768: registers for argument passing on any machine, and this would probably ! 769: result in a significant speedup. But the result would be complete ! 770: incompatibility with code that follows the standard convention. So this ! 771: change is practical only if you are switching to GNU CC as the sole C ! 772: compiler for the system. We may implement register argument passing on ! 773: certain machines once we have a complete GNU system so that we can ! 774: compile the libraries with GNU CC. ! 775: ! 776: On some machines (particularly the Sparc), certain types of arguments ! 777: are passed "by invisible reference". This means that the value is ! 778: stored in memory, and the address of the memory location is passed to ! 779: the subroutine. ! 780: ! 781: If you use `longjmp', beware of automatic variables. ANSI C says ! 782: that automatic variables that are not declared `volatile' have undefined ! 783: values after a `longjmp'. And this is all GNU CC promises to do, ! 784: because it is very difficult to restore register variables correctly, ! 785: and one of GNU CC's features is that it can put variables in registers ! 786: without your asking it to. ! 787: ! 788: If you want a variable to be unaltered by `longjmp', and you don't ! 789: want to write `volatile' because old C compilers don't accept it, just ! 790: take the address of the variable. If a variable's address is ever ! 791: taken, even if just to compute it and ignore it, then the variable ! 792: cannot go in a register: ! 793: ! 794: { ! 795: int careful; ! 796: &careful; ! 797: ... ! 798: } ! 799: ! 800: Code compiled with GNU CC may call certain library routines. Most of ! 801: them handle arithmetic for which there are no instructions. This ! 802: includes multiply and divide on some machines, and floating point ! 803: operations on any machine for which floating point support is disabled ! 804: with `-msoft-float'. Some standard parts of the C library, such as ! 805: `bcopy' or `memcpy', are also called automatically. The usual function ! 806: call interface is used for calling the library routines. ! 807: ! 808: These library routines should be defined in the library `libgcc.a', ! 809: which GNU CC automatically searches whenever it links a program. On ! 810: machines that have multiply and divide instructions, if hardware ! 811: floating point is in use, normally `libgcc.a' is not needed, but it is ! 812: searched just in case. ! 813: ! 814: Each arithmetic function is defined in `libgcc1.c' to use the ! 815: corresponding C arithmetic operator. As long as the file is compiled ! 816: with another C compiler, which supports all the C arithmetic operators, ! 817: this file will work portably. However, `libgcc1.c' does not work if ! 818: compiled with GNU CC, because each arithmetic function would compile ! 819: into a call to itself! ! 820:
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