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diff --git a/gcc/gcc.info-13 b/gcc/gcc.info-13 deleted file mode 100644 index baeaa8a80fe..00000000000 --- a/gcc/gcc.info-13 +++ /dev/null @@ -1,853 +0,0 @@ -This is Info file gcc.info, produced by Makeinfo version 1.68 from the -input file gcc.texi. - - This file documents the use and the internals of the GNU compiler. - - Published by the Free Software Foundation 59 Temple Place - Suite 330 -Boston, MA 02111-1307 USA - - Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997 Free -Software Foundation, Inc. - - Permission is granted to make and distribute verbatim copies of this -manual provided the copyright notice and this permission notice are -preserved on all copies. - - Permission is granted to copy and distribute modified versions of -this manual under the conditions for verbatim copying, provided also -that the sections entitled "GNU General Public License," "Funding for -Free Software," and "Protect Your Freedom--Fight `Look And Feel'" are -included exactly as in the original, and provided that the entire -resulting derived work is distributed under the terms of a permission -notice identical to this one. - - Permission is granted to copy and distribute translations of this -manual into another language, under the above conditions for modified -versions, except that the sections entitled "GNU General Public -License," "Funding for Free Software," and "Protect Your Freedom--Fight -`Look And Feel'", and this permission notice, may be included in -translations approved by the Free Software Foundation instead of in the -original English. - - -File: gcc.info, Node: Bug Reporting, Next: Sending Patches, Prev: Bug Lists, Up: Bugs - -How to Report Bugs -================== - - The fundamental principle of reporting bugs usefully is this: -*report all the facts*. If you are not sure whether to state a fact or -leave it out, state it! - - Often people omit facts because they think they know what causes the -problem and they conclude that some details don't matter. Thus, you -might assume that the name of the variable you use in an example does -not matter. Well, probably it doesn't, but one cannot be sure. -Perhaps the bug is a stray memory reference which happens to fetch from -the location where that name is stored in memory; perhaps, if the name -were different, the contents of that location would fool the compiler -into doing the right thing despite the bug. Play it safe and give a -specific, complete example. That is the easiest thing for you to do, -and the most helpful. - - Keep in mind that the purpose of a bug report is to enable someone to -fix the bug if it is not known. It isn't very important what happens if -the bug is already known. Therefore, always write your bug reports on -the assumption that the bug is not known. - - Sometimes people give a few sketchy facts and ask, "Does this ring a -bell?" This cannot help us fix a bug, so it is basically useless. We -respond by asking for enough details to enable us to investigate. You -might as well expedite matters by sending them to begin with. - - Try to make your bug report self-contained. If we have to ask you -for more information, it is best if you include all the previous -information in your response, as well as the information that was -missing. - - Please report each bug in a separate message. This makes it easier -for us to track which bugs have been fixed and to forward your bugs -reports to the appropriate maintainer. - - Do not compress and encode any part of your bug report using programs -such as `uuencode'. If you do so it will slow down the processing of -your bug. If you must submit multiple large files, use `shar', which -allows us to read your message without having to run any decompression -programs. - - To enable someone to investigate the bug, you should include all -these things: - - * The version of GNU CC. You can get this by running it with the - `-v' option. - - Without this, we won't know whether there is any point in looking - for the bug in the current version of GNU CC. - - * A complete input file that will reproduce the bug. If the bug is - in the C preprocessor, send a source file and any header files - that it requires. If the bug is in the compiler proper (`cc1'), - run your source file through the C preprocessor by doing `gcc -E - SOURCEFILE > OUTFILE', then include the contents of OUTFILE in the - bug report. (When you do this, use the same `-I', `-D' or `-U' - options that you used in actual compilation.) - - A single statement is not enough of an example. In order to - compile it, it must be embedded in a complete file of compiler - input; and the bug might depend on the details of how this is done. - - Without a real example one can compile, all anyone can do about - your bug report is wish you luck. It would be futile to try to - guess how to provoke the bug. For example, bugs in register - allocation and reloading frequently depend on every little detail - of the function they happen in. - - Even if the input file that fails comes from a GNU program, you - should still send the complete test case. Don't ask the GNU CC - maintainers to do the extra work of obtaining the program in - question--they are all overworked as it is. Also, the problem may - depend on what is in the header files on your system; it is - unreliable for the GNU CC maintainers to try the problem with the - header files available to them. By sending CPP output, you can - eliminate this source of uncertainty and save us a certain - percentage of wild goose chases. - - * The command arguments you gave GNU CC or GNU C++ to compile that - example and observe the bug. For example, did you use `-O'? To - guarantee you won't omit something important, list all the options. - - If we were to try to guess the arguments, we would probably guess - wrong and then we would not encounter the bug. - - * The type of machine you are using, and the operating system name - and version number. - - * The operands you gave to the `configure' command when you installed - the compiler. - - * A complete list of any modifications you have made to the compiler - source. (We don't promise to investigate the bug unless it - happens in an unmodified compiler. But if you've made - modifications and don't tell us, then you are sending us on a wild - goose chase.) - - Be precise about these changes. A description in English is not - enough--send a context diff for them. - - Adding files of your own (such as a machine description for a - machine we don't support) is a modification of the compiler source. - - * Details of any other deviations from the standard procedure for - installing GNU CC. - - * A description of what behavior you observe that you believe is - incorrect. For example, "The compiler gets a fatal signal," or, - "The assembler instruction at line 208 in the output is incorrect." - - Of course, if the bug is that the compiler gets a fatal signal, - then one can't miss it. But if the bug is incorrect output, the - maintainer might not notice unless it is glaringly wrong. None of - us has time to study all the assembler code from a 50-line C - program just on the chance that one instruction might be wrong. - We need *you* to do this part! - - Even if the problem you experience is a fatal signal, you should - still say so explicitly. Suppose something strange is going on, - such as, your copy of the compiler is out of synch, or you have - encountered a bug in the C library on your system. (This has - happened!) Your copy might crash and the copy here would not. If - you said to expect a crash, then when the compiler here fails to - crash, we would know that the bug was not happening. If you don't - say to expect a crash, then we would not know whether the bug was - happening. We would not be able to draw any conclusion from our - observations. - - If the problem is a diagnostic when compiling GNU CC with some - other compiler, say whether it is a warning or an error. - - Often the observed symptom is incorrect output when your program - is run. Sad to say, this is not enough information unless the - program is short and simple. None of us has time to study a large - program to figure out how it would work if compiled correctly, - much less which line of it was compiled wrong. So you will have - to do that. Tell us which source line it is, and what incorrect - result happens when that line is executed. A person who - understands the program can find this as easily as finding a bug - in the program itself. - - * If you send examples of assembler code output from GNU CC or GNU - C++, please use `-g' when you make them. The debugging information - includes source line numbers which are essential for correlating - the output with the input. - - * If you wish to mention something in the GNU CC source, refer to it - by context, not by line number. - - The line numbers in the development sources don't match those in - your sources. Your line numbers would convey no useful - information to the maintainers. - - * Additional information from a debugger might enable someone to - find a problem on a machine which he does not have available. - However, you need to think when you collect this information if - you want it to have any chance of being useful. - - For example, many people send just a backtrace, but that is never - useful by itself. A simple backtrace with arguments conveys little - about GNU CC because the compiler is largely data-driven; the same - functions are called over and over for different RTL insns, doing - different things depending on the details of the insn. - - Most of the arguments listed in the backtrace are useless because - they are pointers to RTL list structure. The numeric values of the - pointers, which the debugger prints in the backtrace, have no - significance whatever; all that matters is the contents of the - objects they point to (and most of the contents are other such - pointers). - - In addition, most compiler passes consist of one or more loops that - scan the RTL insn sequence. The most vital piece of information - about such a loop--which insn it has reached--is usually in a - local variable, not in an argument. - - What you need to provide in addition to a backtrace are the values - of the local variables for several stack frames up. When a local - variable or an argument is an RTX, first print its value and then - use the GDB command `pr' to print the RTL expression that it points - to. (If GDB doesn't run on your machine, use your debugger to call - the function `debug_rtx' with the RTX as an argument.) In - general, whenever a variable is a pointer, its value is no use - without the data it points to. - - Here are some things that are not necessary: - - * A description of the envelope of the bug. - - Often people who encounter a bug spend a lot of time investigating - which changes to the input file will make the bug go away and which - changes will not affect it. - - This is often time consuming and not very useful, because the way - we will find the bug is by running a single example under the - debugger with breakpoints, not by pure deduction from a series of - examples. You might as well save your time for something else. - - Of course, if you can find a simpler example to report *instead* of - the original one, that is a convenience. Errors in the output - will be easier to spot, running under the debugger will take less - time, etc. Most GNU CC bugs involve just one function, so the - most straightforward way to simplify an example is to delete all - the function definitions except the one where the bug occurs. - Those earlier in the file may be replaced by external declarations - if the crucial function depends on them. (Exception: inline - functions may affect compilation of functions defined later in the - file.) - - However, simplification is not vital; if you don't want to do this, - report the bug anyway and send the entire test case you used. - - * In particular, some people insert conditionals `#ifdef BUG' around - a statement which, if removed, makes the bug not happen. These - are just clutter; we won't pay any attention to them anyway. - Besides, you should send us cpp output, and that can't have - conditionals. - - * A patch for the bug. - - A patch for the bug is useful if it is a good one. But don't omit - the necessary information, such as the test case, on the - assumption that a patch is all we need. We might see problems - with your patch and decide to fix the problem another way, or we - might not understand it at all. - - Sometimes with a program as complicated as GNU CC it is very hard - to construct an example that will make the program follow a - certain path through the code. If you don't send the example, we - won't be able to construct one, so we won't be able to verify that - the bug is fixed. - - And if we can't understand what bug you are trying to fix, or why - your patch should be an improvement, we won't install it. A test - case will help us to understand. - - *Note Sending Patches::, for guidelines on how to make it easy for - us to understand and install your patches. - - * A guess about what the bug is or what it depends on. - - Such guesses are usually wrong. Even I can't guess right about - such things without first using the debugger to find the facts. - - * A core dump file. - - We have no way of examining a core dump for your type of machine - unless we have an identical system--and if we do have one, we - should be able to reproduce the crash ourselves. - - -File: gcc.info, Node: Sending Patches, Prev: Bug Reporting, Up: Bugs - -Sending Patches for GNU CC -========================== - - If you would like to write bug fixes or improvements for the GNU C -compiler, that is very helpful. Send suggested fixes to the bug report -mailing list, `bug-gcc@prep.ai.mit.edu'. - - Please follow these guidelines so we can study your patches -efficiently. If you don't follow these guidelines, your information -might still be useful, but using it will take extra work. Maintaining -GNU C is a lot of work in the best of circumstances, and we can't keep -up unless you do your best to help. - - * Send an explanation with your changes of what problem they fix or - what improvement they bring about. For a bug fix, just include a - copy of the bug report, and explain why the change fixes the bug. - - (Referring to a bug report is not as good as including it, because - then we will have to look it up, and we have probably already - deleted it if we've already fixed the bug.) - - * Always include a proper bug report for the problem you think you - have fixed. We need to convince ourselves that the change is - right before installing it. Even if it is right, we might have - trouble judging it if we don't have a way to reproduce the problem. - - * Include all the comments that are appropriate to help people - reading the source in the future understand why this change was - needed. - - * Don't mix together changes made for different reasons. Send them - *individually*. - - If you make two changes for separate reasons, then we might not - want to install them both. We might want to install just one. If - you send them all jumbled together in a single set of diffs, we - have to do extra work to disentangle them--to figure out which - parts of the change serve which purpose. If we don't have time - for this, we might have to ignore your changes entirely. - - If you send each change as soon as you have written it, with its - own explanation, then the two changes never get tangled up, and we - can consider each one properly without any extra work to - disentangle them. - - Ideally, each change you send should be impossible to subdivide - into parts that we might want to consider separately, because each - of its parts gets its motivation from the other parts. - - * Send each change as soon as that change is finished. Sometimes - people think they are helping us by accumulating many changes to - send them all together. As explained above, this is absolutely - the worst thing you could do. - - Since you should send each change separately, you might as well - send it right away. That gives us the option of installing it - immediately if it is important. - - * Use `diff -c' to make your diffs. Diffs without context are hard - for us to install reliably. More than that, they make it hard for - us to study the diffs to decide whether we want to install them. - Unidiff format is better than contextless diffs, but not as easy - to read as `-c' format. - - If you have GNU diff, use `diff -cp', which shows the name of the - function that each change occurs in. - - * Write the change log entries for your changes. We get lots of - changes, and we don't have time to do all the change log writing - ourselves. - - Read the `ChangeLog' file to see what sorts of information to put - in, and to learn the style that we use. The purpose of the change - log is to show people where to find what was changed. So you need - to be specific about what functions you changed; in large - functions, it's often helpful to indicate where within the - function the change was. - - On the other hand, once you have shown people where to find the - change, you need not explain its purpose. Thus, if you add a new - function, all you need to say about it is that it is new. If you - feel that the purpose needs explaining, it probably does--but the - explanation will be much more useful if you put it in comments in - the code. - - If you would like your name to appear in the header line for who - made the change, send us the header line. - - * When you write the fix, keep in mind that we can't install a - change that would break other systems. - - People often suggest fixing a problem by changing - machine-independent files such as `toplev.c' to do something - special that a particular system needs. Sometimes it is totally - obvious that such changes would break GNU CC for almost all users. - We can't possibly make a change like that. At best it might tell - us how to write another patch that would solve the problem - acceptably. - - Sometimes people send fixes that *might* be an improvement in - general--but it is hard to be sure of this. It's hard to install - such changes because we have to study them very carefully. Of - course, a good explanation of the reasoning by which you concluded - the change was correct can help convince us. - - The safest changes are changes to the configuration files for a - particular machine. These are safe because they can't create new - bugs on other machines. - - Please help us keep up with the workload by designing the patch in - a form that is good to install. - - -File: gcc.info, Node: Service, Next: Contributing, Prev: Bugs, Up: Top - -How To Get Help with GNU CC -*************************** - - If you need help installing, using or changing GNU CC, there are two -ways to find it: - - * Send a message to a suitable network mailing list. First try - `bug-gcc@prep.ai.mit.edu', and if that brings no response, try - `help-gcc@prep.ai.mit.edu'. - - * Look in the service directory for someone who might help you for a - fee. The service directory is found in the file named `SERVICE' - in the GNU CC distribution. - - -File: gcc.info, Node: Contributing, Next: VMS, Prev: Service, Up: Top - -Contributing to GNU CC Development -********************************** - - If you would like to help pretest GNU CC releases to assure they work -well, or if you would like to work on improving GNU CC, please contact -the maintainers at `bug-gcc@gnu.ai.mit.edu'. A pretester should be -willing to try to investigate bugs as well as report them. - - If you'd like to work on improvements, please ask for suggested -projects or suggest your own ideas. If you have already written an -improvement, please tell us about it. If you have not yet started -work, it is useful to contact `bug-gcc@prep.ai.mit.edu' before you -start; the maintainers may be able to suggest ways to make your -extension fit in better with the rest of GNU CC and with other -development plans. - - -File: gcc.info, Node: VMS, Next: Portability, Prev: Contributing, Up: Top - -Using GNU CC on VMS -******************* - - Here is how to use GNU CC on VMS. - -* Menu: - -* Include Files and VMS:: Where the preprocessor looks for the include files. -* Global Declarations:: How to do globaldef, globalref and globalvalue with - GNU CC. -* VMS Misc:: Misc information. - - -File: gcc.info, Node: Include Files and VMS, Next: Global Declarations, Up: VMS - -Include Files and VMS -===================== - - Due to the differences between the filesystems of Unix and VMS, GNU -CC attempts to translate file names in `#include' into names that VMS -will understand. The basic strategy is to prepend a prefix to the -specification of the include file, convert the whole filename to a VMS -filename, and then try to open the file. GNU CC tries various prefixes -one by one until one of them succeeds: - - 1. The first prefix is the `GNU_CC_INCLUDE:' logical name: this is - where GNU C header files are traditionally stored. If you wish to - store header files in non-standard locations, then you can assign - the logical `GNU_CC_INCLUDE' to be a search list, where each - element of the list is suitable for use with a rooted logical. - - 2. The next prefix tried is `SYS$SYSROOT:[SYSLIB.]'. This is where - VAX-C header files are traditionally stored. - - 3. If the include file specification by itself is a valid VMS - filename, the preprocessor then uses this name with no prefix in - an attempt to open the include file. - - 4. If the file specification is not a valid VMS filename (i.e. does - not contain a device or a directory specifier, and contains a `/' - character), the preprocessor tries to convert it from Unix syntax - to VMS syntax. - - Conversion works like this: the first directory name becomes a - device, and the rest of the directories are converted into - VMS-format directory names. For example, the name `X11/foobar.h' - is translated to `X11:[000000]foobar.h' or `X11:foobar.h', - whichever one can be opened. This strategy allows you to assign a - logical name to point to the actual location of the header files. - - 5. If none of these strategies succeeds, the `#include' fails. - - Include directives of the form: - - #include foobar - -are a common source of incompatibility between VAX-C and GNU CC. VAX-C -treats this much like a standard `#include <foobar.h>' directive. That -is incompatible with the ANSI C behavior implemented by GNU CC: to -expand the name `foobar' as a macro. Macro expansion should eventually -yield one of the two standard formats for `#include': - - #include "FILE" - #include <FILE> - - If you have this problem, the best solution is to modify the source -to convert the `#include' directives to one of the two standard forms. -That will work with either compiler. If you want a quick and dirty fix, -define the file names as macros with the proper expansion, like this: - - #define stdio <stdio.h> - -This will work, as long as the name doesn't conflict with anything else -in the program. - - Another source of incompatibility is that VAX-C assumes that: - - #include "foobar" - -is actually asking for the file `foobar.h'. GNU CC does not make this -assumption, and instead takes what you ask for literally; it tries to -read the file `foobar'. The best way to avoid this problem is to -always specify the desired file extension in your include directives. - - GNU CC for VMS is distributed with a set of include files that is -sufficient to compile most general purpose programs. Even though the -GNU CC distribution does not contain header files to define constants -and structures for some VMS system-specific functions, there is no -reason why you cannot use GNU CC with any of these functions. You first -may have to generate or create header files, either by using the public -domain utility `UNSDL' (which can be found on a DECUS tape), or by -extracting the relevant modules from one of the system macro libraries, -and using an editor to construct a C header file. - - A `#include' file name cannot contain a DECNET node name. The -preprocessor reports an I/O error if you attempt to use a node name, -whether explicitly, or implicitly via a logical name. - - -File: gcc.info, Node: Global Declarations, Next: VMS Misc, Prev: Include Files and VMS, Up: VMS - -Global Declarations and VMS -=========================== - - GNU CC does not provide the `globalref', `globaldef' and -`globalvalue' keywords of VAX-C. You can get the same effect with an -obscure feature of GAS, the GNU assembler. (This requires GAS version -1.39 or later.) The following macros allow you to use this feature in -a fairly natural way: - - #ifdef __GNUC__ - #define GLOBALREF(TYPE,NAME) \ - TYPE NAME \ - asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME) - #define GLOBALDEF(TYPE,NAME,VALUE) \ - TYPE NAME \ - asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME) \ - = VALUE - #define GLOBALVALUEREF(TYPE,NAME) \ - const TYPE NAME[1] \ - asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME) - #define GLOBALVALUEDEF(TYPE,NAME,VALUE) \ - const TYPE NAME[1] \ - asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME) \ - = {VALUE} - #else - #define GLOBALREF(TYPE,NAME) \ - globalref TYPE NAME - #define GLOBALDEF(TYPE,NAME,VALUE) \ - globaldef TYPE NAME = VALUE - #define GLOBALVALUEDEF(TYPE,NAME,VALUE) \ - globalvalue TYPE NAME = VALUE - #define GLOBALVALUEREF(TYPE,NAME) \ - globalvalue TYPE NAME - #endif - -(The `_$$PsectAttributes_GLOBALSYMBOL' prefix at the start of the name -is removed by the assembler, after it has modified the attributes of -the symbol). These macros are provided in the VMS binaries -distribution in a header file `GNU_HACKS.H'. An example of the usage -is: - - GLOBALREF (int, ijk); - GLOBALDEF (int, jkl, 0); - - The macros `GLOBALREF' and `GLOBALDEF' cannot be used -straightforwardly for arrays, since there is no way to insert the array -dimension into the declaration at the right place. However, you can -declare an array with these macros if you first define a typedef for the -array type, like this: - - typedef int intvector[10]; - GLOBALREF (intvector, foo); - - Array and structure initializers will also break the macros; you can -define the initializer to be a macro of its own, or you can expand the -`GLOBALDEF' macro by hand. You may find a case where you wish to use -the `GLOBALDEF' macro with a large array, but you are not interested in -explicitly initializing each element of the array. In such cases you -can use an initializer like: `{0,}', which will initialize the entire -array to `0'. - - A shortcoming of this implementation is that a variable declared with -`GLOBALVALUEREF' or `GLOBALVALUEDEF' is always an array. For example, -the declaration: - - GLOBALVALUEREF(int, ijk); - -declares the variable `ijk' as an array of type `int [1]'. This is -done because a globalvalue is actually a constant; its "value" is what -the linker would normally consider an address. That is not how an -integer value works in C, but it is how an array works. So treating -the symbol as an array name gives consistent results--with the -exception that the value seems to have the wrong type. *Don't try to -access an element of the array.* It doesn't have any elements. The -array "address" may not be the address of actual storage. - - The fact that the symbol is an array may lead to warnings where the -variable is used. Insert type casts to avoid the warnings. Here is an -example; it takes advantage of the ANSI C feature allowing macros that -expand to use the same name as the macro itself. - - GLOBALVALUEREF (int, ss$_normal); - GLOBALVALUEDEF (int, xyzzy,123); - #ifdef __GNUC__ - #define ss$_normal ((int) ss$_normal) - #define xyzzy ((int) xyzzy) - #endif - - Don't use `globaldef' or `globalref' with a variable whose type is -an enumeration type; this is not implemented. Instead, make the -variable an integer, and use a `globalvaluedef' for each of the -enumeration values. An example of this would be: - - #ifdef __GNUC__ - GLOBALDEF (int, color, 0); - GLOBALVALUEDEF (int, RED, 0); - GLOBALVALUEDEF (int, BLUE, 1); - GLOBALVALUEDEF (int, GREEN, 3); - #else - enum globaldef color {RED, BLUE, GREEN = 3}; - #endif - - -File: gcc.info, Node: VMS Misc, Prev: Global Declarations, Up: VMS - -Other VMS Issues -================ - - GNU CC automatically arranges for `main' to return 1 by default if -you fail to specify an explicit return value. This will be interpreted -by VMS as a status code indicating a normal successful completion. -Version 1 of GNU CC did not provide this default. - - GNU CC on VMS works only with the GNU assembler, GAS. You need -version 1.37 or later of GAS in order to produce value debugging -information for the VMS debugger. Use the ordinary VMS linker with the -object files produced by GAS. - - Under previous versions of GNU CC, the generated code would -occasionally give strange results when linked to the sharable `VAXCRTL' -library. Now this should work. - - A caveat for use of `const' global variables: the `const' modifier -must be specified in every external declaration of the variable in all -of the source files that use that variable. Otherwise the linker will -issue warnings about conflicting attributes for the variable. Your -program will still work despite the warnings, but the variable will be -placed in writable storage. - - Although the VMS linker does distinguish between upper and lower case -letters in global symbols, most VMS compilers convert all such symbols -into upper case and most run-time library routines also have upper case -names. To be able to reliably call such routines, GNU CC (by means of -the assembler GAS) converts global symbols into upper case like other -VMS compilers. However, since the usual practice in C is to distinguish -case, GNU CC (via GAS) tries to preserve usual C behavior by augmenting -each name that is not all lower case. This means truncating the name -to at most 23 characters and then adding more characters at the end -which encode the case pattern of those 23. Names which contain at -least one dollar sign are an exception; they are converted directly into -upper case without augmentation. - - Name augmentation yields bad results for programs that use -precompiled libraries (such as Xlib) which were generated by another -compiler. You can use the compiler option `/NOCASE_HACK' to inhibit -augmentation; it makes external C functions and variables -case-independent as is usual on VMS. Alternatively, you could write -all references to the functions and variables in such libraries using -lower case; this will work on VMS, but is not portable to other -systems. The compiler option `/NAMES' also provides control over -global name handling. - - Function and variable names are handled somewhat differently with GNU -C++. The GNU C++ compiler performs "name mangling" on function names, -which means that it adds information to the function name to describe -the data types of the arguments that the function takes. One result of -this is that the name of a function can become very long. Since the -VMS linker only recognizes the first 31 characters in a name, special -action is taken to ensure that each function and variable has a unique -name that can be represented in 31 characters. - - If the name (plus a name augmentation, if required) is less than 32 -characters in length, then no special action is performed. If the name -is longer than 31 characters, the assembler (GAS) will generate a hash -string based upon the function name, truncate the function name to 23 -characters, and append the hash string to the truncated name. If the -`/VERBOSE' compiler option is used, the assembler will print both the -full and truncated names of each symbol that is truncated. - - The `/NOCASE_HACK' compiler option should not be used when you are -compiling programs that use libg++. libg++ has several instances of -objects (i.e. `Filebuf' and `filebuf') which become indistinguishable -in a case-insensitive environment. This leads to cases where you need -to inhibit augmentation selectively (if you were using libg++ and Xlib -in the same program, for example). There is no special feature for -doing this, but you can get the result by defining a macro for each -mixed case symbol for which you wish to inhibit augmentation. The -macro should expand into the lower case equivalent of itself. For -example: - - #define StuDlyCapS studlycaps - - These macro definitions can be placed in a header file to minimize -the number of changes to your source code. - - -File: gcc.info, Node: Portability, Next: Interface, Prev: VMS, Up: Top - -GNU CC and Portability -********************** - - The main goal of GNU CC was to make a good, fast compiler for -machines in the class that the GNU system aims to run on: 32-bit -machines that address 8-bit bytes and have several general registers. -Elegance, theoretical power and simplicity are only secondary. - - GNU CC gets most of the information about the target machine from a -machine description which gives an algebraic formula for each of the -machine's instructions. This is a very clean way to describe the -target. But when the compiler needs information that is difficult to -express in this fashion, I have not hesitated to define an ad-hoc -parameter to the machine description. The purpose of portability is to -reduce the total work needed on the compiler; it was not of interest -for its own sake. - - GNU CC does not contain machine dependent code, but it does contain -code that depends on machine parameters such as endianness (whether the -most significant byte has the highest or lowest address of the bytes in -a word) and the availability of autoincrement addressing. In the -RTL-generation pass, it is often necessary to have multiple strategies -for generating code for a particular kind of syntax tree, strategies -that are usable for different combinations of parameters. Often I have -not tried to address all possible cases, but only the common ones or -only the ones that I have encountered. As a result, a new target may -require additional strategies. You will know if this happens because -the compiler will call `abort'. Fortunately, the new strategies can be -added in a machine-independent fashion, and will affect only the target -machines that need them. - - -File: gcc.info, Node: Interface, Next: Passes, Prev: Portability, Up: Top - -Interfacing to GNU CC Output -**************************** - - GNU CC is normally configured to use the same function calling -convention normally in use on the target system. This is done with the -machine-description macros described (*note Target Macros::.). - - However, returning of structure and union values is done differently -on some target machines. As a result, functions compiled with PCC -returning such types cannot be called from code compiled with GNU CC, -and vice versa. This does not cause trouble often because few Unix -library routines return structures or unions. - - GNU CC code returns structures and unions that are 1, 2, 4 or 8 bytes -long in the same registers used for `int' or `double' return values. -(GNU CC typically allocates variables of such types in registers also.) -Structures and unions of other sizes are returned by storing them into -an address passed by the caller (usually in a register). The -machine-description macros `STRUCT_VALUE' and `STRUCT_INCOMING_VALUE' -tell GNU CC where to pass this address. - - By contrast, PCC on most target machines returns structures and -unions of any size by copying the data into an area of static storage, -and then returning the address of that storage as if it were a pointer -value. The caller must copy the data from that memory area to the -place where the value is wanted. This is slower than the method used -by GNU CC, and fails to be reentrant. - - On some target machines, such as RISC machines and the 80386, the -standard system convention is to pass to the subroutine the address of -where to return the value. On these machines, GNU CC has been -configured to be compatible with the standard compiler, when this method -is used. It may not be compatible for structures of 1, 2, 4 or 8 bytes. - - GNU CC uses the system's standard convention for passing arguments. -On some machines, the first few arguments are passed in registers; in -others, all are passed on the stack. It would be possible to use -registers for argument passing on any machine, and this would probably -result in a significant speedup. But the result would be complete -incompatibility with code that follows the standard convention. So this -change is practical only if you are switching to GNU CC as the sole C -compiler for the system. We may implement register argument passing on -certain machines once we have a complete GNU system so that we can -compile the libraries with GNU CC. - - On some machines (particularly the Sparc), certain types of arguments -are passed "by invisible reference". This means that the value is -stored in memory, and the address of the memory location is passed to -the subroutine. - - If you use `longjmp', beware of automatic variables. ANSI C says -that automatic variables that are not declared `volatile' have undefined -values after a `longjmp'. And this is all GNU CC promises to do, -because it is very difficult to restore register variables correctly, -and one of GNU CC's features is that it can put variables in registers -without your asking it to. - - If you want a variable to be unaltered by `longjmp', and you don't -want to write `volatile' because old C compilers don't accept it, just -take the address of the variable. If a variable's address is ever -taken, even if just to compute it and ignore it, then the variable -cannot go in a register: - - { - int careful; - &careful; - ... - } - - Code compiled with GNU CC may call certain library routines. Most of -them handle arithmetic for which there are no instructions. This -includes multiply and divide on some machines, and floating point -operations on any machine for which floating point support is disabled -with `-msoft-float'. Some standard parts of the C library, such as -`bcopy' or `memcpy', are also called automatically. The usual function -call interface is used for calling the library routines. - - These library routines should be defined in the library `libgcc.a', -which GNU CC automatically searches whenever it links a program. On -machines that have multiply and divide instructions, if hardware -floating point is in use, normally `libgcc.a' is not needed, but it is -searched just in case. - - Each arithmetic function is defined in `libgcc1.c' to use the -corresponding C arithmetic operator. As long as the file is compiled -with another C compiler, which supports all the C arithmetic operators, -this file will work portably. However, `libgcc1.c' does not work if -compiled with GNU CC, because each arithmetic function would compile -into a call to itself! - |