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GNU Info File | 1996-09-28 | 50KB | 851 lines

This is Info file gcc.info, produced by Makeinfo-1.55 from the input file gcc.texi. This file documents the use and the internals of the GNU compiler. Published by the Free Software Foundation 675 Massachusetts Avenue Cambridge, MA 02139 USA Copyright (C) 1988, 1989, 1992, 1993, 1994 Free Software Foundation, 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: Min and Max, Next: Destructors and Goto, Prev: Naming Results, Up: C++ Extensions Minimum and Maximum Operators in C++ ==================================== It is very convenient to have operators which return the "minimum" or the "maximum" of two arguments. In GNU C++ (but not in GNU C), `A <? B' is the "minimum", returning the smaller of the numeric values A and B; `A >? B' is the "maximum", returning the larger of the numeric values A and B. These operations are not primitive in ordinary C++, since you can use a macro to return the minimum of two things in C++, as in the following example. #define MIN(X,Y) ((X) < (Y) ? : (X) : (Y)) You might then use `int min = MIN (i, j);' to set MIN to the minimum value of variables I and J. However, side effects in `X' or `Y' may cause unintended behavior. For example, `MIN (i++, j++)' will fail, incrementing the smaller counter twice. A GNU C extension allows you to write safe macros that avoid this kind of problem (*note Naming an Expression's Type: Naming Types.). However, writing `MIN' and `MAX' as macros also forces you to use function-call notation notation for a fundamental arithmetic operation. Using GNU C++ extensions, you can write `int min = i <? j;' instead. Since `<?' and `>?' are built into the compiler, they properly handle expressions with side-effects; `int min = i++ <? j++;' works correctly. File: gcc.info, Node: Destructors and Goto, Next: C++ Interface, Prev: Min and Max, Up: C++ Extensions `goto' and Destructors in GNU C++ ================================= In C++ programs, you can safely use the `goto' statement. When you use it to exit a block which contains aggregates requiring destructors, the destructors will run before the `goto' transfers control. (In ANSI C++, `goto' is restricted to targets within the current block.) The compiler still forbids using `goto' to *enter* a scope that requires constructors. File: gcc.info, Node: C++ Interface, Next: Template Instantiation, Prev: Destructors and Goto, Up: C++ Extensions Declarations and Definitions in One Header ========================================== C++ object definitions can be quite complex. In principle, your source code will need two kinds of things for each object that you use across more than one source file. First, you need an "interface" specification, describing its structure with type declarations and function prototypes. Second, you need the "implementation" itself. It can be tedious to maintain a separate interface description in a header file, in parallel to the actual implementation. It is also dangerous, since separate interface and implementation definitions may not remain parallel. With GNU C++, you can use a single header file for both purposes. *Warning:* The mechanism to specify this is in transition. For the nonce, you must use one of two `#pragma' commands; in a future release of GNU C++, an alternative mechanism will make these `#pragma' commands unnecessary. The header file contains the full definitions, but is marked with `#pragma interface' in the source code. This allows the compiler to use the header file only as an interface specification when ordinary source files incorporate it with `#include'. In the single source file where the full implementation belongs, you can use either a naming convention or `#pragma implementation' to indicate this alternate use of the header file. `#pragma interface' `#pragma interface "SUBDIR/OBJECTS.h"' Use this directive in *header files* that define object classes, to save space in most of the object files that use those classes. Normally, local copies of certain information (backup copies of inline member functions, debugging information, and the internal tables that implement virtual functions) must be kept in each object file that includes class definitions. You can use this pragma to avoid such duplication. When a header file containing `#pragma interface' is included in a compilation, this auxiliary information will not be generated (unless the main input source file itself uses `#pragma implementation'). Instead, the object files will contain references to be resolved at link time. The second form of this directive is useful for the case where you have multiple headers with the same name in different directories. If you use this form, you must specify the same string to `#pragma implementation'. `#pragma implementation' `#pragma implementation "OBJECTS.h"' Use this pragma in a *main input file*, when you want full output from included header files to be generated (and made globally visible). The included header file, in turn, should use `#pragma interface'. Backup copies of inline member functions, debugging information, and the internal tables used to implement virtual functions are all generated in implementation files. If you use `#pragma implementation' with no argument, it applies to an include file with the same basename(1) as your source file. For example, in `allclass.cc', `#pragma implementation' by itself is equivalent to `#pragma implementation "allclass.h"'. In versions of GNU C++ prior to 2.6.0 `allclass.h' was treated as an implementation file whenever you would include it from `allclass.cc' even if you never specified `#pragma implementation'. This was deemed to be more trouble than it was worth, however, and disabled. If you use an explicit `#pragma implementation', it must appear in your source file *before* you include the affected header files. Use the string argument if you want a single implementation file to include code from multiple header files. (You must also use `#include' to include the header file; `#pragma implementation' only specifies how to use the file--it doesn't actually include it.) There is no way to split up the contents of a single header file into multiple implementation files. `#pragma implementation' and `#pragma interface' also have an effect on function inlining. If you define a class in a header file marked with `#pragma interface', the effect on a function defined in that class is similar to an explicit `extern' declaration--the compiler emits no code at all to define an independent version of the function. Its definition is used only for inlining with its callers. Conversely, when you include the same header file in a main source file that declares it as `#pragma implementation', the compiler emits code for the function itself; this defines a version of the function that can be found via pointers (or by callers compiled without inlining). If all calls to the function can be inlined, you can avoid emitting the function by compiling with `-fno-implement-inlines'. If any calls were not inlined, you will get linker errors. ---------- Footnotes ---------- (1) A file's "basename" was the name stripped of all leading path information and of trailing suffixes, such as `.h' or `.C' or `.cc'. File: gcc.info, Node: Template Instantiation, Next: C++ Signatures, Prev: C++ Interface, Up: C++ Extensions Where's the Template? ===================== C++ templates are the first language feature to require more intelligence from the environment than one usually finds on a UNIX system. Somehow the compiler and linker have to make sure that each template instance occurs exactly once in the executable if it is needed, and not at all otherwise. There are two basic approaches to this problem, which I will refer to as the Borland model and the Cfront model. Borland model Borland C++ solved the template instantiation problem by adding the code equivalent of common blocks to their linker; template instances are emitted in each translation unit that uses them, and they are collapsed together at run time. The advantage of this model is that the linker only has to consider the object files themselves; there is no external complexity to worry about. This disadvantage is that compilation time is increased because the template code is being compiled repeatedly. Code written for this model tends to include definitions of all member templates in the header file, since they must be seen to be compiled. Cfront model The AT&T C++ translator, Cfront, solved the template instantiation problem by creating the notion of a template repository, an automatically maintained place where template instances are stored. As individual object files are built, notes are placed in the repository to record where templates and potential type arguments were seen so that the subsequent instantiation step knows where to find them. At link time, any needed instances are generated and linked in. The advantages of this model are more optimal compilation speed and the ability to use the system linker; to implement the Borland model a compiler vendor also needs to replace the linker. The disadvantages are vastly increased complexity, and thus potential for error; theoretically, this should be just as transparent, but in practice it has been very difficult to build multiple programs in one directory and one program in multiple directories using Cfront. Code written for this model tends to separate definitions of non-inline member templates into a separate file, which is magically found by the link preprocessor when a template needs to be instantiated. Currently, g++ implements neither automatic model. The g++ team hopes to have a repository working for 2.7.0. In the mean time, you have three options for dealing with template instantiations: 1. Do nothing. Pretend g++ does implement automatic instantiation management. Code written for the Borland model will work fine, but each translation unit will contain instances of each of the templates it uses. In a large program, this can lead to an unacceptable amount of code duplication. 2. Add `#pragma interface' to all files containing template definitions. For each of these files, add `#pragma implementation "FILENAME"' to the top of some `.C' file which `#include's it. Then compile everything with -fexternal-templates. The templates will then only be expanded in the translation unit which implements them (i.e. has a `#pragma implementation' line for the file where they live); all other files will use external references. If you're lucky, everything should work properly. If you get undefined symbol errors, you need to make sure that each template instance which is used in the program is used in the file which implements that template. If you don't have any use for a particular instance in that file, you can just instantiate it explicitly, using the syntax from the latest C++ working paper: template class A<int>; template ostream& operator << (ostream&, const A<int>&); This strategy will work with code written for either model. If you are using code written for the Cfront model, the file containing a class template and the file containing its member templates should be implemented in the same translation unit. A slight variation on this approach is to use the flag -falt-external-templates instead; this flag causes template instances to be emitted in the translation unit that implements the header where they are first instantiated, rather than the one which implements the file where the templates are defined. This header must be the same in all translation units, or things are likely to break. *Note Declarations and Definitions in One Header: C++ Interface, for more discussion of these pragmas. 3. Explicitly instantiate all the template instances you use, and compile with -fno-implicit-templates. This is probably your best bet; it may require more knowledge of exactly which templates you are using, but it's less mysterious than the previous approach, and it doesn't require any `#pragma's or other g++-specific code. You can scatter the instantiations throughout your program, you can create one big file to do all the instantiations, or you can create tiny files like #include "Foo.h" #include "Foo.cc" template class Foo<int>; for each instance you need, and create a template instantiation library from those. I'm partial to the last, but your mileage may vary. If you are using Cfront-model code, you can probably get away with not using -fno-implicit-templates when compiling files that don't `#include' the member template definitions. File: gcc.info, Node: C++ Signatures, Prev: Template Instantiation, Up: C++ Extensions Type Abstraction using Signatures ================================= In GNU C++, you can use the keyword `signature' to define a completely abstract class interface as a datatype. You can connect this abstraction with actual classes using signature pointers. If you want to use signatures, run the GNU compiler with the `-fhandle-signatures' command-line option. (With this option, the compiler reserves a second keyword `sigof' as well, for a future extension.) Roughly, signatures are type abstractions or interfaces of classes. Some other languages have similar facilities. C++ signatures are related to ML's signatures, Haskell's type classes, definition modules in Modula-2, interface modules in Modula-3, abstract types in Emerald, type modules in Trellis/Owl, categories in Scratchpad II, and types in POOL-I. For a more detailed discussion of signatures, see `Signatures: A C++ Extension for Type Abstraction and Subtype Polymorphism' by Gerald Baumgartner and Vincent F. Russo (Tech report CSD-TR-93-059, Dept. of Computer Sciences, Purdue University, September 1993, to appear in *Software Practice & Experience*). You can get the tech report by anonymous FTP from `ftp.cs.purdue.edu' in `pub/reports/TR93-059.PS.Z'. Syntactically, a signature declaration is a collection of member function declarations and nested type declarations. For example, this signature declaration defines a new abstract type `S' with member functions `int foo ()' and `int bar (int)': signature S { int foo (); int bar (int); }; Since signature types do not include implementation definitions, you cannot write an instance of a signature directly. Instead, you can define a pointer to any class that contains the required interfaces as a "signature pointer". Such a class "implements" the signature type. To use a class as an implementation of `S', you must ensure that the class has public member functions `int foo ()' and `int bar (int)'. The class can have other member functions as well, public or not; as long as it offers what's declared in the signature, it is suitable as an implementation of that signature type. For example, suppose that `C' is a class that meets the requirements of signature `S' (`C' "conforms to" `S'). Then C obj; S * p = &obj; defines a signature pointer `p' and initializes it to point to an object of type `C'. The member function call `int i = p->foo ();' executes `obj.foo ()'. Abstract virtual classes provide somewhat similar facilities in standard C++. There are two main advantages to using signatures instead: 1. Subtyping becomes independent from inheritance. A class or signature type `T' is a subtype of a signature type `S' independent of any inheritance hierarchy as long as all the member functions declared in `S' are also found in `T'. So you can define a subtype hierarchy that is completely independent from any inheritance (implementation) hierarchy, instead of being forced to use types that mirror the class inheritance hierarchy. 2. Signatures allow you to work with existing class hierarchies as implementations of a signature type. If those class hierarchies are only available in compiled form, you're out of luck with abstract virtual classes, since an abstract virtual class cannot be retrofitted on top of existing class hierarchies. So you would be required to write interface classes as subtypes of the abstract virtual class. There is one more detail about signatures. A signature declaration can contain member function *definitions* as well as member function declarations. A signature member function with a full definition is called a *default implementation*; classes need not contain that particular interface in order to conform. For example, a class `C' can conform to the signature signature T { int f (int); int f0 () { return f (0); }; }; whether or not `C' implements the member function `int f0 ()'. If you define `C::f0', that definition takes precedence; otherwise, the default implementation `S::f0' applies. File: gcc.info, Node: Trouble, Next: Bugs, Prev: C++ Extensions, Up: Top Known Causes of Trouble with GNU CC *********************************** This section describes known problems that affect users of GNU CC. Most of these are not GNU CC bugs per se--if they were, we would fix them. But the result for a user may be like the result of a bug. Some of these problems are due to bugs in other software, some are missing features that are too much work to add, and some are places where people's opinions differ as to what is best. * Menu: * Actual Bugs:: Bugs we will fix later. * Installation Problems:: Problems that manifest when you install GNU CC. * Cross-Compiler Problems:: Common problems of cross compiling with GNU CC. * Interoperation:: Problems using GNU CC with other compilers, and with certain linkers, assemblers and debuggers. * External Bugs:: Problems compiling certain programs. * Incompatibilities:: GNU CC is incompatible with traditional C. * Fixed Headers:: GNU C uses corrected versions of system header files. This is necessary, but doesn't always work smoothly. * Disappointments:: Regrettable things we can't change, but not quite bugs. * C++ Misunderstandings:: Common misunderstandings with GNU C++. * Protoize Caveats:: Things to watch out for when using `protoize'. * Non-bugs:: Things we think are right, but some others disagree. * Warnings and Errors:: Which problems in your code get warnings, and which get errors. File: gcc.info, Node: Actual Bugs, Next: Installation Problems, Up: Trouble Actual Bugs We Haven't Fixed Yet ================================ * The `fixincludes' script interacts badly with automounters; if the directory of system header files is automounted, it tends to be unmounted while `fixincludes' is running. This would seem to be a bug in the automounter. We don't know any good way to work around it. * The `fixproto' script will sometimes add prototypes for the `sigsetjmp' and `siglongjmp' functions that reference the `jmp_buf' type before that type is defined. To work around this, edit the offending file and place the typedef in front of the prototypes. * There are several obscure case of mis-using struct, union, and enum tags that are not detected as errors by the compiler. * When `-pedantic-errors' is specified, GNU C will incorrectly give an error message when a function name is specified in an expression involving the comma operator. * Loop unrolling doesn't work properly for certain C++ programs. This is a bug in the C++ front end. It sometimes emits incorrect debug info, and the loop unrolling code is unable to recover from this error. File: gcc.info, Node: Installation Problems, Next: Cross-Compiler Problems, Prev: Actual Bugs, Up: Trouble Installation Problems ===================== This is a list of problems (and some apparent problems which don't really mean anything is wrong) that show up during installation of GNU * On certain systems, defining certain environment variables such as `CC' can interfere with the functioning of `make'. * If you encounter seemingly strange errors when trying to build the compiler in a directory other than the source directory, it could be because you have previously configured the compiler in the source directory. Make sure you have done all the necessary preparations. *Note Other Dir::. * If you build GNU CC on a BSD system using a directory stored in a System V file system, problems may occur in running `fixincludes' if the System V file system doesn't support symbolic links. These problems result in a failure to fix the declaration of `size_t' in `sys/types.h'. If you find that `size_t' is a signed type and that type mismatches occur, this could be the cause. The solution is not to use such a directory for building GNU CC. * In previous versions of GNU CC, the `gcc' driver program looked for `as' and `ld' in various places; for example, in files beginning with `/usr/local/lib/gcc-'. GNU CC version 2 looks for them in the directory `/usr/local/lib/gcc-lib/TARGET/VERSION'. Thus, to use a version of `as' or `ld' that is not the system default, for example `gas' or GNU `ld', you must put them in that directory (or make links to them from that directory). * Some commands executed when making the compiler may fail (return a non-zero status) and be ignored by `make'. These failures, which are often due to files that were not found, are expected, and can safely be ignored. * It is normal to have warnings in compiling certain files about unreachable code and about enumeration type clashes. These files' names begin with `insn-'. Also, `real.c' may get some warnings that you can ignore. * Sometimes `make' recompiles parts of the compiler when installing the compiler. In one case, this was traced down to a bug in `make'. Either ignore the problem or switch to GNU Make. * If you have installed a program known as purify, you may find that it causes errors while linking `enquire', which is part of building GNU CC. The fix is to get rid of the file `real-ld' which purify installs--so that GNU CC won't try to use it. * On Linux SLS 1.01, there is a problem with `libc.a': it does not contain the obstack functions. However, GNU CC assumes that the obstack functions are in `libc.a' when it is the GNU C library. To work around this problem, change the `__GNU_LIBRARY__' conditional around line 31 to `#if 1'. * On some 386 systems, building the compiler never finishes because `enquire' hangs due to a hardware problem in the motherboard--it reports floating point exceptions to the kernel incorrectly. You can install GNU CC except for `float.h' by patching out the command to run `enquire'. You may also be able to fix the problem for real by getting a replacement motherboard. This problem was observed in Revision E of the Micronics motherboard, and is fixed in Revision F. It has also been observed in the MYLEX MXA-33 motherboard. If you encounter this problem, you may also want to consider removing the FPU from the socket during the compilation. Alternatively, if you are running SCO Unix, you can reboot and force the FPU to be ignored. To do this, type `hd(40)unix auto ignorefpu'. * On some 386 systems, GNU CC crashes trying to compile `enquire.c'. This happens on machines that don't have a 387 FPU chip. On 386 machines, the system kernel is supposed to emulate the 387 when you don't have one. The crash is due to a bug in the emulator. One of these systems is the Unix from Interactive Systems: 386/ix. On this system, an alternate emulator is provided, and it does work. To use it, execute this command as super-user: ln /etc/emulator.rel1 /etc/emulator and then reboot the system. (The default emulator file remains present under the name `emulator.dflt'.) Try using `/etc/emulator.att', if you have such a problem on the SCO system. Another system which has this problem is Esix. We don't know whether it has an alternate emulator that works. On NetBSD 0.8, a similar problem manifests itself as these error messages: enquire.c: In function `fprop': enquire.c:2328: floating overflow * On SCO systems, when compiling GNU CC with the system's compiler, do not use `-O'. Some versions of the system's compiler miscompile GNU CC with `-O'. * Sometimes on a Sun 4 you may observe a crash in the program `genflags' or `genoutput' while building GNU CC. This is said to be due to a bug in `sh'. You can probably get around it by running `genflags' or `genoutput' manually and then retrying the `make'. * On Solaris 2, executables of GNU CC version 2.0.2 are commonly available, but they have a bug that shows up when compiling current versions of GNU CC: undefined symbol errors occur during assembly if you use `-g'. The solution is to compile the current version of GNU CC without `-g'. That makes a working compiler which you can use to recompile with `-g'. * Solaris 2 comes with a number of optional OS packages. Some of these packages are needed to use GNU CC fully. If you did not install all optional packages when installing Solaris, you will need to verify that the packages that GNU CC needs are installed. To check whether an optional package is installed, use the `pkginfo' command. To add an optional package, use the `pkgadd' command. For further details, see the Solaris documentation. For Solaris 2.0 and 2.1, GNU CC needs six packages: `SUNWarc', `SUNWbtool', `SUNWesu', `SUNWhea', `SUNWlibm', and `SUNWtoo'. For Solaris 2.2, GNU CC needs an additional seventh package: `SUNWsprot'. * On Solaris 2, trying to use the linker and other tools in `/usr/ucb' to install GNU CC has been observed to cause trouble. For example, the linker may hang indefinitely. The fix is to remove `/usr/ucb' from your `PATH'. * If you use the 1.31 version of the MIPS assembler (such as was shipped with Ultrix 3.1), you will need to use the -fno-delayed-branch switch when optimizing floating point code. Otherwise, the assembler will complain when the GCC compiler fills a branch delay slot with a floating point instruction, such as `add.d'. * If on a MIPS system you get an error message saying "does not have gp sections for all it's [sic] sectons [sic]", don't worry about it. This happens whenever you use GAS with the MIPS linker, but there is not really anything wrong, and it is okay to use the output file. You can stop such warnings by installing the GNU linker. It would be nice to extend GAS to produce the gp tables, but they are optional, and there should not be a warning about their absence. * In Ultrix 4.0 on the MIPS machine, `stdio.h' does not work with GNU CC at all unless it has been fixed with `fixincludes'. This causes problems in building GNU CC. Once GNU CC is installed, the problems go away. To work around this problem, when making the stage 1 compiler, specify this option to Make: GCC_FOR_TARGET="./xgcc -B./ -I./include" When making stage 2 and stage 3, specify this option: CFLAGS="-g -I./include" * Users have reported some problems with version 2.0 of the MIPS compiler tools that were shipped with Ultrix 4.1. Version 2.10 which came with Ultrix 4.2 seems to work fine. Users have also reported some problems with version 2.20 of the MIPS compiler tools that were shipped with RISC/os 4.x. The earlier version 2.11 seems to work fine. * Some versions of the MIPS linker will issue an assertion failure when linking code that uses `alloca' against shared libraries on RISC-OS 5.0, and DEC's OSF/1 systems. This is a bug in the linker, that is supposed to be fixed in future revisions. To protect against this, GNU CC passes `-non_shared' to the linker unless you pass an explicit `-shared' or `-call_shared' switch. * On System V release 3, you may get this error message while linking: ld fatal: failed to write symbol name SOMETHING in strings table for file WHATEVER This probably indicates that the disk is full or your ULIMIT won't allow the file to be as large as it needs to be. This problem can also result because the kernel parameter `MAXUMEM' is too small. If so, you must regenerate the kernel and make the value much larger. The default value is reported to be 1024; a value of 32768 is said to work. Smaller values may also work. * On System V, if you get an error like this, /usr/local/lib/bison.simple: In function `yyparse': /usr/local/lib/bison.simple:625: virtual memory exhausted that too indicates a problem with disk space, ULIMIT, or `MAXUMEM'. * Current GNU CC versions probably do not work on version 2 of the NeXT operating system. * On NeXTStep 3.0, the Objective C compiler does not work, due, apparently, to a kernel bug that it happens to trigger. This problem does not happen on 3.1. * On the Tower models 4N0 and 6N0, by default a process is not allowed to have more than one megabyte of memory. GNU CC cannot compile itself (or many other programs) with `-O' in that much memory. To solve this problem, reconfigure the kernel adding the following line to the configuration file: MAXUMEM = 4096 * On HP 9000 series 300 or 400 running HP-UX release 8.0, there is a bug in the assembler that must be fixed before GNU CC can be built. This bug manifests itself during the first stage of compilation, while building `libgcc2.a': _floatdisf cc1: warning: `-g' option not supported on this version of GCC cc1: warning: `-g1' option not supported on this version of GCC ./xgcc: Internal compiler error: program as got fatal signal 11 A patched version of the assembler is available by anonymous ftp from `altdorf.ai.mit.edu' as the file `archive/cph/hpux-8.0-assembler'. If you have HP software support, the patch can also be obtained directly from HP, as described in the following note: This is the patched assembler, to patch SR#1653-010439, where the assembler aborts on floating point constants. The bug is not really in the assembler, but in the shared library version of the function "cvtnum(3c)". The bug on "cvtnum(3c)" is SR#4701-078451. Anyway, the attached assembler uses the archive library version of "cvtnum(3c)" and thus does not exhibit the bug. This patch is also known as PHCO_4484. * On HP-UX version 8.05, but not on 8.07 or more recent versions, the `fixproto' shell script triggers a bug in the system shell. If you encounter this problem, upgrade your operating system or use BASH (the GNU shell) to run `fixproto'. * Some versions of the Pyramid C compiler are reported to be unable to compile GNU CC. You must use an older version of GNU CC for bootstrapping. One indication of this problem is if you get a crash when GNU CC compiles the function `muldi3' in file `libgcc2.c'. You may be able to succeed by getting GNU CC version 1, installing it, and using it to compile GNU CC version 2. The bug in the Pyramid C compiler does not seem to affect GNU CC version 1. * There may be similar problems on System V Release 3.1 on 386 systems. * On the Intel Paragon (an i860 machine), if you are using operating system version 1.0, you will get warnings or errors about redefinition of `va_arg' when you build GNU CC. If this happens, then you need to link most programs with the library `iclib.a'. You must also modify `stdio.h' as follows: before the lines #if defined(__i860__) && !defined(_VA_LIST) #include <va_list.h> insert the line #if __PGC__ and after the lines extern int vprintf(const char *, va_list ); extern int vsprintf(char *, const char *, va_list ); #endif insert the line #endif /* __PGC__ */ These problems don't exist in operating system version 1.1. * On the Altos 3068, programs compiled with GNU CC won't work unless you fix a kernel bug. This happens using system versions V.2.2 1.0gT1 and V.2.2 1.0e and perhaps later versions as well. See the file `README.ALTOS'. * You will get several sorts of compilation and linking errors on the we32k if you don't follow the special instructions. *Note Configurations::. * A bug in the HP-UX 8.05 (and earlier) shell will cause the fixproto program to report an error of the form: ./fixproto: sh internal 1K buffer overflow To fix this, change the first line of the fixproto script to look like: #!/bin/ksh File: gcc.info, Node: Cross-Compiler Problems, Next: Interoperation, Prev: Installation Problems, Up: Trouble Cross-Compiler Problems ======================= You may run into problems with cross compilation on certain machines, for several reasons. * Cross compilation can run into trouble for certain machines because some target machines' assemblers require floating point numbers to be written as *integer* constants in certain contexts. The compiler writes these integer constants by examining the floating point value as an integer and printing that integer, because this is simple to write and independent of the details of the floating point representation. But this does not work if the compiler is running on a different machine with an incompatible floating point format, or even a different byte-ordering. In addition, correct constant folding of floating point values requires representing them in the target machine's format. (The C standard does not quite require this, but in practice it is the only way to win.) It is now possible to overcome these problems by defining macros such as `REAL_VALUE_TYPE'. But doing so is a substantial amount of work for each target machine. *Note Cross-compilation::. * At present, the program `mips-tfile' which adds debug support to object files on MIPS systems does not work in a cross compile environment. File: gcc.info, Node: Interoperation, Next: External Bugs, Prev: Cross-Compiler Problems, Up: Trouble Interoperation ============== This section lists various difficulties encountered in using GNU C or GNU C++ together with other compilers or with the assemblers, linkers, libraries and debuggers on certain systems. * Objective C does not work on the RS/6000. * GNU C++ does not do name mangling in the same way as other C++ compilers. This means that object files compiled with one compiler cannot be used with another. This effect is intentional, to protect you from more subtle problems. Compilers differ as to many internal details of C++ implementation, including: how class instances are laid out, how multiple inheritance is implemented, and how virtual function calls are handled. If the name encoding were made the same, your programs would link against libraries provided from other compilers--but the programs would then crash when run. Incompatible libraries are then detected at link time, rather than at run time. * Older GDB versions sometimes fail to read the output of GNU CC version 2. If you have trouble, get GDB version 4.4 or later. * DBX rejects some files produced by GNU CC, though it accepts similar constructs in output from PCC. Until someone can supply a coherent description of what is valid DBX input and what is not, there is nothing I can do about these problems. You are on your own. * The GNU assembler (GAS) does not support PIC. To generate PIC code, you must use some other assembler, such as `/bin/as'. * On some BSD systems, including some versions of Ultrix, use of profiling causes static variable destructors (currently used only in C++) not to be run. * Use of `-I/usr/include' may cause trouble. Many systems come with header files that won't work with GNU CC unless corrected by `fixincludes'. The corrected header files go in a new directory; GNU CC searches this directory before `/usr/include'. If you use `-I/usr/include', this tells GNU CC to search `/usr/include' earlier on, before the corrected headers. The result is that you get the uncorrected header files. Instead, you should use these options (when compiling C programs): -I/usr/local/lib/gcc-lib/TARGET/VERSION/include -I/usr/include For C++ programs, GNU CC also uses a special directory that defines C++ interfaces to standard C subroutines. This directory is meant to be searched *before* other standard include directories, so that it takes precedence. If you are compiling C++ programs and specifying include directories explicitly, use this option first, then the two options above: -I/usr/local/lib/g++-include * On some SGI systems, when you use `-lgl_s' as an option, it gets translated magically to `-lgl_s -lX11_s -lc_s'. Naturally, this does not happen when you use GNU CC. You must specify all three options explicitly. * On a Sparc, GNU CC aligns all values of type `double' on an 8-byte boundary, and it expects every `double' to be so aligned. The Sun compiler usually gives `double' values 8-byte alignment, with one exception: function arguments of type `double' may not be aligned. As a result, if a function compiled with Sun CC takes the address of an argument of type `double' and passes this pointer of type `double *' to a function compiled with GNU CC, dereferencing the pointer may cause a fatal signal. One way to solve this problem is to compile your entire program with GNU CC. Another solution is to modify the function that is compiled with Sun CC to copy the argument into a local variable; local variables are always properly aligned. A third solution is to modify the function that uses the pointer to dereference it via the following function `access_double' instead of directly with `*': inline double access_double (double *unaligned_ptr) { union d2i { double d; int i[2]; }; union d2i *p = (union d2i *) unaligned_ptr; union d2i u; u.i[0] = p->i[0]; u.i[1] = p->i[1]; return u.d; } Storing into the pointer can be done likewise with the same union. * On Solaris, the `malloc' function in the `libmalloc.a' library may allocate memory that is only 4 byte aligned. Since GNU CC on the Sparc assumes that doubles are 8 byte aligned, this may result in a fatal signal if doubles are stored in memory allocated by the `libmalloc.a' library. The solution is to not use the `libmalloc.a' library. Use instead `malloc' and related functions from `libc.a'; they do not have this problem. * Sun forgot to include a static version of `libdl.a' with some versions of SunOS (mainly 4.1). This results in undefined symbols when linking static binaries (that is, if you use `-static'). If you see undefined symbols `_dlclose', `_dlsym' or `_dlopen' when linking, compile and link against the file `mit/util/misc/dlsym.c' from the MIT version of X windows. * The 128-bit long double format that the Sparc port supports currently works by using the architecturally defined quad-word floating point instructions. Since there is no hardware that supports these instructions they must be emulated by the operating system. Long doubles do not work in Sun OS versions 4.0.3 and earlier, because the kernel eumulator uses an obsolete and incompatible format. Long doubles do not work in Sun OS versions 4.1.1 to 4.1.3 because of emululator bugs that cause random unpredicatable failures. Long doubles appear to work in Sun OS 5.x (Solaris 2.x). * On HP-UX version 9.01 on the HP PA, the HP compiler `cc' does not compile GNU CC correctly. We do not yet know why. However, GNU CC compiled on earlier HP-UX versions works properly on HP-UX 9.01 and can compile itself properly on 9.01. * On the HP PA machine, ADB sometimes fails to work on functions compiled with GNU CC. Specifically, it fails to work on functions that use `alloca' or variable-size arrays. This is because GNU CC doesn't generate HP-UX unwind descriptors for such functions. It may even be impossible to generate them. * Debugging (`-g') is not supported on the HP PA machine, unless you use the preliminary GNU tools (*note Installation::.). * Taking the address of a label may generate errors from the HP-UX PA assembler. GAS for the PA does not have this problem. * Using floating point parameters for indirect calls to static functions will not work when using the HP assembler. There simply is no way for GCC to specify what registers hold arguments for static functions when using the HP assembler. GAS for the PA does not have this problem. * For some very large functions you may receive errors from the HP linker complaining about an out of bounds unconditional branch offset. Fixing this problem correctly requires fixing problems in GNU CC and GAS. We hope to fix this in time for GNU CC 2.6. Until then you can work around by making your function smaller, and if you are using GAS, splitting the function into multiple source files may be necessary. * GNU CC compiled code sometimes emits warnings from the HP-UX assembler of the form: (warning) Use of GR3 when frame >= 8192 may cause conflict. These warnings are harmless and can be safely ignored. * The current version of the assembler (`/bin/as') for the RS/6000 has certain problems that prevent the `-g' option in GCC from working. Note that `Makefile.in' uses `-g' by default when compiling `libgcc2.c'. IBM has produced a fixed version of the assembler. The upgraded assembler unfortunately was not included in any of the AIX 3.2 update PTF releases (3.2.2, 3.2.3, or 3.2.3e). Users of AIX 3.1 should request PTF U403044 from IBM and users of AIX 3.2 should request PTF U416277. See the file `README.RS6000' for more details on these updates. You can test for the presense of a fixed assembler by using the command as -u < /dev/null If the command exits normally, the assembler fix already is installed. If the assembler complains that "-u" is an unknown flag, you need to order the fix. * On the IBM RS/6000, compiling code of the form extern int foo; ... foo ... static int foo; will cause the linker to report an undefined symbol `foo'. Although this behavior differs from most other systems, it is not a bug because redefining an `extern' variable as `static' is undefined in ANSI C. * AIX on the RS/6000 provides support (NLS) for environments outside of the United States. Compilers and assemblers use NLS to support locale-specific representations of various objects including floating-point numbers ("." vs "," for separating decimal fractions). There have been problems reported where the library linked with GCC does not produce the same floating-point formats that the assembler accepts. If you have this problem, set the LANG environment variable to "C" or "En_US". * Even if you specify `-fdollars-in-identifiers', you cannot successfully use `$' in identifiers on the RS/6000 due to a restriction in the IBM assembler. GAS supports these identifiers. * On the RS/6000, XLC version 1.3.0.0 will miscompile `jump.c'. XLC version 1.3.0.1 or later fixes this problem. You can obtain XLC-1.3.0.2 by requesting PTF 421749 from IBM. * There is an assembler bug in versions of DG/UX prior to 5.4.2.01 that occurs when the `fldcr' instruction is used. GNU CC uses `fldcr' on the 88100 to serialize volatile memory references. Use the option `-mno-serialize-volatile' if your version of the assembler has this bug. * On VMS, GAS versions 1.38.1 and earlier may cause spurious warning messages from the linker. These warning messages complain of mismatched psect attributes. You can ignore them. *Note VMS Install::. * On NewsOS version 3, if you include both of the files `stddef.h' and `sys/types.h', you get an error because there are two typedefs of `size_t'. You should change `sys/types.h' by adding these lines around the definition of `size_t': #ifndef _SIZE_T #define _SIZE_T ACTUAL TYPEDEF HERE #endif * On the Alliant, the system's own convention for returning structures and unions is unusual, and is not compatible with GNU CC no matter what options are used. * On the IBM RT PC, the MetaWare HighC compiler (hc) uses a different convention for structure and union returning. Use the option `-mhc-struct-return' to tell GNU CC to use a convention compatible with it. * On Ultrix, the Fortran compiler expects registers 2 through 5 to be saved by function calls. However, the C compiler uses conventions compatible with BSD Unix: registers 2 through 5 may be clobbered by function calls. GNU CC uses the same convention as the Ultrix C compiler. You can use these options to produce code compatible with the Fortran compiler: -fcall-saved-r2 -fcall-saved-r3 -fcall-saved-r4 -fcall-saved-r5 * On the WE32k, you may find that programs compiled with GNU CC do not work with the standard shared C ilbrary. You may need to link with the ordinary C compiler. If you do so, you must specify the following options: -L/usr/local/lib/gcc-lib/we32k-att-sysv/2.6.0 -lgcc -lc_s The first specifies where to find the library `libgcc.a' specified with the `-lgcc' option. GNU CC does linking by invoking `ld', just as `cc' does, and there is no reason why it *should* matter which compilation program you use to invoke `ld'. If someone tracks this problem down, it can probably be fixed easily. * On the Alpha, you may get assembler errors about invalid syntax as a result of floating point constants. This is due to a bug in the C library functions `ecvt', `fcvt' and `gcvt'. Given valid floating point numbers, they sometimes print `NaN'. * On Irix 4.0.5F (and perhaps in some other versions), an assembler bug sometimes reorders instructions incorrectly when optimization is turned on. If you think this may be happening to you, try using the GNU assembler; GAS version 2.1 supports ECOFF on Irix. Or use the `-noasmopt' option when you compile GNU CC with itself, and then again when you compile your program. (This is a temporary kludge to turn off assembler optimization on Irix.) If this proves to be what you need, edit the assembler spec in the file `specs' so that it unconditionally passes `-O0' to the assembler, and never passes `-O2' or `-O3'.