+++ /dev/null
-
- GCC Frequently Asked Questions
-
- The latest version of this document is always available at
- [1]http://gcc.gnu.org/faq.html.
-
- This FAQ tries to answer specific questions concerning GCC. For
- general information regarding C, C++, resp. Fortran please check the
- [2]comp.lang.c FAQ, [3]comp.std.c++ FAQ, and the [4]Fortran
- Information page.
-
- Other GCC-related FAQs: [5]libstdc++-v3, and [6]GCJ.
- _________________________________________________________________
-
- Questions
-
- 1. [7]General information
- 1. [8]What is the relationship between GCC and EGCS?
- 2. [9]What is the relationship between GCC and Cygnus / Red Hat?
- 3. [10]What is an open development model?
- 4. [11]How do I report a bug?
- 5. [12]How do I get a bug fixed or a feature added?
- 6. [13]Does GCC work on my platform?
- 2. [14]Installation
- 1. [15]How to install multiple versions of GCC
- 2. [16]Dynamic linker is unable to find GCC libraries
- 3. [17]libstdc++/libio tests fail badly with --enable-shared
- 4. [18]GCC can not find GNU as/GNU ld
- 5. [19]cpp: Usage:... Error
- 6. [20]Optimizing the compiler itself
- 3. [21]Testsuite problems
- 1. [22]Unable to run the testsuite
- 2. [23]How do I pass flags like -fnew-abi to the testsuite?
- 3. [24]How can I run the test suite with multiple options?
- 4. [25]Older versions of GCC
- 1. [26]Is there a stringstream / sstream for GCC 2.95.2?
- 5. [27]Miscellaneous
- 1. [28]Friend Templates
- 2. [29]dynamic_cast, throw, typeid don't work with shared
- libraries
- 3. [30]Why do I need autoconf, bison, xgettext, automake, etc?
- 4. [31]Why can't I build a shared library?
- 5. [32]When building C++, the linker says my constructors,
- destructors or virtual tables are undefined, but I defined
- them
- 6. [33]Will GCC someday include an incremental linker?
- _________________________________________________________________
-
- General information
-
-What is the relationship between GCC and EGCS?
-
- In 1990/1991 gcc version 1 had reached a point of stability. For the
- targets it could support, it worked well. It had limitations inherent
- in its design that would be difficult to resolve, so a major effort
- was made to resolve those limitiations and gcc version 2 was the
- result.
-
- When we had gcc2 in a useful state, development efforts on gcc1
- stopped and we all concentrated on making gcc2 better than gcc1 could
- ever be. This is the kind of step forward we wanted to make with the
- EGCS project when it was formed in 1997.
-
- In April 1999 the Free Software Foundation officially halted
- development on the gcc2 compiler and appointed the EGCS project as the
- official GCC maintainers. The net result was a single project which
- carries forward GCC development under the ultimate control of the
- [34]GCC Steering Committee.
- _________________________________________________________________
-
-What is the relationship between GCC and Cygnus / Red Hat?
-
- It is a common mis-conception that Red Hat controls GCC either
- directly or indirectly.
-
- While Red Hat does donate hardware, network connections, code and
- developer time to GCC development, Red Hat does not control GCC.
-
- Overall control of GCC is in the hands of the [35]GCC Steering
- Committee which includes people from a variety of different
- organizations and backgrounds. The purpose of the steering committee
- is to make decisions in the best interest of GCC and to help ensure
- that no individual or company has control over the project.
-
- To summarize, Red Hat contributes to the GCC project, but does not
- exert a controlling influence over GCC.
- _________________________________________________________________
-
-What is an open development model?
-
- We are using a bazaar style [36][1] approach to GCC development: we
- make snapshots publicly available to anyone who wants to try them; we
- welcome anyone to join the development mailing list. All of the
- discussions on the development mailing list are available via the web.
- We're going to be making releases with a much higher frequency than
- they have been made in the past.
-
- In addition to weekly snapshots of the GCC development sources, we
- have the sources readable from a CVS server by anyone. Furthermore we
- are using remote CVS to allow remote maintainers write access to the
- sources.
-
- There have been many potential GCC developers who were not able to
- participate in GCC development in the past. We want these people to
- help in any way they can; we ultimately want GCC to be the best
- compiler in the world.
-
- A compiler is a complicated piece of software, there will still be
- strong central maintainers who will reject patches, who will demand
- documentation of implementations, and who will keep the level of
- quality as high as it is today. Code that could use wider testing may
- be integrated--code that is simply ill-conceived won't be.
-
- GCC is not the first piece of software to use this open development
- process; FreeBSD, the Emacs lisp repository, and the Linux kernel are
- a few examples of the bazaar style of development.
-
- With GCC, we are adding new features and optimizations at a rate that
- has not been done since the creation of gcc2; these additions
- inevitably have a temporarily destabilizing effect. With the help of
- developers working together with this bazaar style development, the
- resulting stability and quality levels will be better than we've had
- before.
-
- [1] We've been discussing different development models a lot over
- the past few months. The paper which started all of this introduced
- two terms: A cathedral development model versus a bazaar
- development model. The paper is written by Eric S. Raymond, it is
- called ``The Cathedral and the Bazaar''. The paper is a useful
- starting point for discussions.
- _________________________________________________________________
-
-How do I report a bug?
-
- There are complete instructions [37]here.
- _________________________________________________________________
-
-How do I get a bug fixed or a feature added?
-
- There are lots of ways to get something fixed. The list below may be
- incomplete, but it covers many of the common cases. These are listed
- roughly in order of increasing difficulty for the average GCC user,
- meaning someone who is not skilled in the internals of GCC, and where
- difficulty is measured in terms of the time required to fix the bug.
- No alternative is better than any other; each has its benefits and
- disadvantages.
- * Hire someone to fix it for you. There are various companies and
- individuals providing support for GCC. This alternative costs
- money, but is relatively likely to get results.
- * [38]Report the problem to the GCC GNATS bug tracking system and
- hope that someone will be kind enough to fix it for you. While
- this is certainly possible, and often happens, there is no
- guarantee that it will. You should not expect the same response
- from this method that you would see from a commercial support
- organization since the people who read GCC bug reports, if they
- choose to help you, will be volunteering their time. This
- alternative will work best if you follow the directions on
- [39]submitting bugreports.
- * Fix it yourself. This alternative will probably bring results, if
- you work hard enough, but will probably take a lot of time, and,
- depending on the quality of your work and the perceived benefits
- of your changes, your code may or may not ever make it into an
- official release of GCC.
- _________________________________________________________________
-
-Does GCC work on my platform?
-
- The host/target specific installation notes for GCC include
- information about known problems with installing or using GCC on
- particular platforms. These are included in the sources for a release
- in INSTALL/specific.html, and the [40]latest version is always
- available at the GCC web site. Reports of [41]successful builds for
- several versions of GCC are also available at the web site.
- _________________________________________________________________
-
- Installation
-
-How to install multiple versions of GCC
-
- It may be desirable to install multiple versions of the compiler on
- the same system. This can be done by using different prefix paths at
- configure time and a few symlinks.
-
- Basically, configure the two compilers with different --prefix
- options, then build and install each compiler. Assume you want "gcc"
- to be the latest compiler and available in /usr/local/bin; also assume
- that you want "gcc2" to be the older gcc2 compiler and also available
- in /usr/local/bin.
-
- The easiest way to do this is to configure the new GCC with
- --prefix=/usr/local/gcc and the older gcc2 with
- --prefix=/usr/local/gcc2. Build and install both compilers. Then make
- a symlink from /usr/local/bin/gcc to /usr/local/gcc/bin/gcc and from
- /usr/local/bin/gcc2 to /usr/local/gcc2/bin/gcc. Create similar links
- for the "g++", "c++" and "g77" compiler drivers.
-
- An alternative to using symlinks is to configure with a
- --program-transform-name option. This option specifies a sed command
- to process installed program names with. Using it you can, for
- instance, have all the new GCC programs installed as "new-gcc" and the
- like. You will still have to specify different --prefix options for
- new GCC and old GCC, because it is only the executable program names
- that are transformed. The difference is that you (as administrator) do
- not have to set up symlinks, but must specify additional directories
- in your (as a user) PATH. A complication with --program-transform-name
- is that the sed command invariably contains characters significant to
- the shell, and these have to be escaped correctly, also it is not
- possible to use "^" or "$" in the command. Here is the option to
- prefix "new-" to the new GCC installed programs:
-
- --program-transform-name='s,\\\\(.*\\\\),new-\\\\1,'
-
- With the above --prefix option, that will install the new GCC programs
- into /usr/local/gcc/bin with names prefixed by "new-". You can use
- --program-transform-name if you have multiple versions of GCC, and
- wish to be sure about which version you are invoking.
-
- If you use --prefix, GCC may have difficulty locating a GNU assembler
- or linker on your system, [42]GCC can not find GNU as/GNU ld explains
- how to deal with this.
-
- Another option that may be easier is to use the --program-prefix= or
- --program-suffix= options to configure. So if you're installing GCC
- 2.95.2 and don't want to disturb the current version of GCC in
- /usr/local/bin/, you could do
-
- configure --program-suffix=-2.95.2 <other configure options>
-
- This should result in GCC being installed as /usr/local/bin/gcc-2.95.2
- instead of /usr/local/bin/gcc.
- _________________________________________________________________
-
-Dynamic linker is unable to find GCC libraries
-
- This problem manifests itself by programs not finding shared libraries
- they depend on when the programs are started. Note this problem often
- manifests itself with failures in the libio/libstdc++ tests after
- configuring with --enable-shared and building GCC.
-
- GCC does not specify a runpath so that the dynamic linker can find
- dynamic libraries at runtime.
-
- The short explanation is that if you always pass a -R option to the
- linker, then your programs become dependent on directories which may
- be NFS mounted, and programs may hang unnecessarily when an NFS server
- goes down.
-
- The problem is not programs that do require the directories; those
- programs are going to hang no matter what you do. The problem is
- programs that do not require the directories.
-
- SunOS effectively always passed a -R option for every -L option; this
- was a bad idea, and so it was removed for Solaris. We should not
- recreate it.
-
- However, if you feel you really need such an option to be passed
- automatically to the linker, you may add it to the GCC specs file.
- This file can be found in the same directory that contains cc1 (run
- gcc -print-prog-name=cc1 to find it). You may add linker flags such as
- -R or -rpath, depending on platform and linker, to the *link or *lib
- specs.
-
- Another alternative is to install a wrapper script around gcc, g++ or
- ld that adds the appropriate directory to the environment variable
- LD_RUN_PATH or equivalent (again, it's platform-dependent).
-
- Yet another option, that works on a few platforms, is to hard-code the
- full pathname of the library into its soname. This can only be
- accomplished by modifying the appropriate .ml file within
- libstdc++/config (and also libg++/config, if you are building libg++),
- so that $(libdir)/ appears just before the library name in -soname or
- -h options.
- _________________________________________________________________
-
-GCC can not find GNU as/GNU ld
-
- GCC searches the PATH for an assembler and a loader, but it only does
- so after searching a directory list hard-coded in the GCC executables.
- Since, on most platforms, the hard-coded list includes directories in
- which the system assembler and loader can be found, you may have to
- take one of the following actions to arrange that GCC uses the GNU
- versions of those programs.
-
- To ensure that GCC finds the GNU assembler (the GNU loader), which are
- required by [43]some configurations, you should configure these with
- the same --prefix option as you used for GCC. Then build & install GNU
- as (GNU ld) and proceed with building GCC.
-
- Another alternative is to create links to GNU as and ld in any of the
- directories printed by the command `gcc -print-search-dirs | grep
- '^programs:''. The link to `ld' should be named `real-ld' if `ld'
- already exists. If such links do not exist while you're compiling GCC,
- you may have to create them in the build directories too, within the
- gcc directory and in all the gcc/stage* subdirectories.
-
- GCC 2.95 allows you to specify the full pathname of the assembler and
- the linker to use. The configure flags are `--with-as=/path/to/as' and
- `--with-ld=/path/to/ld'. GCC will try to use these pathnames before
- looking for `as' or `(real-)ld' in the standard search dirs. If, at
- configure-time, the specified programs are found to be GNU utilities,
- `--with-gnu-as' and `--with-gnu-ld' need not be used; these flags will
- be auto-detected. One drawback of this option is that it won't allow
- you to override the search path for assembler and linker with
- command-line options -B/path/ if the specified filenames exist.
- _________________________________________________________________
-
-cpp: Usage:... Error
-
- If you get an error like this when building GCC (particularly when
- building __mulsi3), then you likely have a problem with your
- environment variables.
- cpp: Usage: /usr/lib/gcc-lib/i586-unknown-linux-gnulibc1/2.7.2.3/cpp
- [switches] input output
-
- First look for an explicit '.' in either LIBRARY_PATH or
- GCC_EXEC_PREFIX from your environment. If you do not find an explicit
- '.', look for an empty pathname in those variables. Note that ':' at
- either the start or end of these variables is an implicit '.' and will
- cause problems.
-
- Also note '::' in these paths will also cause similar problems.
- _________________________________________________________________
-
-Optimizing the compiler itself
-
- If you want to test a particular optimization option, it's useful to
- try bootstrapping the compiler with that option turned on. For
- example, to test the -fssa option, you could bootstrap like this:
-make BOOT_CFLAGS="-O2 -fssa" bootstrap
- _________________________________________________________________
-
- Testsuite problems
-
-Unable to run the testsuite
-
- If you get a message about unable to find "standard.exp" when trying
- to run the GCC testsuites, then your dejagnu is too old to run the GCC
- tests. You will need to get a newer version of dejagnu from
- [44]http://www.gnu.org/software/dejagnu/dejagnu.html.
- _________________________________________________________________
-
-How do I pass flags like -fnew-abi to the testsuite?
-
- If you invoke runtest directly, you can use the --tool_opts option,
- e.g:
- runtest --tool_opts "-fnew-abi -fno-honor-std" <other options>
-
- Or, if you use make check you can use the make variable RUNTESTFLAGS,
- e.g:
- make RUNTESTFLAGS="--tool_opts '-fnew-abi -fno-honor-std'" check-g++
- _________________________________________________________________
-
-How can I run the test suite with multiple options?
-
- If you invoke runtest directly, you can use the --target_board option,
- e.g:
- runtest --target_board "unix{-fPIC,-fpic,}" <other options>
-
- Or, if you use make check you can use the make variable RUNTESTFLAGS,
- e.g:
- make RUNTESTFLAGS="--target_board 'unix{-fPIC,-fpic,}'" check-gcc
-
- Either of these examples will run the tests three times. Once with
- -fPIC, once with -fpic, and once with no additional flags.
-
- This technique is particularly useful on multilibbed targets.
- _________________________________________________________________
-
- Older versions of GCC and EGCS
-
-Is there a stringstream / sstream for GCC 2.95.2?
-
- Yes, it's at:
- [45]http://gcc.gnu.org/ml/libstdc++/2000-q2/msg00700/sstream.
- _________________________________________________________________
-
- Miscellaneous
-
-Friend Templates
-
- In order to make a specialization of a template function a friend of a
- (possibly template) class, you must explicitly state that the friend
- function is a template, by appending angle brackets to its name, and
- this template function must have been declared already. Here's an
- example:
-template <typename T> class foo {
- friend void bar(foo<T>);
-}
-
- The above declaration declares a non-template function named bar, so
- it must be explicitly defined for each specialization of foo. A
- template definition of bar won't do, because it is unrelated with the
- non-template declaration above. So you'd have to end up writing:
-void bar(foo<int>) { /* ... */ }
-void bar(foo<void>) { /* ... */ }
-
- If you meant bar to be a template function, you should have
- forward-declared it as follows. Note that, since the template function
- declaration refers to the template class, the template class must be
- forward-declared too:
-template <typename T>
-class foo;
-
-template <typename T>
-void bar(foo<T>);
-
-template <typename T>
-class foo {
- friend void bar<>(foo<T>);
-};
-
-template <typename T>
-void bar(foo<T>) { /* ... */ }
-
- In this case, the template argument list could be left empty, because
- it can be implicitly deduced from the function arguments, but the
- angle brackets must be present, otherwise the declaration will be
- taken as a non-template function. Furthermore, in some cases, you may
- have to explicitly specify the template arguments, to remove
- ambiguity.
-
- An error in the last public comment draft of the ANSI/ISO C++ Standard
- and the fact that previous releases of GCC would accept such friend
- declarations as template declarations has led people to believe that
- the forward declaration was not necessary, but, according to the final
- version of the Standard, it is.
- _________________________________________________________________
-
-dynamic_cast, throw, typeid don't work with shared libraries
-
- The new C++ ABI in the GCC 3.0 series uses address comparisons, rather
- than string compares, to determine type equality. This leads to better
- performance. Like other objects that have to be present in the final
- executable, these std::typeinfo_t objects have what is called vague
- linkage because they are not tightly bound to any one particular
- translation unit (object file). The compiler has to emit them in any
- translation unit that requires their presence, and then rely on the
- linking and loading process to make sure that only one of them is
- active in the final executable. With static linking all of these
- symbols are resolved at link time, but with dynamic linking, further
- resolution occurs at load time. You have to ensure that objects within
- a shared library are resolved against objects in the executable and
- other shared libraries.
- * For a program which is linked against a shared library, no
- additional precautions need taking.
- * You cannot create a shared library with the "-Bsymbolic" option,
- as that prevents the resolution described above.
- * If you use dlopen to explicitly load code from a shared library,
- you must do several things. First, export global symbols from the
- executable by linking it with the "-E" flag (you will have to
- specify this as "-Wl,-E" if you are invoking the linker in the
- usual manner from the compiler driver, g++). You must also make
- the external symbols in the loaded library available for
- subsequent libraries by providing the RTLD_GLOBAL flag to dlopen.
- The symbol resolution can be immediate or lazy.
-
- Template instantiations are another, user visible, case of objects
- with vague linkage, which needs similar resolution. If you do not take
- the above precautions, you may discover that a template instantiation
- with the same argument list, but instantiated in multiple translation
- units, has several addresses, depending in which translation unit the
- address is taken. (This is not an exhaustive list of the kind of
- objects which have vague linkage and are expected to be resolved
- during linking & loading.)
-
- If you are worried about different objects with the same name
- colliding during the linking or loading process, then you should use
- namespaces to disambiguate them. Giving distinct objects with global
- linkage the same name is a violation of the One Definition Rule (ODR)
- [basic.def.odr].
-
- For more details about the way that GCC implements these and other C++
- features, please read the [46]ABI specification. Note the
- std::typeinfo_t objects which must be resolved all begin with "_ZTS".
- Refer to ld's documentation for a description of the "-E" &
- "-Bsymbolic" flags.
- _________________________________________________________________
-
-Why do I need autoconf, bison, xgettext, automake, etc?
-
- If you're using diffs up dated from one snapshot to the next, or if
- you're using the CVS repository, you may need several additional
- programs to build GCC.
-
- These include, but are not necessarily limited to autoconf, automake,
- bison, and xgettext.
-
- This is necessary because neither diff nor cvs keep timestamps
- correct. This causes problems for generated files as "make" may think
- those generated files are out of date and try to regenerate them.
-
- An easy way to work around this problem is to use the gcc_update
- script in the contrib subdirectory of GCC, which handles this
- transparently without requiring installation of any additional tools.
- (Note: Up to and including GCC 2.95 this script was called egcs_update
- .)
-
- When building from diffs or CVS or if you modified some sources, you
- may also need to obtain development versions of some GNU tools, as the
- production versions do not necessarily handle all features needed to
- rebuild GCC.
-
- In general, the current versions of these tools from
- [47]ftp://ftp.gnu.org/gnu/ will work. At present, Autoconf 2.50 is not
- supported, and you will need to use Autoconf 2.13; work is in progress
- to fix this problem. Also look at
- [48]ftp://gcc.gnu.org/pub/gcc/infrastructure/ for any special versions
- of packages.
- _________________________________________________________________
-
-Why can't I build a shared library?
-
- When building a shared library you may get an error message from the
- linker like `assert pure-text failed:' or `DP relative code in file'.
-
- This kind of error occurs when you've failed to provide proper flags
- to gcc when linking the shared library.
-
- You can get this error even if all the .o files for the shared library
- were compiled with the proper PIC option. When building a shared
- library, gcc will compile additional code to be included in the
- library. That additional code must also be compiled with the proper
- PIC option.
-
- Adding the proper PIC option (-fpic or -fPIC) to the link line which
- creates the shared library will fix this problem on targets that
- support PIC in this manner. For example:
- gcc -c -fPIC myfile.c
- gcc -shared -o libmyfile.so -fPIC myfile.o
- _________________________________________________________________
-
-When building C++, the linker says my constructors, destructors or virtual
-tables are undefined, but I defined them
-
- The ISO C++ Standard specifies that all virtual methods of a class
- that are not pure-virtual must be defined, but does not require any
- diagnostic for violations of this rule [class.virtual]/8. Based on
- this assumption, GCC will only emit the implicitly defined
- constructors, the assignment operator, the destructor and the virtual
- table of a class in the translation unit that defines its first such
- non-inline method.
-
- Therefore, if you fail to define this particular method, the linker
- may complain about the lack of definitions for apparently unrelated
- symbols. Unfortunately, in order to improve this error message, it
- might be necessary to change the linker, and this can't always be
- done.
-
- The solution is to ensure that all virtual methods that are not pure
- are defined. Note that a destructor must be defined even if it is
- declared pure-virtual [class.dtor]/7.
- _________________________________________________________________
-
-Will GCC someday include an incremental linker?
-
- Incremental linking is part of the linker, not the compiler. As such,
- GCC doesn't have anything to do with incremental linking. Depending on
- what platform you use, it may be possible to tell GCC to use the
- platform's native linker (e.g., Solaris' ild(1)).
-
-References
-
- 1. http://gcc.gnu.org/faq.html
- 2. http://www.eskimo.com/~scs/C-faq/top.html
- 3. http://www.jamesd.demon.co.uk/csc/faq.html
- 4. http://www.fortran.com/fortran/info.html
- 5. http://gcc.gnu.org/onlinedocs/libstdc++/faq/index.html
- 6. http://gcc.gnu.org/java/faq.html
- 7. http://gcc.gnu.org/faq.html#general
- 8. http://gcc.gnu.org/faq.html#gcc
- 9. http://gcc.gnu.org/faq.html#cygnus
- 10. http://gcc.gnu.org/faq.html#open-development
- 11. http://gcc.gnu.org/faq.html#bugreport
- 12. http://gcc.gnu.org/faq.html#support
- 13. http://gcc.gnu.org/faq.html#platforms
- 14. http://gcc.gnu.org/faq.html#installation
- 15. http://gcc.gnu.org/faq.html#multiple
- 16. http://gcc.gnu.org/faq.html#rpath
- 17. http://gcc.gnu.org/faq.html#rpath
- 18. http://gcc.gnu.org/faq.html#gas
- 19. http://gcc.gnu.org/faq.html#environ
- 20. http://gcc.gnu.org/faq.html#optimizing
- 21. http://gcc.gnu.org/faq.html#testsuite
- 22. http://gcc.gnu.org/faq.html#dejagnu
- 23. http://gcc.gnu.org/faq.html#testoptions
- 24. http://gcc.gnu.org/faq.html#multipletests
- 25. http://gcc.gnu.org/faq.html#old
- 26. http://gcc.gnu.org/faq.html#2.95sstream
- 27. http://gcc.gnu.org/faq.html#misc
- 28. http://gcc.gnu.org/faq.html#friend
- 29. http://gcc.gnu.org/faq.html#dso
- 30. http://gcc.gnu.org/faq.html#generated_files
- 31. http://gcc.gnu.org/faq.html#picflag-needed
- 32. http://gcc.gnu.org/faq.html#vtables
- 33. http://gcc.gnu.org/faq.html#incremental
- 34. http://gcc.gnu.org/steering.html
- 35. http://gcc.gnu.org/steering.html
- 36. http://gcc.gnu.org/faq.html#cathedral-vs-bazaar
- 37. http://gcc.gnu.org/bugs.html
- 38. http://gcc.gnu.org/bugs.html
- 39. http://gcc.gnu.org/bugs.html
- 40. http://gcc.gnu.org/install/specific.html
- 41. http://gcc.gnu.org/buildstat.html
- 42. http://gcc.gnu.org/faq.html#gas
- 43. http://gcc.gnu.org/install/specific.html
- 44. http://www.gnu.org/software/dejagnu/dejagnu.html
- 45. http://gcc.gnu.org/ml/libstdc++/2000-q2/msg00700/sstream
- 46. http://www.codesourcery.com/cxx-abi/
- 47. ftp://ftp.gnu.org/gnu/
- 48. ftp://gcc.gnu.org/pub/gcc/infrastructure/
projects / msp430-gcc.git / blobdiff