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diff --git a/gcc-4.2.1/faq.html b/gcc-4.2.1/faq.html new file mode 100644 index 000000000..61b0e9a4f --- /dev/null +++ b/gcc-4.2.1/faq.html @@ -0,0 +1,598 @@ +<html> + +<head> +<title>GCC Frequently Asked Questions</title> +</head> + +<body> + +<h1>GCC Frequently Asked Questions</h1> + +<p>The latest version of this document is always available at +<a href="http://gcc.gnu.org/faq.html">http://gcc.gnu.org/faq.html</a>.</p> + +<p>This FAQ tries to answer specific questions concerning GCC. For +general information regarding C, C++, resp. Fortran please check the +<a href="http://c-faq.com/">comp.lang.c FAQ</a>, +<a href="http://www.comeaucomputing.com/csc/faq.html">comp.std.c++ +FAQ</a>, +and the <a href="http://www.fortran.com/fortran/info.html">Fortran +Information page</a>.</p> + +<p>Other GCC-related FAQs: + <a href="http://gcc.gnu.org/onlinedocs/libstdc++/faq/index.html"> + libstdc++-v3</a>, and + <a href="http://gcc.gnu.org/java/faq.html">GCJ</a>.</p> + +<hr /> +<h1>Questions</h1> +<ol> + <li><a href="#general">General information</a> + <ol> + <li><a href="#open-development">What is an open development model?</a></li> + <li><a href="#support">How do I get a bug fixed or a feature added?</a></li> + <li><a href="#platforms">Does GCC work on my platform?</a></li> + </ol></li> + + <li><a href="#installation">Installation</a> + <ol> + <li><a href="#multiple">How to install multiple versions of GCC</a></li> + <li><a href="#rpath">Dynamic linker is unable to find GCC libraries</a></li> + <li><a href="#rpath">libstdc++/libio tests fail badly with --enable-shared</a></li> + <li><a href="#gas">GCC can not find GNU as/GNU ld</a></li> + <li><a href="#environ">cpp: Usage:... Error</a></li> + <li><a href="#optimizing">Optimizing the compiler itself</a></li> + <li><a href="#iconv">Why does <code>libiconv</code> get linked into <code>jc1</code> on Solaris?</a></li> + </ol></li> + + <li><a href="#testsuite">Testsuite problems</a> + <ol> + <li><a href="#testoptions">How do I pass flags like + <code>-fnew-abi</code> to the testsuite?</a></li> + <li><a href="#multipletests">How can I run the test suite with multiple options?</a></li> + </ol></li> + + <li><a href="#misc">Miscellaneous</a> + <ol> + <li><a href="#friend">Friend Templates</a></li> + <li><a href="#dso"><code>dynamic_cast</code>, <code>throw</code>, <code>typeid</code> don't work with shared libraries</a></li> + <li><a href="#generated_files">Why do I need autoconf, bison, xgettext, automake, etc?</a></li> + <li><a href="#picflag-needed">Why can't I build a shared library?</a></li> + <li><a href="#vtables">When building C++, the linker says my constructors, destructors or virtual tables are undefined, but I defined them</a></li> + <li><a href="#incremental">Will GCC someday include an incremental linker?</a></li> + </ol></li> +</ol> + + +<hr /> +<a name="general"></a> +<h1>General information</h1> + +<h2><a name="open-development">What is an open development model?</a></h2> + +<p>We are using a bazaar style +<a href="#cathedral-vs-bazaar"><b>[1]</b></a> +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.</p> + +<p>In addition to weekly snapshots of the GCC development sources, we +have the sources readable from an SVN server by anyone. Furthermore we +are using SVN to allow maintainers write access to the sources.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + +<blockquote> +<a name="cathedral-vs-bazaar"><b>[1]</b></a> + 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 <b>cathedral</b> development model versus a <b>bazaar</b> + 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. +</blockquote> + +<hr /> +<!-- The "bugreport" anchor was used in ICE messages of GCC < 2.95.3. --> +<h2 id="bugreport"><a name="support">How do I get a bug fixed or + a feature added?</a></h2> + +<p>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 decreasing 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.</p> + +<ul> +<li>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.</li> + +<li><a href="bugs.html">Report the problem to the GCC bug tracking system</a> + 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.</li> + +<li>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.</li> +</ul> + +<hr /> +<h2><a name="platforms">Does GCC work on my platform?</a></h2> + +<p>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 <a href="http://gcc.gnu.org/install/specific.html">latest version</a> +is always available at the GCC web site. +Reports of <a href="http://gcc.gnu.org/buildstat.html">successful builds</a> +for several versions of GCC are also available at the web site.</p> + +<hr /> +<a name="installation"></a> +<h1>Installation</h1> + +<h2><a name="multiple">How to install multiple versions of GCC</a></h2> + +<p>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.</p> + +<p>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.</p> + +<p>The easiest way to do this is to configure the new GCC with +<code>--prefix=/usr/local/gcc</code> and the older gcc2 with +<code>--prefix=/usr/local/gcc2</code>. Build and install both +compilers. Then make a symlink from <code>/usr/local/bin/gcc</code> +to <code>/usr/local/gcc/bin/gcc</code> and from +<code>/usr/local/bin/gcc2</code> to +<code>/usr/local/gcc2/bin/gcc</code>. Create similar links for the +"g++", "c++" and "g77" compiler drivers.</p> + +<p>An alternative to using symlinks is to configure with a +<code>--program-transform-name</code> 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 +<code>--prefix</code> 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 <code>--program-transform-name</code> 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:</p> +<blockquote><code> +--program-transform-name='s,\\\\(.*\\\\),new-\\\\1,' +</code></blockquote> +<p>With the above <code>--prefix</code> option, that will install the new +GCC programs into <code>/usr/local/gcc/bin</code> with names prefixed +by "new-". You can use <code>--program-transform-name</code> if you +have multiple versions of GCC, and wish to be sure about which version +you are invoking.</p> + +<p>If you use <code>--prefix</code>, GCC may have difficulty locating a GNU +assembler or linker on your system, <a href="#gas">GCC can not find GNU +as/GNU ld</a> explains how to deal with this.</p> + +<p>Another option that may be easier is to use the +<code>--program-prefix=</code> or <code>--program-suffix=</code> +options to configure. So if you're installing GCC 2.95.2 and don't +want to disturb the current version of GCC in +<code>/usr/local/bin/</code>, you could do</p> +<blockquote><code> +configure --program-suffix=-2.95.2 <other configure options> +</code></blockquote> +<p>This should result in GCC being installed as +<code>/usr/local/bin/gcc-2.95.2</code> instead of +<code>/usr/local/bin/gcc</code>.</p> + +<hr /> +<h2><a name="rpath">Dynamic linker is unable to find GCC libraries</a></h2> + +<p>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 <code>--enable-shared</code> and building GCC.</p> + +<p>GCC does not specify a runpath so that the dynamic linker can find +dynamic libraries at runtime.</p> + +<p>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.</p> + +<p>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.</p> + +<p>SunOS effectively always passed a <code>-R</code> option for every +<code>-L</code> option; this was a bad idea, and so it was removed for +Solaris. We should not recreate it.</p> + +<p>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 +<code>gcc -print-prog-name=cc1</code> to find it). You may add linker +flags such as <code>-R</code> or <code>-rpath</code>, depending on +platform and linker, to the <code>*link</code> or <code>*lib</code> +specs.</p> + +<p>Another alternative is to install a wrapper script around gcc, g++ +or ld that adds the appropriate directory to the environment variable +<code>LD_RUN_PATH</code> or equivalent (again, it's +platform-dependent).</p> + +<p>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 <tt>.ml</tt> file within +<tt>libstdc++/config</tt> (and also <tt>libg++/config</tt>, if you are +building libg++), so that <code>$(libdir)/</code> appears just before +the library name in <code>-soname</code> or <code>-h</code> options.</p> + +<hr /> +<h2><a name="gas">GCC can not find GNU as/GNU ld</a></h2> +<p>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.</p> + +<p>To ensure that GCC finds the GNU assembler (the GNU loader), which +are required by <a href="http://gcc.gnu.org/install/specific.html">some +configurations</a>, +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.</p> + +<p>Another alternative is to create links to GNU as and ld in any of +the directories printed by the command `<tt>gcc -print-search-dirs | +grep '^programs:'</tt>'. The link to `<tt>ld</tt>' should be named +`<tt>real-ld</tt>' if `<tt>ld</tt>' 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 <tt>gcc</tt> directory +<em>and</em> in all the <tt>gcc/stage*</tt> subdirectories.</p> + +<p>GCC 2.95 allows you to specify the full pathname of the assembler +and the linker to use. The configure flags are +`<tt>--with-as=/path/to/as</tt>' and `<tt>--with-ld=/path/to/ld</tt>'. +GCC will try to use these pathnames before looking for `<tt>as</tt>' +or `<tt>(real-)ld</tt>' in the standard search dirs. If, at +configure-time, the specified programs are found to be GNU utilities, +`<tt>--with-gnu-as</tt>' and `<tt>--with-gnu-ld</tt>' 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 <tt>-B/path/</tt> if the +specified filenames exist.</p> + +<hr /> +<h2><a name="environ">cpp: Usage:... Error</a></h2> + +<p>If you get an error like this when building GCC (particularly when building +__mulsi3), then you likely have a problem with your environment variables.</p> +<pre> + cpp: Usage: /usr/lib/gcc-lib/i586-unknown-linux-gnulibc1/2.7.2.3/cpp + [switches] input output +</pre> +<p>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.</p> + +<p>Also note '::' in these paths will also cause similar problems.</p> + + +<hr /> +<h2><a name="optimizing">Optimizing the compiler itself</a></h2> + +<p>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 <code>-fssa</code> option, you could bootstrap like this:</p> + +<pre>make BOOT_CFLAGS="-O2 -fssa" bootstrap</pre> + +<hr /> +<h2><a name="iconv">Why does <code>libiconv</code> get linked into <code>jc1</code> on Solaris?</a></h2> + +<p>The Java front end requires <code>iconv</code>. If the compiler +used to bootstrap GCC finds <code>libiconv</code> (because the GNU +version of <code>libiconv</code> has been installed in the same prefix +as the bootstrap compiler), but the newly built GCC does not find the +library (because it will be installed with a different prefix), then a +link-time error will occur when building <code>jc1</code>. This +problem does not show up so often on platforms that have +<code>libiconv</code> in a default location (like +<code>/usr/lib</code>) because then both compilers can find a library +named <code>libiconv</code>, even though it is a different +library.</p> + +<p>Using <code>--disable-nls</code> at configure-time does not +prevent this problem because <code>jc1</code> uses +<code>iconv</code> even in that case. Solutions include temporarily +removing the GNU <code>libiconv</code>, copying it to a default +location such as <code>/usr/lib/</code>, and using +<code>--enable-languages</code> at configure-time to disable Java.</p> + +<hr /> +<a name="testsuite"></a> +<h1>Testsuite problems</h1> + +<h2><a name="testoptions">How do I pass flags like + <code>-fnew-abi</code> to the testsuite?</a></h2> + +<p>If you invoke <code>runtest</code> directly, you can use the +<code>--tool_opts</code> option, e.g:</p> +<pre> + runtest --tool_opts "-fnew-abi -fno-honor-std" <other options> +</pre> +<p>Or, if you use <code>make check</code> you can use the +<code>make</code> variable <code>RUNTESTFLAGS</code>, e.g:</p> +<pre> + make RUNTESTFLAGS="--tool_opts '-fnew-abi -fno-honor-std'" check-g++ +</pre> + +<hr /> +<h2><a name="multipletests"> How can I run the test suite with multiple options? </a></h2> + +<p>If you invoke <code>runtest</code> directly, you can use the +<code>--target_board</code> option, e.g:</p> +<pre> + runtest --target_board "unix{-fPIC,-fpic,}" <other options> +</pre> +<p>Or, if you use <code>make check</code> you can use the +<code>make</code> variable <code>RUNTESTFLAGS</code>, e.g:</p> +<pre> + make RUNTESTFLAGS="--target_board 'unix{-fPIC,-fpic,}'" check-gcc +</pre> +<p>Either of these examples will run the tests three times. Once +with <code>-fPIC</code>, once with <code>-fpic</code>, and once with +no additional flags.</p> + +<p>This technique is particularly useful on multilibbed targets.</p> + + +<hr /> +<a name="misc"></a> +<h1>Miscellaneous</h1> + + +<h2><a name="friend">Friend Templates</a></h2> + +<p>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:</p> +<pre> +template <typename T> class foo { + friend void bar(foo<T>); +} +</pre> +<p>The above declaration declares a non-template function named +<code>bar</code>, so it must be explicitly defined for <b>each</b> +specialization of <code>foo</code>. A template definition of <code>bar</code> +won't do, because it is unrelated with the non-template declaration +above. So you'd have to end up writing:</p> +<pre> +void bar(foo<int>) { /* ... */ } +void bar(foo<void>) { /* ... */ } +</pre> +<p>If you meant <code>bar</code> 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:</p> +<pre> +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>) { /* ... */ } +</pre> +<p>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.</p> + +<p>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.</p> + + +<hr /> +<h2><a name="dso"><code>dynamic_cast</code>, <code>throw</code>, <code>typeid</code> don't work with shared libraries</a></h2> + +<p>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 <code>std::type_info</code> 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.</p> + +<ul> +<li>For a program which is linked against a shared library, no additional +precautions are needed.</li> + +<li>You cannot create a shared library with the "<code>-Bsymbolic</code>" +option, as that prevents the resolution described above.</li> + +<li>If you use <code>dlopen</code> 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 "<code>-E</code>" flag (you will +have to specify this as "<code>-Wl,-E</code>" if you are invoking +the linker in the usual manner from the compiler driver, <code>g++</code>). +You must also make the external symbols in the loaded library +available for subsequent libraries by providing the <code>RTLD_GLOBAL</code> +flag to <code>dlopen</code>. The symbol resolution can be immediate or +lazy.</li> + +</ul> + +<p>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 <em>not</em> an exhaustive list of the kind +of objects which have vague linkage and are expected to be resolved +during linking & loading.)</p> + +<p>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].</p> + +<p>For more details about the way that GCC implements these and other +C++ features, please read the <a +href="http://www.codesourcery.com/cxx-abi/">ABI specification</a>. +Note the <code>std::type_info</code> objects which <i>must</i> be +resolved all begin with "_ZTS". Refer to <code>ld</code>'s +documentation for a description of the "<code>-E</code>" & +"<code>-Bsymbolic</code>" flags.</p> + +<hr /> +<h2><a name="generated_files">Why do I need autoconf, bison, xgettext, automake, etc?</a></h2> + +<p>If you're using diffs up dated from one snapshot to the next, or +if you're using the SVN repository, you may need several additional programs +to build GCC.</p> + +<p>These include, but are not necessarily limited to autoconf, automake, +bison, and xgettext.</p> + +<p>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.</p> + +<p>An easy way to work around this problem is to use the <code>gcc_update +</code> script in the contrib subdirectory of GCC, which handles this +transparently without requiring installation of any additional tools.</p> + + +<p>When building from diffs or SVN 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.</p> + +<p>In general, the current versions of these tools from <a +href="ftp://ftp.gnu.org/gnu/">ftp://ftp.gnu.org/gnu/</a> 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 +<a href="ftp://gcc.gnu.org/pub/gcc/infrastructure/"> +ftp://gcc.gnu.org/pub/gcc/infrastructure/</a> for any special versions +of packages.</p> + + +<hr /> +<h2><a name="picflag-needed">Why can't I build a shared library?</a></h2> + +<p>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'.</p> + +<p>This kind of error occurs when you've failed to provide proper flags +to gcc when linking the shared library. </p> + +<p>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.</p> + +<p>Adding the proper PIC option (<tt>-fpic</tt> or <tt>-fPIC</tt>) to the link +line which creates the shared library will fix this problem on targets that +support PIC in this manner. For example:</p> +<pre> + gcc -c -fPIC myfile.c + gcc -shared -o libmyfile.so -fPIC myfile.o +</pre> + + +<hr /> +<h2><a name="vtables">When building C++, the linker says my constructors, destructors or virtual tables are undefined, but I defined them</a></h2> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + + +<hr /> +<h2><a name="incremental">Will GCC someday include an incremental linker?</a></h2> + +<p>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)).</p> + + +</body> +</html> |