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<title>Bootstrapping the C/C++ Front-End</title>
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<div class="doc_title">
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Bootstrapping the C/C++ Front-End
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</div>
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<p>This document is intended to explain the process of building the LLVM
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C/C++ front-end, based on GCC 3.4, from source.</p>
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<p><b>NOTE:</b> This is currently a somewhat fragile, error-prone
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process, and you should only try to do it if (A) you really, really,
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really can't use the binaries we distribute, and (B) you are a wicked
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good GCC hacker.</p>
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<p>We welcome patches to help make this process simpler.</p>
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<!-- *********************************************************************** -->
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<div class="doc_section">
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<a name="instructions">Instructions</a>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>
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<ol>
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<li><p>Configure and build the LLVM libraries and tools using:</p>
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<pre>
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% cd llvm
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% ./configure [options...]
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% gmake tools-only
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</pre>
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<p>The use of the non-default target "tools-only" means that the
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LLVM tools and libraries will build, and the binaries will be
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deposited in llvm/tools/Debug, but the runtime (bytecode)
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libraries will not build.</p></li>
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<li><p>Add the directory containing the tools to your PATH.</p>
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<pre>
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% set path = ( `cd llvm/tools/Debug && pwd` $path )
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</pre></li>
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<li><p>Unpack the C/C++ front-end source into cfrontend/src.</p></li>
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<li><p>Edit src/configure. Change the first line (starting w/ #!) to
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contain the correct full pathname of sh.</p></li>
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<li><p>Make "build" and "install" directories as siblings of the "src"
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tree.</p>
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<pre>
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% pwd
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/usr/local/example/cfrontend/src
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% cd ..
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% mkdir build install
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% set CFEINSTALL = `pwd`/install
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</pre></li>
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<li><p>Configure, build and install the C front-end:</p>
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<pre>
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% cd build
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% ../src/configure --prefix=$CFEINSTALL --disable-nls --disable-shared \
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--enable-languages=c,c++
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% gmake all-gcc
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% setenv LLVM_LIB_SEARCH_PATH `pwd`/gcc
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% gmake all; gmake install
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</pre>
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<p><b>Common Problem:</b> You may get error messages regarding the fact
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that LLVM does not support inline assembly. Here are two common
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fixes:</p>
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<ul>
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<li><p><b>Fix 1:</b> If you have system header files that include
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inline assembly, you may have to modify them to remove the inline
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assembly, and install the modified versions in
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<code>$CFEINSTALL/<i>target-triplet</i>/sys-include</code>.</p></li>
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<li><b>Fix 2:</b> If you are building the C++ front-end on a CPU we
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haven't tried yet, you will probably have to edit the appropriate
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version of atomicity.h under
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<code>src/libstdc++-v3/config/cpu/<i>name-of-cpu</i>/atomicity.h</code>
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and apply a patch so that it does not use inline assembly.</p></li>
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</ul>
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<p><b>Porting to a new architecture:</b> If you are porting the new front-end
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to a new architecture, or compiling in a different configuration that we have
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previously, there are probably several changes you will have to make to the GCC
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target to get it to work correctly. These include:<p>
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<ul>
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<li>Often targets include special or assembler linker flags which
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<tt>gccas</tt>/<tt>gccld</tt> does not understand. In general, these can
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just be removed.</li>
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<li>LLVM currently does not support any floating point values other than
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32-bit and 64-bit IEEE floating point. The primary effect of this is
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that you may have to map "long double" onto "double".</li>
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<li>The profiling hooks in GCC do not apply at all to the LLVM front-end.
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These may need to be disabled.</li>
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<li>No inline assembly for position independent code. At the LLVM level,
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everything is position independent.</li>
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<li>We handle <tt>.init</tt> and <tt>.fini</tt> differently.</li>
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<li>You may have to disable multilib support in your target. Using multilib
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support causes the GCC compiler driver to add a lot of "<tt>-L</tt>"
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options to the link line, which do not relate to LLVM and confuse
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<tt>gccld</tt>. To disable multilibs, delete any
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<tt>MULTILIB_OPTIONS</tt> lines from your target files.</li>
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<li>Did we mention that we don't support inline assembly? You'll probably
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have to add some fixinclude hacks to disable it in the system
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headers.</li>
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</ul>
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</li>
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<li><p>Go back into the LLVM source tree proper. Edit Makefile.config
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to redefine <code>LLVMGCCDIR</code> to the full pathname of the
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<code>$CFEINSTALL</code> directory, which is the directory you just
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installed the C front-end into. (The ./configure script is likely to
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have set this to a directory which does not exist on your system.)</p></li>
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<li><p>If you edited header files during the C/C++ front-end build as
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described in "Fix 1" above, you must now copy those header files from
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<code>$CFEINSTALL/<i>target-triplet</i>/sys-include</code> to
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<code>$CFEINSTALL/lib/gcc/<i>target-triplet</i>/3.4-llvm/include</code>.
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(This should be the "include" directory in the same directory as the
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libgcc.a library, which you can find by running
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<code>$CFEINSTALL/bin/gcc --print-libgcc-file-name</code>.)</p></li>
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<li><p>Build and install the runtime (bytecode) libraries by running:</p>
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<pre>
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% gmake -C runtime
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% mkdir $CFEINSTALL/bytecode-libs
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% gmake -C runtime install
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% setenv LLVM_LIB_SEARCH_PATH $CFEINSTALL/bytecode-libs
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</pre></li>
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<li><p>Test the newly-installed C frontend by one or more of the
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following means:</p>
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<ul>
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<li> compiling and running a "hello, LLVM" program in C and C++.</li>
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<li> running the tests under <tt>test/Programs</tt> using <code>gmake -C
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test/Programs</code></li>
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</ul>
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</p>
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</li>
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</ol>
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</div>
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<!-- *********************************************************************** -->
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<hr><font size="-1">
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<address><a href="mailto:gaeke -at- uiuc.edu">Brian Gaeke</a></address>
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Last modified: $Date$
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</font>
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</body>
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</html>
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