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