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 <div class="doc_title">
   Bootstrapping the C/C++ Front-End
 </div>

 <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
 <ul>
   <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>
 </ul>

 <p>We welcome patches to help make this process simpler.</p>

 <!-- *********************************************************************** -->
 <div class="doc_section">
   <a name="instructions">Instructions</a>
 </div>
 <!-- *********************************************************************** -->

 <div class="doc_text">
 <p>
 <ol>
 <li><p>Configure and build the LLVM libraries and tools using:</p>
 <pre>
  % cd llvm
  % ./configure [options...]
  % gmake tools-only
 </pre>
     <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>
 <pre>
  % set path = ( `cd llvm/tools/Debug &amp;&amp; pwd` $path )
 </pre></li>

 <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"
        tree.</p>
 <pre>
  % pwd
  /usr/local/example/cfrontend/src
  % cd ..
  % mkdir build install
  % set CFEINSTALL = `pwd`/install
 </pre></li>

 <li><p>Configure, build and install the C front-end:</p>
 <pre>
  % cd build
  % ../src/configure --prefix=$CFEINSTALL --disable-nls --disable-shared \
    --enable-languages=c,c++
  % gmake all-gcc
  % setenv LLVM_LIB_SEARCH_PATH `pwd`/gcc
  % gmake all; gmake install
 </pre>

  <p><b>Common Problem:</b> You may get error messages regarding the fact
  that LLVM does not support inline assembly. Here are two common
  fixes:</p>

  <ul>
   <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
    <code>$CFEINSTALL/<i>target-triplet</i>/sys-include</code>.</p></li>

   <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
    <code>src/libstdc++-v3/config/cpu/<i>name-of-cpu</i>/atomicity.h</code>
    and apply a patch so that it does not use inline assembly.</p></li>
  </ul>

  <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>

  <ul>
   <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
       headers.</li>
  </ul>
 </li>

 <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>$CFEINSTALL/<i>target-triplet</i>/sys-include</code> to
 <code>$CFEINSTALL/lib/gcc/<i>target-triplet</i>/3.4-llvm/include</code>.
 (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>
 <pre>
  % gmake -C runtime
  % mkdir $CFEINSTALL/bytecode-libs
  % gmake -C runtime install
  % setenv LLVM_LIB_SEARCH_PATH $CFEINSTALL/bytecode-libs
 </pre></li>

 <li><p>Test the newly-installed C frontend by one or more of the
 following means:</p>
  <ul>
   <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
    test/Programs</code></li>
  </ul>
   </p>
 </li>
 </ol>
 </div>

 <!-- *********************************************************************** -->

 <hr><font size="-1">
 <address><a href="mailto:gaeke -at- uiuc.edu">Brian Gaeke</a></address>
 <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
 <br>
 Last modified: $Date$
 </font>

 </body>
 </html>
	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
	<html>
	<head>
	<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
	<link rel="stylesheet" href="llvm.css" type="text/css" media="screen" />
	<title>Bootstrapping the C/C++ Front-End</title>
	</head>
	<body>

	<div class="doc_title">
	Bootstrapping the C/C++ Front-End
	</div>

	<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
	<ul>
	<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>
	</ul>

	<p>We welcome patches to help make this process simpler.</p>

	<!-- *********************************************************************** -->
	<div class="doc_section">
	<a name="instructions">Instructions</a>
	</div>
	<!-- *********************************************************************** -->

	<div class="doc_text">
	<p>
	<ol>
	<li><p>Configure and build the LLVM libraries and tools using:</p>
	<pre>
	% cd llvm
	% ./configure [options...]
	% gmake tools-only
	</pre>
	<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>
	<pre>
	% set path = ( `cd llvm/tools/Debug && pwd` $path )
	</pre></li>

	<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"
	tree.</p>
	<pre>
	% pwd
	/usr/local/example/cfrontend/src
	% cd ..
	% mkdir build install
	% set CFEINSTALL = `pwd`/install
	</pre></li>

	<li><p>Configure, build and install the C front-end:</p>
	<pre>
	% cd build
	% ../src/configure --prefix=$CFEINSTALL --disable-nls --disable-shared \
	--enable-languages=c,c++
	% gmake all-gcc
	% setenv LLVM_LIB_SEARCH_PATH `pwd`/gcc
	% gmake all; gmake install
	</pre>

	<p><b>Common Problem:</b> You may get error messages regarding the fact
	that LLVM does not support inline assembly. Here are two common
	fixes:</p>

	<ul>
	<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
	<code>$CFEINSTALL/<i>target-triplet</i>/sys-include</code>.</p></li>

	<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
	<code>src/libstdc++-v3/config/cpu/<i>name-of-cpu</i>/atomicity.h</code>
	and apply a patch so that it does not use inline assembly.</p></li>
	</ul>

	<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>

	<ul>
	<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
	headers.</li>
	</ul>
	</li>

	<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>$CFEINSTALL/<i>target-triplet</i>/sys-include</code> to
	<code>$CFEINSTALL/lib/gcc/<i>target-triplet</i>/3.4-llvm/include</code>.
	(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>
	<pre>
	% gmake -C runtime
	% mkdir $CFEINSTALL/bytecode-libs
	% gmake -C runtime install
	% setenv LLVM_LIB_SEARCH_PATH $CFEINSTALL/bytecode-libs
	</pre></li>

	<li><p>Test the newly-installed C frontend by one or more of the
	following means:</p>
	<ul>
	<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
	test/Programs</code></li>
	</ul>
	</p>
	</li>
	</ol>
	</div>

	<!-- *********************************************************************** -->

	<hr><font size="-1">
	<address><a href="mailto:gaeke -at- uiuc.edu">Brian Gaeke</a></address>
	<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
	<br>
	Last modified: $Date$
	</font>

	</body>
	</html>