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6 <title>Bootstrapping the LLVM C/C++ Front-End</title>
10 <div class="doc_title">
11 Bootstrapping the LLVM C/C++ Front-End
15 <li><a href="#cautionarynote">A Cautionary Note</a>
16 <li><a href="#instructions">Instructions</a>
19 <div class="doc_text">
20 <p><b>Written by Brian R. Gaeke</b></p>
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24 <div class="doc_section">
25 <a name="cautionarynote">A Cautionary Note</a>
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29 <div class="doc_text">
30 <p>This document is intended to explain the process of building the
31 LLVM C/C++ front-end, based on GCC 3.4, from its source code. You
32 would have to do this, for example, if you are porting LLVM to a new
33 architecture or operating system.</p>
35 <p><b>NOTE:</b> This is currently a somewhat fragile, error-prone
36 process, and you should <b>only</b> try to do it if:</p>
39 <li>you really, really, really can't use the binaries we distribute</li>
40 <li>you need GCC to fix some of the header files on your system</li>
41 <li>you are an elite GCC hacker.</li>
44 <p>We welcome patches to help make this process simpler.</p>
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48 <div class="doc_section">
49 <a name="instructions">Instructions</a>
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53 <div class="doc_text">
56 <li><p>Configure and build the LLVM libraries and tools using:</p>
59 % ./configure [options...]
62 <p>The use of the non-default target "tools-only" means that the
63 LLVM tools and libraries will build, and the binaries will be
64 deposited in llvm/tools/Debug, but the runtime (bytecode)
65 libraries will not build.</p></li>
67 <li><p>Add the directory containing the tools to your PATH.</p>
69 % set path = ( `cd llvm/tools/Debug && pwd` $path )
72 <li><p>Unpack the C/C++ front-end source into cfrontend/src.</p></li>
74 <li><p>Edit src/configure. Change the first line (starting w/ #!) to
75 contain the correct full pathname of sh.</p></li>
77 <li><p>Make "build" and "install" directories as siblings of the "src"
81 /usr/local/example/cfrontend/src
84 % set CFEINSTALL = `pwd`/install
87 <li><p>Configure, build and install the C front-end:</p>
90 % ../src/configure --prefix=$CFEINSTALL --disable-nls --disable-shared \
91 --enable-languages=c,c++
93 % setenv LLVM_LIB_SEARCH_PATH `pwd`/gcc
94 % gmake all; gmake install
97 <p><b>Common Problem:</b> You may get error messages regarding the fact
98 that LLVM does not support inline assembly. Here are two common
102 <li><p><b>Fix 1:</b> If you have system header files that include
103 inline assembly, you may have to modify them to remove the inline
104 assembly, and install the modified versions in
105 <code>$CFEINSTALL/<i>target-triplet</i>/sys-include</code>.</p></li>
107 <li><b>Fix 2:</b> If you are building the C++ front-end on a CPU we
108 haven't tried yet, you will probably have to edit the appropriate
109 version of atomicity.h under
110 <code>src/libstdc++-v3/config/cpu/<i>name-of-cpu</i>/atomicity.h</code>
111 and apply a patch so that it does not use inline assembly.</p></li>
114 <p><b>Porting to a new architecture:</b> If you are porting the new front-end
115 to a new architecture, or compiling in a different configuration that we have
116 previously, there are probably several changes you will have to make to the GCC
117 target to get it to work correctly. These include:<p>
120 <li>Often targets include special or assembler linker flags which
121 <tt>gccas</tt>/<tt>gccld</tt> does not understand. In general, these can
122 just be removed.</li>
123 <li>LLVM currently does not support any floating point values other than
124 32-bit and 64-bit IEEE floating point. The primary effect of this is
125 that you may have to map "long double" onto "double".</li>
126 <li>The profiling hooks in GCC do not apply at all to the LLVM front-end.
127 These may need to be disabled.</li>
128 <li>No inline assembly for position independent code. At the LLVM level,
129 everything is position independent.</li>
130 <li>We handle <tt>.init</tt> and <tt>.fini</tt> differently.</li>
131 <li>You may have to disable multilib support in your target. Using multilib
132 support causes the GCC compiler driver to add a lot of "<tt>-L</tt>"
133 options to the link line, which do not relate to LLVM and confuse
134 <tt>gccld</tt>. To disable multilibs, delete any
135 <tt>MULTILIB_OPTIONS</tt> lines from your target files.</li>
136 <li>Did we mention that we don't support inline assembly? You'll probably
137 have to add some fixinclude hacks to disable it in the system
142 <li><p>Go back into the LLVM source tree proper. Edit Makefile.config
143 to redefine <code>LLVMGCCDIR</code> to the full pathname of the
144 <code>$CFEINSTALL</code> directory, which is the directory you just
145 installed the C front-end into. (The ./configure script is likely to
146 have set this to a directory which does not exist on your system.)</p></li>
148 <li><p>If you edited header files during the C/C++ front-end build as
149 described in "Fix 1" above, you must now copy those header files from
150 <code>$CFEINSTALL/<i>target-triplet</i>/sys-include</code> to
151 <code>$CFEINSTALL/lib/gcc/<i>target-triplet</i>/3.4-llvm/include</code>.
152 (This should be the "include" directory in the same directory as the
153 libgcc.a library, which you can find by running
154 <code>$CFEINSTALL/bin/gcc --print-libgcc-file-name</code>.)</p></li>
156 <li><p>Build and install the runtime (bytecode) libraries by running:</p>
159 % mkdir $CFEINSTALL/bytecode-libs
160 % gmake -C runtime install
161 % setenv LLVM_LIB_SEARCH_PATH $CFEINSTALL/bytecode-libs
164 <li><p>Test the newly-installed C frontend by one or more of the
167 <li> compiling and running a "hello, LLVM" program in C and C++.</li>
168 <li> running the tests under <tt>test/Programs</tt> using <code>gmake -C
169 test/Programs</code></li>
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179 <div class="doc_footer">
180 <address>Brian Gaeke</address>
181 <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
183 Last modified: $Date$