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<div id="content">

<h1>Getting Involved</h1>
<h1>Getting Involved with the Clang Project</h1>

<p>There are many tasks that are open to new developers who want to get involved
with the Clang project. Below, you will find details on how to get started with
Clang, plus a few tasks that we need help with.</p>
<p>Once you have <a href="get_started.html">checked out and built</a> clang and
played around with it, you might be wondering what you can do to make it better
and contribute to its development. Alternatively, maybe you just want to follow
the development of the project to see it progress.
</p>

<p>Please note that the information provided here is not completely thorough.
This is intentional. If you plan to work on Clang, we would like you to get
involved with the other developers. This will allow us to work together better
and will give you a better feel for how things are done.</p>

<p>You can talk with other developers at the following mailing list: <a
href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">cfe-dev mailing
list</a>. The clang mailing list is a very friendly place. You can see the
archives for records of past discussion. Note that a significant amount of
design discussion takes place on the <a
href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits">cfe-commits mailing
list</a>. </p>

<h2>Getting Started</h2>

<h3>A word of warning</h3>
<h2>Follow what's going on</h2>

<p>While this work aims to provide a fully functional C/C++/ObjC front-end, it
is <em>still very early work</em> and is under heavy development. In particular,
there is no real C++ support yet (this is obviously a big project), and C/ObjC
support is still missing some features. Some of the more notable missing pieces
of C support are:</p>
<p>Clang is a subproject of the <a href="http://llvm.org">LLVM Project</a>, but
has its own mailing lists because the communities have people with different
interests. The two clang lists are:</p>

<ol>
<li>The semantic analyzer does not produce all of the warnings and errors it
should.</li>
<li>The LLVM code generator is still very early on. It does not support many
important things, like any support for structs and unions. That said, it
does handle scalar operations and vectors. clang is not ready to be used
as a general purpose C code generator yet.</li>
<li>We don't consider the API to be stable yet, and reserve the right to
change fundamental things. :)</li>
</ol>
<ul>
<li><a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits">cfe-commits
</a> - This list is for patch submission/discussion.</li>

<p>Our plan is to continue chipping away at these issues until C works really
well, but we'd love help from other interested contributors.</p>
<li><a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">cfe-dev</a> -
This list is for everything else clang related (questions and answers, bug
reports, etc).</li>

<h3>Follow what's going on</h3>
</ul>

<p>Clang is a subproject of the <a href="http://llvm.org">LLVM Project</a>, but
has its own mailing lists because the communities have people with different
interests. If you are interested in clang only, these two lists should be all
<p>If you are interested in clang only, these two lists should be all
you need. If you are interested in the LLVM optimizer and code generator,
please consider signing up for <a
href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a> and <a
href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
as well.</p>

<ul>
<li><a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits">cfe-commits
</a> - This list is for patch submission/discussion.</li>

<li><a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">cfe-dev</a> -
This list is for everything else clang related.</li>
</ul>
<p>The best way to talk with other developers on the project is through the <a
href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">cfe-dev mailing
list</a>. The clang mailing list is a very friendly place and we welcome
newcomers. In addition to the cfe-dev list, a significant amount of design
discussion takes place on the <a
href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits">cfe-commits mailing
list</a>. All of these lists have archives, so you can browse through previous
discussions or follow the list development on the web if you prefer.</p>


<h2>Open Projects</h2>

<p>Here are a few tasks that are available for newcomers to work on. This list
is provided to generate ideas, it is not intended to be comprehensive. Please
ask on cfe-dev for more specifics or to verify that one of these isn't already
completed. :)</p>

<p>Please note that the information provided here is not completely thorough.
This is intentional. If you plan to work on Clang, we would like you to get
involved with the other developers. This will allow us to work together better
and will give you a better feel for how things are done.</p>

<h3><a name="build">Building clang / working with the code</a></h3>

<p>If you would like to check out and build the project, the current scheme
is:</p>

<ol>
<li><a href="http://www.llvm.org/docs/GettingStarted.html#checkout">Checkout
and build LLVM</a> from SVN head:</li>

<ul>
<li><tt>svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm</tt></li>
<li><tt>cd llvm</tt></li>
<li><tt>./configure; make</tt></li>
</ul>
<li>Checkout clang:</li>
<ul>
<li>From within the <tt>llvm</tt> directory (where you
built llvm):</li>
<li><tt>cd llvm/tools</tt>
<li><tt>svn co
http://llvm.org/svn/llvm-project/cfe/trunk clang</tt></li>

</ul>
<li>Non-mac users: Paths to system header files are currently hard coded
into clang; as a result, if clang can't find your system headers,
please follow these instructions:</li>

<ul>
<li>'<tt>touch empty.c; gcc -v empty.c -fsyntax-only</tt>' to get the
path.</li>
<li>Look for the comment "FIXME: temporary hack:
hard-coded paths" in <tt>clang/Driver/clang.cpp</tt> and
change the lines below to include that path.</li>
</ul>

<li>Build clang:</li>
<ul>
<li><tt>cd clang</tt> (assuming that you are in <tt>llvm/tools</tt>)</li>
<li><tt>make</tt></li>
</ul>

<li>Try it out (assuming you add llvm/Debug/bin to your path):</li>
<ul>
<li><tt>clang --help</tt></li>
<li><tt>clang file.c -fsyntax-only</tt> (check for correctness)</li>
<li><tt>clang file.c -ast-dump</tt> (internal debug dump of ast)</li>
<li><tt>clang file.c -ast-view</tt> (<a
href="http://llvm.org/docs/ProgrammersManual.html#ViewGraph">set up graphviz
and rebuild llvm first</a>)</li>
<li><tt>clang file.c -emit-llvm</tt> (print out unoptimized llvm code)</li>
<li><tt>clang file.c -emit-llvm | llvm-as | opt -std-compile-opts |
llvm-dis</tt> (print out optimized llvm code)</li>
<li><tt>clang file.c -emit-llvm | llvm-as | opt -std-compile-opts | llc
&gt; file.s</tt> (output native machine code)</li>
</ul>
</ol>

<p>Note that the C front-end uses LLVM, but does not depend on
llvm-gcc. If you encounter problems with building clang, make
sure you have the latest SVN version of LLVM. LLVM contains
support libraries for clang that will be updated as well as
development on clang progresses.</p>

<h3>Examples of using clang</h3>

<p>The clang driver takes a lot of GCC compatible options, which you can see
with 'clang --help'. Here are a few examples:</p>
<!-- Thanks to
http://shiflett.org/blog/2006/oct/formatting-and-highlighting-php-code-listings
Site suggested using pre in CSS, but doesn't work in IE, so went for the <pre>
tag. -->

<pre class="code">
$ cat ~/t.c

typedef float V __attribute__((vector_size(16)));
V foo(V a, V b) { return a+b*a; }

Preprocessing:
$ clang ~/t.c -E
# 1 "/Users/sabre/t.c" 1

typedef float V __attribute__((vector_size(16)));

V foo(V a, V b) { return a+b*a; }


Type checking:
$ clang -fsyntax-only ~/t.c


GCC options:
$ clang -fsyntax-only ~/t.c -pedantic
/Users/sabre/t.c:2:17: warning: extension used
typedef float V __attribute__((vector_size(16)));
^
1 diagnostic generated.



Pretty printing from the AST:
$ clang ~/t.c -ast-print
typedef float V __attribute__(( vector_size(16) ));

V foo(V a, V b) {
return a + b * a;
}


LLVM code generation:
$ clang ~/t.c -emit-llvm | llvm-as | opt -std-compile-opts | llvm-dis
define &lt;4 x float&gt; @foo(&lt;4 x float&gt; %a, &lt;4 x float&gt; %b) {
entry:
%mul = mul &lt;4 x float&gt; %b, %a
%add = add &lt;4 x float&gt; %mul, %a
ret &lt;4 x float&gt; %add
}
$ clang ~/t.c -emit-llvm | llvm-as | opt -std-compile-opts | llc -
march=ppc32 -mcpu=g5
..
_foo:
vmaddfp v2, v3, v2, v2
blr
$ clang ~/t.c -emit-llvm | llvm-as | opt -std-compile-opts | llc -
march=x86 -mcpu=yonah
..
_foo:
mulps %xmm0, %xmm1
addps %xmm0, %xmm1
movaps %xmm1, %xmm0
ret
</pre>
<h2>Available tasks</h2>
Here are a few tasks that are currently available for newcomers to work on:

<ul>
<li>None yet, ask on cfe-dev</li>
<li><b>Compile your favorite C/ObjC project with "clang -fsyntax-only"</b>:
the clang type checker and verifier is quite close to complete (but not bug
free!) for C and Objective C. We appreciate all reports of code that is
rejected by the front-end, and if you notice invalid code that is not rejected
by clang, that is also very important to us.</li>

<li>

</li>
</ul>

</div>
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