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| 6 | <title>Clang - Get Involved</title> |
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| 15 | |
| 16 | <h1>Getting Involved with the Clang Project</h1> |
| 17 | |
| 18 | <p>Once you have <a href="get_started.html">checked out and built</a> clang and |
| 19 | played around with it, you might be wondering what you can do to make it better |
| 20 | and contribute to its development. Alternatively, maybe you just want to follow |
| 21 | the development of the project to see it progress. |
| 22 | </p> |
| 23 | |
| 24 | <h2>Follow what's going on</h2> |
| 25 | |
| 26 | <p>Clang is a subproject of the <a href="http://llvm.org">LLVM Project</a>, but |
| 27 | has its own mailing lists because the communities have people with different |
| 28 | interests. The two clang lists are:</p> |
| 29 | |
| 30 | <ul> |
| 31 | <li><a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits">cfe-commits |
| 32 | </a> - This list is for patch submission/discussion.</li> |
| 33 | |
| 34 | <li><a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">cfe-dev</a> - |
| 35 | This list is for everything else clang related (questions and answers, bug |
| 36 | reports, etc).</li> |
| 37 | |
| 38 | </ul> |
| 39 | |
| 40 | <p>If you are interested in clang only, these two lists should be all |
| 41 | you need. If you are interested in the LLVM optimizer and code generator, |
| 42 | please consider signing up for <a |
| 43 | href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a> and <a |
| 44 | href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a> |
| 45 | as well.</p> |
| 46 | |
| 47 | |
| 48 | <p>The best way to talk with other developers on the project is through the <a |
| 49 | href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">cfe-dev mailing |
| 50 | list</a>. The clang mailing list is a very friendly place and we welcome |
| 51 | newcomers. In addition to the cfe-dev list, a significant amount of design |
| 52 | discussion takes place on the <a |
| 53 | href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits">cfe-commits mailing |
| 54 | list</a>. All of these lists have archives, so you can browse through previous |
| 55 | discussions or follow the list development on the web if you prefer.</p> |
| 56 | |
| 57 | |
| 58 | <h2>Open Projects</h2> |
| 59 | |
| 60 | <p>Here are a few tasks that are available for newcomers to work on, depending |
| 61 | on what your interests are. This list is provided to generate ideas, it is not |
| 62 | intended to be comprehensive. Please ask on cfe-dev for more specifics or to |
| 63 | verify that one of these isn't already completed. :)</p> |
| 64 | |
| 65 | <ul> |
| 66 | <li><b>Compile your favorite C/ObjC project with "clang -fsyntax-only"</b>: |
| 67 | the clang type checker and verifier is quite close to complete (but not bug |
| 68 | free!) for C and Objective C. We appreciate all reports of code that is |
| 69 | rejected by the front-end, and if you notice invalid code that is not rejected |
| 70 | by clang, that is also very important to us. For make-based projects, |
| 71 | the <a href="get_started.html#ccc"><code>ccc</code></a> script in clang's |
| 72 | <tt>utils</tt> folder might help to get you started.</li> |
| 73 | |
| 74 | <li><b>Compile your favorite C project with "clang -emit-llvm"</b>: |
| 75 | The clang to LLVM converter is getting more mature, so you may be able to |
| 76 | compile it. If not, please let us know. Again, |
| 77 | <a href="get_started.html#ccc"><code>ccc</code></a> might help you. Once it |
| 78 | compiles it should run. If not, that's a bug :)</li> |
| 79 | |
| 80 | <li><b>Debug Info Generation</b>: -emit-llvm doesn't fully support emission |
| 81 | of <a href="http://llvm.org/docs/SourceLevelDebugging.html">LLVM debug info</a> |
| 82 | (which the code generator turns into DWARF). The missing pieces are pretty |
| 83 | minor at this point.</li> |
| 84 | |
| 85 | <li><b>Overflow detection</b>: an interesting project would be to add a -ftrapv |
| 86 | compilation mode that causes -emit-llvm to generate overflow tests for all |
| 87 | signed integer arithmetic operators, and call abort if they overflow. Overflow |
| 88 | is undefined in C and hard for people to reason about. LLVM IR also has |
| 89 | intrinsics for generating arithmetic with overflow checks directly.</li> |
| 90 | |
| 91 | <li><b>Undefined behavior checking</b>: similar to adding -ftrapv, codegen could |
| 92 | insert runtime checks for all sorts of different undefined behaviors, from |
| 93 | reading uninitialized variables, buffer overflows, and many other things. This |
| 94 | checking would be expensive, but the optimizers could eliminate many of the |
| 95 | checks in some cases, and it would be very interesting to test code in this mode |
| 96 | for certain crowds of people. Because the inserted code is coming from clang, |
| 97 | the "abort" message could be very detailed about exactly what went wrong.</li> |
| 98 | |
| 99 | <li><b>Continue work on C++ support</b>: Implementing all of C++ is a very big |
| 100 | job, but there are lots of little pieces that can be picked off and implemented. |
| 101 | See the <a href="cxx_status.html">C++ status report page</a> to find out what is |
| 102 | missing and what is already at least partially supported.</li> |
| 103 | |
| 104 | <li><b>Improve target support</b>: The current target interfaces are heavily |
| 105 | stubbed out and need to be implemented fully. See the FIXME's in TargetInfo. |
| 106 | Additionally, the actual target implementations (instances of TargetInfoImpl) |
| 107 | also need to be completed. This includes defining builtin macros for linux |
| 108 | targets and other stuff like that.</li> |
| 109 | |
| 110 | <li><b>Implement 'builtin' headers</b>: GCC provides a bunch of builtin headers, |
| 111 | such as stdbool.h, iso646.h, float.h, limits.h, etc. It also provides a bunch |
| 112 | of target-specific headers like altivec.h and xmmintrin.h. clang will |
| 113 | eventually need to provide its own copies of these (and there is a <a href= |
| 114 | "http://lists.cs.uiuc.edu/pipermail/cfe-dev/2007-December/000560.html">lot of |
| 115 | improvement</a> that can be made to the GCC ones!) that are clean-room |
| 116 | implemented to avoid GPL taint.</li> |
| 117 | |
| 118 | <li><b>Implement a clang 'libgcc'</b>: As with the headers, clang (or a another |
| 119 | related subproject of llvm) will need to implement the features that libgcc |
| 120 | provides. libgcc provides a bunch of routines the code generator uses for |
| 121 | "fallback" when the chip doesn't support some operation (e.g. 64-bit divide on |
| 122 | a 32-bit chip). It also provides software floating point support and many other |
| 123 | things. I don't think that there is a specific licensing reason to reimplement |
| 124 | libgcc, but there is a lot of room for improvement in it in many |
| 125 | dimensions.</li> |
| 126 | |
| 127 | <li><b>Implement an tool to generate code documentation</b>: Clang's |
| 128 | library-based design allows it to be used by a variety of tools that reason |
| 129 | about source code. One great application of Clang would be to build an |
| 130 | auto-documentation system like doxygen that generates code documentation from |
| 131 | source code. The advantage of using Clang for such a tool is that the tool would |
| 132 | use the same preprocessor/parser/ASTs as the compiler itself, giving it a very |
| 133 | rich understanding of the code.</li> |
| 134 | |
| 135 | <li><b>Use clang libraries to implement better versions of existing tools</b>: |
| 136 | Clang is built as a set of libraries, which means that it is possible to |
| 137 | implement capabilities similar to other source language tools, improving them |
| 138 | in various ways. Two examples are <a href="http://distcc.samba.org/">distcc</a> |
| 139 | and the <a href="http://delta.tigris.org/">delta testcase reduction tool</a>. |
| 140 | The former can be improved to scale better and be more efficient. The later |
| 141 | could also be faster and more efficient at reducing C-family programs if built |
| 142 | on the clang preprocessor.</li> |
| 143 | |
| 144 | <li><b>Use clang libraries to extend Ragel with a JIT</b>: <a |
| 145 | href="http://research.cs.queensu.ca/~thurston/ragel/">Ragel</a> is a state |
| 146 | machine compiler that lets you embed C code into state machines and generate |
| 147 | C code. It would be relatively easy to turn this into a JIT compiler using |
| 148 | LLVM.</li> |
| 149 | |
| 150 | <li><b>Self-testing using clang</b>: There are several neat ways to |
| 151 | improve the quality of clang by self-testing. Some examples: |
| 152 | <ul> |
| 153 | <li>Improve the reliability of AST printing and serialization by |
| 154 | ensuring that the AST produced by clang on an input doesn't change |
| 155 | when it is reparsed or unserialized. |
| 156 | |
| 157 | <li>Improve parser reliability and error generation by automatically |
| 158 | or randomly changing the input checking that clang doesn't crash and |
| 159 | that it doesn't generate excessive errors for small input |
| 160 | changes. Manipulating the input at both the text and token levels is |
| 161 | likely to produce interesting test cases. |
| 162 | </ul> |
| 163 | </li> |
| 164 | |
| 165 | </ul> |
| 166 | |
| 167 | <p>If you hit a bug with clang, it is very useful for us if you reduce the code |
| 168 | that demonstrates the problem down to something small. There are many ways to |
| 169 | do this; ask on cfe-dev for advice.</p> |
| 170 | |
| 171 | </div> |
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| 173 | </html> |