1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
3 <!-- Material used from: HTML 4.01 specs: http://www.w3.org/TR/html401/ -->
6 <META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
7 <title>Hacking on clang</title>
8 <link type="text/css" rel="stylesheet" href="menu.css" />
9 <link type="text/css" rel="stylesheet" href="content.css" />
12 <!--#include virtual="menu.html.incl"-->
14 <!--*********************************************************************-->
15 <h1>Hacking on Clang</h1>
16 <!--*********************************************************************-->
18 <p>This document provides some hints for how to get started hacking
19 on Clang for developers who are new to the Clang and/or LLVM
22 <li><a href="#style">Coding Standards</a></li>
23 <li><a href="#docs">Developer Documentation</a></li>
24 <li><a href="#debugging">Debugging</a></li>
25 <li><a href="#testing">Testing</a></li>
27 <li><a href="#testingNonWindows">Testing on Unix-like Systems</a></li>
28 <li><a href="#testingWindows">Testing using Visual Studio on Windows</a></li>
29 <li><a href="#testingCommands">Testing on the Command Line</a></li>
31 <li><a href="#patches">Creating Patch Files</a></li>
32 <li><a href="#irgen">LLVM IR Generation</a></li>
35 <!--=====================================================================-->
36 <h2 id="docs">Coding Standards</h2>
37 <!--=====================================================================-->
40 LLVM <a href="http://llvm.org/docs/CodingStandards.html">Coding
41 Standards</a>. When submitting patches, please take care to follow these standards
42 and to match the style of the code to that present in Clang (for example, in
43 terms of indentation, bracing, and statement spacing).</p>
45 <p>Clang has a few additional coding standards:</p>
47 <li><i>cstdio is forbidden</i>: library code should not output diagnostics
48 or other information using <tt>cstdio</tt>; debugging routines should
49 use <tt>llvm::errs()</tt>. Other uses of <tt>cstdio</tt> impose behavior
50 upon clients and block integrating Clang as a library. Libraries should
51 support <tt>raw_ostream</tt> based interfaces for textual
52 output. See <a href="http://llvm.org/docs/CodingStandards.html#ll_raw_ostream">Coding
56 <!--=====================================================================-->
57 <h2 id="docs">Developer Documentation</h2>
58 <!--=====================================================================-->
60 <p>Both Clang and LLVM use doxygen to provide API documentation. Their
61 respective web pages (generated nightly) are here:</p>
63 <li><a href="http://clang.llvm.org/doxygen">Clang</a></li>
64 <li><a href="http://llvm.org/doxygen">LLVM</a></li>
67 <p>For work on the LLVM IR generation, the LLVM assembly language
68 <a href="http://llvm.org/docs/LangRef.html">reference manual</a> is
71 <!--=====================================================================-->
72 <h2 id="debugging">Debugging</h2>
73 <!--=====================================================================-->
75 <p>Inspecting data structures in a debugger:</p>
77 <li>Many LLVM and Clang data structures provide
78 a <tt>dump()</tt> method which will print a description of the
79 data structure to <tt>stderr</tt>.</li>
80 <li>The <a href="docs/InternalsManual.html#QualType"><tt>QualType</tt></a>
81 structure is used pervasively. This is a simple value class for
82 wrapping types with qualifiers; you can use
83 the <tt>isConstQualified()</tt>, for example, to get one of the
84 qualifiers, and the <tt>getTypePtr()</tt> method to get the
85 wrapped <tt>Type*</tt> which you can then dump.</li>
88 <!--=====================================================================-->
89 <h2 id="testing">Testing</h2>
90 <!--=====================================================================-->
92 <p><i>[Note: The test running mechanism is currently under revision, so the
93 following might change shortly.]</i></p>
95 <!--=====================================================================-->
96 <h3 id="testingNonWindows">Testing on Unix-like Systems</h3>
97 <!--=====================================================================-->
99 <p>Clang includes a basic regression suite in the tree which can be
100 run with <tt>make test</tt> from the top-level clang directory, or
101 just <tt>make</tt> in the <em>test</em> sub-directory.
102 <tt>make VERBOSE=1</tt> can be used to show more detail
103 about what is being run.</p>
105 <p>If you built LLVM and Clang using CMake, the test suite can be run
106 with <tt>make clang-test</tt> from the top-level LLVM directory.</p>
108 <p>The tests primarily consist of a test runner script running the compiler
109 under test on individual test files grouped in the directories under the
110 test directory. The individual test files include comments at the
111 beginning indicating the Clang compile options to use, to be read
112 by the test runner. Embedded comments also can do things like telling
113 the test runner that an error is expected at the current line.
114 Any output files produced by the test will be placed under
115 a created Output directory.</p>
117 <p>During the run of <tt>make test</tt>, the terminal output will
118 display a line similar to the following:</p>
120 <ul><tt>--- Running clang tests for i686-pc-linux-gnu ---</tt></ul>
122 <p>followed by a line continually overwritten with the current test
123 file being compiled, and an overall completion percentage.</p>
125 <p>After the <tt>make test</tt> run completes, the absence of any
126 <tt>Failing Tests (count):</tt> message indicates that no tests
127 failed unexpectedly. If any tests did fail, the
128 <tt>Failing Tests (count):</tt> message will be followed by a list
129 of the test source file paths that failed. For example:</p>
133 /home/john/llvm/tools/clang/test/SemaCXX/member-name-lookup.cpp
134 /home/john/llvm/tools/clang/test/SemaCXX/namespace-alias.cpp
135 /home/john/llvm/tools/clang/test/SemaCXX/using-directive.cpp
138 <p>If you used the <tt>make VERBOSE=1</tt> option, the terminal
139 output will reflect the error messages from the compiler and
142 <p>The regression suite can also be run with Valgrind by running
143 <tt>make test VG=1</tt> in the top-level clang directory.</p>
145 <p>For more intensive changes, running
146 the <a href="http://llvm.org/docs/TestingGuide.html#testsuiterun">LLVM
147 Test Suite</a> with clang is recommended. Currently the best way to
148 override LLVMGCC, as in: <tt>make LLVMGCC="clang -std=gnu89"
149 TEST=nightly report</tt> (make sure <tt>clang</tt> is in your PATH or use the
152 <!--=====================================================================-->
153 <h3 id="testingWindows">Testing using Visual Studio on Windows</h3>
154 <!--=====================================================================-->
156 <p>The Clang test suite can be run from either Visual Studio or
157 the command line.</p>
159 <p>Note that the test runner is based on
160 Python, which must be installed. Find Python at:
161 <a href="http://www.python.org/download/">http://www.python.org/download/</a>.
162 Download the latest stable version (2.6.2 at the time of this writing).</p>
164 <p>The GnuWin32 tools are also necessary for running the tests.
165 Get them from <a href="http://getgnuwin32.sourceforge.net/">
166 http://getgnuwin32.sourceforge.net/</a>.
167 If the environment variable <tt>%PATH%</tt> does not have GnuWin32,
168 or if other grep(s) supercedes GnuWin32 on <tt>%PATH%,</tt>
169 you should specify <tt>LLVM_LIT_TOOLS_DIR</tt>
170 to CMake explicitly.</p>
172 <p>The cmake build tool is set up to create Visual Studio project files
173 for running the tests, "clang-test" being the root. Therefore, to
174 run the test from Visual Studio, right-click the clang-test project
175 and select "Build".</p>
179 <a href="http://llvm.org/docs/GettingStartedVS.html">Getting Started
180 with the LLVM System using Microsoft Visual Studio</a> and
181 <a href="http://llvm.org/docs/CMake.html">Building LLVM with CMake</a>.
184 <!--=====================================================================-->
185 <h3 id="testingCommands">Testing on the Command Line</h3>
186 <!--=====================================================================-->
188 <p>To run all the tests from the command line, execute a command like
192 python (path to llvm)/llvm/utils/lit/lit.py -sv --no-progress-bar
193 (path to llvm)/llvm/tools/clang/test
196 <p>For CMake builds e.g. on Windows with Visual Studio, you will need
197 to specify your build configuration (Debug, Release, etc.) via
198 <tt>--param=build_config=(build config)</tt>.</p>
200 <p>To run a single test:</p>
203 python (path to llvm)/llvm/utils/lit/lit.py -sv --no-progress-bar
204 (path to llvm)/llvm/tools/clang/test/(dir)/(test)
210 python C:/Tools/llvm/utils/lit/lit.py -sv --no-progress-bar
211 C:/Tools/llvm/tools/clang/test/Sema/wchar.c
214 <p>The -sv option above tells the runner to show the test output if
215 any tests failed, to help you determine the cause of failure.</p>
217 <p>Your output might look something like this:</p>
219 <tt><pre>lit.py: lit.cfg:152: note: using clang: 'C:/Tools/llvm/bin/Release\\clang.EXE'
220 -- Testing: Testing: 2534 tests, 4 threads --
221 Testing: 0 .. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90..
223 Expected Passes : 2503
224 Expected Failures : 28
225 Unsupported Tests : 3
228 <p>The statistic, "Unexpected Failures" (not shown if all tests pass), is the important one.</p>
230 <!--=====================================================================-->
231 <h2 id="patches">Creating Patch Files</h2>
232 <!--=====================================================================-->
234 <p>To return changes to the Clang team, unless you have checkin
235 privileges, the preferred way is to send patch files to the
236 cfe-commits mailing list, with an explanation of what the patch is for.
237 Or, if you have questions, or want to have a wider discussion of what
238 you are doing, such as if you are new to Clang development, you can use
239 the cfe-dev mailing list also.
242 <p>To create these patch files, change directory
243 to the llvm/tools/clang root and run:</p>
245 <ul><tt>svn diff (relative path) >(patch file name)</tt></ul>
247 <p>For example, for getting the diffs of all of clang:</p>
249 <ul><tt>svn diff . >~/mypatchfile.patch</tt></ul>
251 <p>For example, for getting the diffs of a single file:</p>
253 <ul><tt>svn diff lib/Parse/ParseDeclCXX.cpp >~/ParseDeclCXX.patch</tt></ul>
255 <p>Note that the paths embedded in the patch depend on where you run it,
256 so changing directory to the llvm/tools/clang directory is recommended.</p>
258 <!--=====================================================================-->
259 <h2 id="irgen">LLVM IR Generation</h2>
260 <!--=====================================================================-->
262 <p>The LLVM IR generation part of clang handles conversion of the
263 AST nodes output by the Sema module to the LLVM Intermediate
264 Representation (IR). Historically, this was referred to as
265 "codegen", and the Clang code for this lives
266 in <tt>lib/CodeGen</tt>.</p>
268 <p>The output is most easily inspected using the <tt>-emit-llvm</tt>
269 option to clang (possibly in conjunction with <tt>-o -</tt>). You
270 can also use <tt>-emit-llvm-bc</tt> to write an LLVM bitcode file
271 which can be processed by the suite of LLVM tools
272 like <tt>llvm-dis</tt>, <tt>llvm-nm</tt>, etc. See the LLVM
273 <a href="http://llvm.org/docs/CommandGuide/">Command Guide</a>
274 for more information.</p>