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John Criswellc310f622003-10-13 16:13:06 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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3<h1>
4<center>
5LLVM: Frequently Asked Questions
6</center>
7</h1>
8
9<hr>
10
11<!--=====================================================================-->
12<h2>
Vikram S. Adve04da65a2003-10-25 17:06:55 +0000[diff] [blame]13<a name="license">Licenses</a>
14</h2>
15<!--=====================================================================-->
16
17<dl compact>
18 <dt> <b>Why are the LLVM source code and the front-end distributed
19 under different licenses?</b>
20 <dd>
21 The C/C++ front-ends are based on GCC and must be distributed under
Vikram S. Adve0493f342003-10-25 17:19:21 +0000[diff] [blame]22 the GPL. Our aim is to distribute LLVM source code under a <em>much
Vikram S. Adve04da65a2003-10-25 17:06:55 +0000[diff] [blame]23 less restrictive</em> license, in particular one that does not
24 compel users who distribute tools based on modifying the source to
25 redistribute the modified source code as well.
Vikram S. Adve168da7d2003-10-25 17:14:52 +0000[diff] [blame]26 <p>
Misha Brukman32a32f02003-10-30 01:13:56 +0000[diff] [blame^]27 <dt><b>Does the University of Illinois Open Source License really qualify
Vikram S. Adve04da65a2003-10-25 17:06:55 +0000[diff] [blame]28 as an "open source" license?</b>
Vikram S. Adve58433c42003-10-25 17:22:08 +0000[diff] [blame]29 <dd>The license is
30 <a href="http://www.opensource.org/licenses/UoI-NCSA.php">certified</a>
31 by the Open Source Initiative (OSI).
Vikram S. Adve168da7d2003-10-25 17:14:52 +0000[diff] [blame]32 <p>
Vikram S. Adve04da65a2003-10-25 17:06:55 +0000[diff] [blame]33 <dt> <b>Can I modify LLVM source code and redistribute the modified
34 source?</b>
35 <dd>
Vikram S. Adve0493f342003-10-25 17:19:21 +0000[diff] [blame]36 Yes. The modified source distribution must retain the
Vikram S. Adve04da65a2003-10-25 17:06:55 +0000[diff] [blame]37 copyright notice and follow the three bulletted conditions listed in
Vikram S. Adve6d376792003-10-25 17:20:38 +0000[diff] [blame]38 the <a href="http://llvm.cs.uiuc.edu/releases/1.0/LICENSE.TXT">LLVM license</a>.
Vikram S. Adve168da7d2003-10-25 17:14:52 +0000[diff] [blame]39 <p>
Vikram S. Adve04da65a2003-10-25 17:06:55 +0000[diff] [blame]40 <dt> <b>Can I modify LLVM source code and redistribute binaries or
Vikram S. Adve168da7d2003-10-25 17:14:52 +0000[diff] [blame]41 other tools based on it, without redistributing the source?</b>
Vikram S. Adve04da65a2003-10-25 17:06:55 +0000[diff] [blame]42 <dd>
43 Yes, this is why we distribute LLVM under a less restrictive license
44 than GPL, as explained in the first question above.
45 <p>
46</dl>
47<hr>
48
49<!--=====================================================================-->
50<h2>
John Criswellc310f622003-10-13 16:13:06 +0000[diff] [blame]51<a name="source">Source Code</a>
52</h2>
53<!--=====================================================================-->
54
55<dl compact>
56 <dt> <b>In what language is LLVM written?</b>
57 <dd>
58 All of the LLVM tools and libraries are written in C++ with extensive use
59 of the STL.
60 <p>
61
62 <dt><b>How portable is the LLVM source code?</b>
63 <dd>
64 The LLVM source code should be portable to most modern UNIX-like operating
65 systems. Most of the code is written in standard C++ with operating
66 system services abstracted to a support library. The tools required to
67 build and test LLVM have been ported to a plethora of platforms.
68 <p>
69 Some porting problems may exist in the following areas:
70 <ul>
71 <li>The GCC front end code is not as portable as the LLVM suite, so it
72 may not compile as well on unsupported platforms.
73
74 <p>
75
76 <li>The Python test classes are more UNIX-centric than they should be,
77 so porting to non-UNIX like platforms (i.e. Windows, MacOS 9) will
78 require some effort.
79 <p>
80
81 <li>The LLVM build system relies heavily on UNIX shell tools, like the
82 Bourne Shell and sed. Porting to systems without these tools (MacOS 9,
83 Plan 9) will require more effort.
84 </ul>
85</dl>
86
87<hr>
88
89<!--=====================================================================-->
90<h2>
91<a name="build">Build Problems</a>
92</h2>
93<!--=====================================================================-->
94
95<dl compact>
96 <dt><b>When I run configure, it finds the wrong C compiler.</b>
97 <dd>
98 The <tt>configure</tt> script attempts to locate first <tt>gcc</tt> and
99 then <tt>cc</tt>, unless it finds compiler paths set in <tt>CC</tt> and
100 <tt>CXX</tt> for the C and C++ compiler, respectively.
101
102 If <tt>configure</tt> finds the wrong compiler, either adjust your
103 <tt>PATH</tt> environment variable or set <tt>CC</tt> and <tt>CXX</tt>
104 explicitly.
105 <p>
106
107 <dt><b>I compile the code, and I get some error about /localhome</b>.
108 <dd>
109 There are several possible causes for this. The first is that you
110 didn't set a pathname properly when using <tt>configure</tt>, and it
111 defaulted to a pathname that we use on our research machines.
112 <p>
113 Another possibility is that we hardcoded a path in our Makefiles. If
114 you see this, please email the LLVM bug mailing list with the name of
115 the offending Makefile and a description of what is wrong with it.
116
117 <dt><b>The <tt>configure</tt> script finds the right C compiler, but it
118 uses the LLVM linker from a previous build. What do I do?</b>
119 <dd>
120 The <tt>configure</tt> script uses the <tt>PATH</tt> to find
121 executables, so if it's grabbing the wrong linker/assembler/etc, there
122 are two ways to fix it:
123 <ol>
124 <li>Adjust your <tt>PATH</tt> environment variable so that the
125 correct program appears first in the <tt>PATH</tt>. This may work,
126 but may not be convenient when you want them <i>first</i> in your
127 path for other work.
128 <p>
129
130 <li>Run <tt>configure</tt> with an alternative <tt>PATH</tt> that
131 is correct. In a Borne compatible shell, the syntax would be:
132 <p>
133 <tt>PATH=<the path without the bad program> ./configure ...</tt>
134 <p>
135 This is still somewhat inconvenient, but it allows
136 <tt>configure</tt> to do its work without having to adjust your
137 <tt>PATH</tt> permanently.
138 </ol>
139
140 <dt><b>When creating a dynamic library, I get a strange GLIBC error.</b>
141 <dd>
142 Under some operating systems (i.e. Linux), libtool does not work correctly
143 if GCC was compiled with the --disable-shared option. To work around this,
144 install your own version of GCC that has shared libraries enabled by
145 default.
146 <p>
147
148 <dt><b>I've updated my source tree from CVS, and now my build is trying to
149 use a file/directory that doesn't exist.</b>
150 <dd>
151 You need to re-run configure in your object directory. When new Makefiles
152 are added to the source tree, they have to be copied over to the object
153 tree in order to be used by the build.
154 <p>
155
156 <dt><b>I've modified a Makefile in my source tree, but my build tree keeps
157 using the old version. What do I do?</b>
158 <dd>
159 If the Makefile already exists in your object tree, you can just run the
160 following command in the top level directory of your object tree:
161 <p>
162 <tt>./config.status &lt;relative path to Makefile&gt;</tt>
163 <p>
164 If the Makefile is new, you will have to modify the configure script to copy
165 it over.
166 <p>
167
168 <dt><b>I've upgraded to a new version of LLVM, and I get strange build
169 errors.</b>
170 <dd>
171 Sometimes changes to the LLVM source code alters how the build system
172 works. Changes in libtool, autoconf, or header file dependencies are
173 especially prone to this sort of problem.
174 <p>
175 The best thing to try is to remove the old files and re-build. In most
176 cases, this takes care of the problem. To do this, just type <tt>make
177 clean</tt> and then <tt>make</tt> in the directory that fails to build.
178 <p>
John Criswellf08c5d82003-10-24 22:48:20 +0000[diff] [blame]179
180 <dt><b>I've built LLVM and am testing it, but the tests freeze.</b>
181 <dd>
182 This is most likely occurring because you built a profile or release
183 (optimized) build of LLVM and have not specified the same information on
184 the <tt>gmake</tt> command line.
185 <p>
186 For example, if you built LLVM with the command:
187 <p>
188 <tt>gmake ENABLE_PROFILING=1</tt>
189 <p>
190 ...then you must run the tests with the following commands:
191 <p>
192 <tt>cd llvm/test<br>gmake ENABLE_PROFILING=1</tt>
193 <p>
194
195 <dt><b>Why do test results differ when I perform different types of
196 builds?</b>
197 <dd>
198 The LLVM test suite is dependent upon several features of the LLVM tools
199 and libraries.
200 <p>
201 First, the debugging assertions in code are not enabled in optimized or
202 profiling builds. Hence, tests that used to fail may pass.
203 <p>
204 Second, some tests may rely upon debugging options or behavior that is
205 only available in the debug build. These tests will fail in an optimized
206 or profile build.
John Criswellc310f622003-10-13 16:13:06 +0000[diff] [blame]207</dl>
208<hr>
209
John Criswellf08c5d82003-10-24 22:48:20 +0000[diff] [blame]210<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
211<br>
212
John Criswellc310f622003-10-13 16:13:06 +0000[diff] [blame]213</body>
214</html>