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5LLVM: Frequently Asked Questions
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12<h2>
13<a name="source">Source Code</a>
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17<dl compact>
18 <dt> <b>In what language is LLVM written?</b>
19 <dd>
20 All of the LLVM tools and libraries are written in C++ with extensive use
21 of the STL.
22 <p>
23
24 <dt><b>How portable is the LLVM source code?</b>
25 <dd>
26 The LLVM source code should be portable to most modern UNIX-like operating
27 systems. Most of the code is written in standard C++ with operating
28 system services abstracted to a support library. The tools required to
29 build and test LLVM have been ported to a plethora of platforms.
30 <p>
31 Some porting problems may exist in the following areas:
32 <ul>
33 <li>The GCC front end code is not as portable as the LLVM suite, so it
34 may not compile as well on unsupported platforms.
35
36 <p>
37
38 <li>The Python test classes are more UNIX-centric than they should be,
39 so porting to non-UNIX like platforms (i.e. Windows, MacOS 9) will
40 require some effort.
41 <p>
42
43 <li>The LLVM build system relies heavily on UNIX shell tools, like the
44 Bourne Shell and sed. Porting to systems without these tools (MacOS 9,
45 Plan 9) will require more effort.
46 </ul>
47</dl>
48
49<hr>
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52<h2>
53<a name="build">Build Problems</a>
54</h2>
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57<dl compact>
58 <dt><b>When I run configure, it finds the wrong C compiler.</b>
59 <dd>
60 The <tt>configure</tt> script attempts to locate first <tt>gcc</tt> and
61 then <tt>cc</tt>, unless it finds compiler paths set in <tt>CC</tt> and
62 <tt>CXX</tt> for the C and C++ compiler, respectively.
63
64 If <tt>configure</tt> finds the wrong compiler, either adjust your
65 <tt>PATH</tt> environment variable or set <tt>CC</tt> and <tt>CXX</tt>
66 explicitly.
67 <p>
68
69 <dt><b>I compile the code, and I get some error about /localhome</b>.
70 <dd>
71 There are several possible causes for this. The first is that you
72 didn't set a pathname properly when using <tt>configure</tt>, and it
73 defaulted to a pathname that we use on our research machines.
74 <p>
75 Another possibility is that we hardcoded a path in our Makefiles. If
76 you see this, please email the LLVM bug mailing list with the name of
77 the offending Makefile and a description of what is wrong with it.
78
79 <dt><b>The <tt>configure</tt> script finds the right C compiler, but it
80 uses the LLVM linker from a previous build. What do I do?</b>
81 <dd>
82 The <tt>configure</tt> script uses the <tt>PATH</tt> to find
83 executables, so if it's grabbing the wrong linker/assembler/etc, there
84 are two ways to fix it:
85 <ol>
86 <li>Adjust your <tt>PATH</tt> environment variable so that the
87 correct program appears first in the <tt>PATH</tt>. This may work,
88 but may not be convenient when you want them <i>first</i> in your
89 path for other work.
90 <p>
91
92 <li>Run <tt>configure</tt> with an alternative <tt>PATH</tt> that
93 is correct. In a Borne compatible shell, the syntax would be:
94 <p>
95 <tt>PATH=<the path without the bad program> ./configure ...</tt>
96 <p>
97 This is still somewhat inconvenient, but it allows
98 <tt>configure</tt> to do its work without having to adjust your
99 <tt>PATH</tt> permanently.
100 </ol>
101
102 <dt><b>When creating a dynamic library, I get a strange GLIBC error.</b>
103 <dd>
104 Under some operating systems (i.e. Linux), libtool does not work correctly
105 if GCC was compiled with the --disable-shared option. To work around this,
106 install your own version of GCC that has shared libraries enabled by
107 default.
108 <p>
109
110 <dt><b>I've updated my source tree from CVS, and now my build is trying to
111 use a file/directory that doesn't exist.</b>
112 <dd>
113 You need to re-run configure in your object directory. When new Makefiles
114 are added to the source tree, they have to be copied over to the object
115 tree in order to be used by the build.
116 <p>
117
118 <dt><b>I've modified a Makefile in my source tree, but my build tree keeps
119 using the old version. What do I do?</b>
120 <dd>
121 If the Makefile already exists in your object tree, you can just run the
122 following command in the top level directory of your object tree:
123 <p>
124 <tt>./config.status &lt;relative path to Makefile&gt;</tt>
125 <p>
126 If the Makefile is new, you will have to modify the configure script to copy
127 it over.
128 <p>
129
130 <dt><b>I've upgraded to a new version of LLVM, and I get strange build
131 errors.</b>
132 <dd>
133 Sometimes changes to the LLVM source code alters how the build system
134 works. Changes in libtool, autoconf, or header file dependencies are
135 especially prone to this sort of problem.
136 <p>
137 The best thing to try is to remove the old files and re-build. In most
138 cases, this takes care of the problem. To do this, just type <tt>make
139 clean</tt> and then <tt>make</tt> in the directory that fails to build.
140 <p>
141</dl>
142<hr>
143
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