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5 <title>How to submit an LLVM bug report</title>
6 <link rel="stylesheet" href="llvm.css" type="text/css">
7</head>
8<body>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]9
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]10<div class="doc_title">
11 How to submit an LLVM bug report
12</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]13
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]14<table border="0" width="100%">
15<tr>
16<td valign="top">
17
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]18<ol>
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]19 <li><a href="#introduction">Introduction - Got bugs?</a></li>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]20 <li><a href="#crashers">Crashing Bugs</a>
21 <ul>
22 <li><a href="#front-end">Front-end bugs</a>
23 <li><a href="#gccas">GCCAS bugs</a>
24 <li><a href="#gccld">GCCLD bugs</a>
25 <li><a href="#passes">Bugs in LLVM passes</a>
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]26 </ul></li>
27 <li><a href="#miscompilations">Miscompilations</a></li>
28 <li><a href="#codegen">Incorrect code generation (JIT and LLC)</a></li>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]29
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]30</ol>
31
Misha Brukman637cab02004-01-15 19:03:47 +0000[diff] [blame]32<div class="doc_text">
33 <p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
34 <a href="http://misha.brukman.net">Misha Brukman</a></b></p>
35</div>
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]36
37</td>
38<td align="right">
Misha Brukman637cab02004-01-15 19:03:47 +0000[diff] [blame]39 <img src="Debugging.gif" alt="Debugging" width="444" height="314">
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]40</td>
41</tr>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]42</table>
43
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]44<!-- *********************************************************************** -->
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]45<div class="doc_section">
46 <a name="introduction">Introduction - Got bugs?</a>
47</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]48<!-- *********************************************************************** -->
49
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]50<div class="doc_text">
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]51
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]52<p>If you're working with LLVM and run into a bug, we definitely want to know
53about it. This document describes what you can do to increase the odds of
54getting it fixed quickly.</p>
55
56<p>Basically you have to do two things at a minimum. First, decide whether the
57bug <a href="#crashers">crashes the compiler</a> (or an LLVM pass), or if the
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]58compiler is <a href="#miscompilations">miscompiling</a> the program. Based on
59what type of bug it is, follow the instructions in the linked section to narrow
60down the bug so that the person who fixes it will be able to find the problem
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]61more easily.</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]62
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]63<p>Once you have a reduced test-case, go to <a
64href="http://llvm.cs.uiuc.edu/bugs/enter_bug.cgi">the LLVM Bug Tracking
65System</a>, select the category in which the bug falls, and fill out the form
66with the necessary details. The bug description should contain the following
67information:</p>
68
John Criswell4d37c7b2003-10-22 15:06:11 +0000[diff] [blame]69<ul>
Misha Brukmanafac73e2003-10-22 17:01:44 +0000[diff] [blame]70 <li>All information necessary to reproduce the problem.</li>
71 <li>The reduced test-case that triggers the bug.</li>
72 <li>The location where you obtained LLVM (if not from our CVS
73 repository).</li>
John Criswell4d37c7b2003-10-22 15:06:11 +0000[diff] [blame]74</ul>
75
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]76<p>Thanks for helping us make LLVM better!</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]77
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]78</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]79
80<!-- *********************************************************************** -->
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]81<div class="doc_section">
82 <a name="crashers">Crashing Bugs</a>
83</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]84<!-- *********************************************************************** -->
85
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]86<div class="doc_text">
87
88<p>More often than not, bugs in the compiler cause it to crash - often due to an
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]89assertion failure of some sort. If you are running <tt><b>opt</b></tt> or
90<tt><b>analyze</b></tt> directly, and something crashes, jump to the section on
91<a href="#passes">bugs in LLVM passes</a>. Otherwise, the most important
92piece of the puzzle is to figure out if it is the GCC-based front-end that is
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]93buggy or if it's one of the LLVM tools that has problems.</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]94
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]95<p>To figure out which program is crashing (the front-end,
96<tt><b>gccas</b></tt>, or <tt><b>gccld</b></tt>), run the
97<tt><b>llvm-gcc</b></tt> command line as you were when the crash occurred, but
98add a <tt>-v</tt> option to the command line. The compiler will print out a
99bunch of stuff, and should end with telling you that one of <tt><b>cc1</b></tt>,
100<tt><b>gccas</b></tt>, or <tt><b>gccld</b></tt> crashed.</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]101
102<ul>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]103
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]104 <li>If <tt><b>cc1</b></tt> crashed, you found a problem with the front-end.
105 Jump ahead to the section on <a href="#front-end">front-end bugs</a>.</li>
106
107 <li>If <tt><b>gccas</b></tt> crashed, you found a bug in <a href="#gccas">one
108 of the passes in <tt><b>gccas</b></tt></a>.</li>
109
110 <li>If <tt><b>gccld</b></tt> crashed, you found a bug in <a href="#gccld">one
111 of the passes in <tt><b>gccld</b></tt></a>.</li>
112
113 <li>Otherwise, something really weird happened. Email the list with what you
114 have at this point.</li>
115
116</ul>
117
118</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]119
120<!-- ======================================================================= -->
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]121<div class="doc_subsection">
122 <a name="front-end">Front-end bugs</a>
123</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]124
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]125<div class="doc_text">
126
127<p>If the problem is in the front-end, you should re-run the same
Brian Gaekeeefe9792003-05-23 21:03:50 +0000[diff] [blame]128<tt>llvm-gcc</tt> command that resulted in the crash, but add the
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]129<tt>-save-temps</tt> option. The compiler will crash again, but it will leave
130behind a <tt><i>foo</i>.i</tt> file (containing preprocessed C source code) and
131possibly <tt><i>foo</i>.s</tt> (containing LLVM assembly code), for each
132compiled <tt><i>foo</i>.c</tt> file. Send us the <tt><i>foo</i>.i</tt> file,
133along with a brief description of the error it caused.</p>
134
135</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]136
137<!-- ======================================================================= -->
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]138<div class="doc_subsection">
139 <a name="gccas">GCCAS bugs</a>
140</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]141
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]142<div class="doc_text">
143
144<p>If you find that a bug crashes in the <tt><b>gccas</b></tt> stage of
Brian Gaekeeefe9792003-05-23 21:03:50 +0000[diff] [blame]145compilation, compile your test-case to a <tt>.s</tt> file with the
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]146<tt>-save-temps</tt> option to <tt><b>llvm-gcc</b></tt>. Then run:</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]147
148<pre>
149 <b>gccas</b> -debug-pass=Arguments &lt; /dev/null -o - &gt; /dev/null
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]150</pre>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]151
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]152<p>... which will print a list of arguments, indicating the list of passes that
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]153<tt><b>gccas</b></tt> runs. Once you have the input file and the list of
154passes, go to the section on <a href="#passes">debugging bugs in LLVM
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]155passes</a>.</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]156
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]157</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]158
159<!-- ======================================================================= -->
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]160<div class="doc_subsection">
161 <a name="gccld">GCCLD bugs</a>
162</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]163
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]164<div class="doc_text">
165
166<p>If you find that a bug crashes in the <tt><b>gccld</b></tt> stage of
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]167compilation, gather all of the <tt>.o</tt> bytecode files and libraries that are
168being linked together (the "<tt><b>llvm-gcc</b> -v</tt>" output should include
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]169the full list of objects linked). Then run:</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]170
171<pre>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]172 <b>llvm-as</b> &lt; /dev/null &gt; null.bc
Chris Lattnerddaf5002003-05-23 14:49:32 +0000[diff] [blame]173 <b>gccld</b> -debug-pass=Arguments null.bc
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]174</pre><p>
175
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]176<p>... which will print a list of arguments, indicating the list of passes that
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]177<tt><b>gccld</b></tt> runs. Once you have the input files and the list of
178passes, go to the section on <a href="#passes">debugging bugs in LLVM
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]179passes</a>.</p>
180
181</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]182
183<!-- ======================================================================= -->
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]184<div class="doc_subsection">
185 <a name="passes">Bugs in LLVM passes</a>
186</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]187
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]188<div class="doc_text">
189
190<p>At this point, you should have some number of LLVM assembly files or bytecode
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]191files and a list of passes which crash when run on the specified input. In
192order to reduce the list of passes (which is probably large) and the input to
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]193something tractable, use the <tt><b>bugpoint</b></tt> tool as follows:</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]194
195<pre>
196 <b>bugpoint</b> &lt;input files&gt; &lt;list of passes&gt;
197</pre><p>
198
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]199<p><tt><b>bugpoint</b></tt> will print a bunch of output as it reduces the
200test-case, but it should eventually print something like this:</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]201
202<pre>
203 ...
204 Emitted bytecode to 'bugpoint-reduced-simplified.bc'
205
206 *** You can reproduce the problem with: opt bugpoint-reduced-simplified.bc -licm
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]207</pre>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]208
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]209<p>Once you complete this, please send the LLVM bytecode file and the command
210line to reproduce the problem to the llvmbugs mailing list.</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]211
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]212</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]213
214<!-- *********************************************************************** -->
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]215<div class="doc_section">
216 <a name="miscompilations">Miscompilations</a>
217</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]218<!-- *********************************************************************** -->
219
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]220<div class="doc_text">
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]221
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]222<p>A miscompilation occurs when a pass does not correctly transform a program,
223thus producing errors that are only noticed during execution. This is different
224from producing invalid LLVM code (i.e., code not in SSA form, using values
225before defining them, etc.) which the verifier will check for after a pass
226finishes its run.</p>
227
228<p>To debug a miscompilation, you should choose which program you wish to run
229the output through, e.g. C backend, the JIT, or LLC, and a selection of passes,
230one of which may be causing the error, and run, for example:</p>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]231
232<pre>
Chris Lattner18ab2b92003-10-14 20:58:07 +0000[diff] [blame]233 <b>bugpoint</b> -run-cbe [... optimization passes ...] file-to-test.bc
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]234</pre>
235
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]236<p><tt>bugpoint</tt> will try to narrow down your list of passes to the one pass
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]237that causes an error, and simplify the bytecode file as much as it can to assist
238you. It will print a message letting you know how to reproduce the resulting
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]239error.</p>
240
241</div>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]242
243<!-- *********************************************************************** -->
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]244<div class="doc_section">
245 <a name="codegen">Incorrect code generation</a>
246</div>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]247<!-- *********************************************************************** -->
248
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]249<div class="doc_text">
250
251<p>Similarly to debugging incorrect compilation by mis-behaving passes, you can
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]252debug incorrect code generation by either LLC or the JIT, using
253<tt>bugpoint</tt>. The process <tt>bugpoint</tt> follows in this case is to try
254to narrow the code down to a function that is miscompiled by one or the other
255method, but since for correctness, the entire program must be run,
256<tt>bugpoint</tt> will compile the code it deems to not be affected with the C
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]257Backend, and then link in the shared object it generates.</p>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]258
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]259<p>To debug the JIT:</p>
260
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]261<pre>
Chris Lattner18ab2b92003-10-14 20:58:07 +0000[diff] [blame]262 <b>bugpoint</b> -run-jit -output=[correct output file] [bytecodefile]
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]263</pre>
264
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]265<p>Similarly, to debug the LLC, one would run:</p>
266
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]267<pre>
Chris Lattner18ab2b92003-10-14 20:58:07 +0000[diff] [blame]268 <b>bugpoint</b> -run-llc -output=[correct output file] [bytecodefile]
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]269</pre>
270
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]271<p>At the end of a successful <tt>bugpoint</tt> run, you will be presented
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]272with two bytecode files: a <em>safe</em> file which can be compiled with the C
273backend and the <em>test</em> file which either LLC or the JIT
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]274mis-codegenerates, and thus causes the error.</p>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]275
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]276<p>To reproduce the error that <tt>bugpoint</tt> found, it is sufficient to do
277the following:</p>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]278
279<ol>
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]280
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]281 <li>Regenerate the shared object from the safe bytecode file:<br>
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]282
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]283<pre>
Chris Lattner036e6392004-02-14 01:07:17 +0000[diff] [blame^]284 <b>llc</b> -march=c safe.bc -o safe.c<br>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]285 <b>gcc</b> -shared safe.c -o safe.so
286</pre></li>
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]287
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]288 <li>If debugging LLC, compile test bytecode native and link with the shared object:<br>
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]289
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]290<pre>
291 <b>llc</b> test.bc -o test.s -f<br>
292 gcc test.s safe.so -o test.llc<br>
293 ./test.llc [program options]
294</pre></li>
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]295
Misha Brukman637cab02004-01-15 19:03:47 +0000[diff] [blame]296 <li>If debugging the JIT, load the shared object and supply the test
297bytecode:
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]298
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]299<pre>
300 <b>lli</b> -load=safe.so test.bc [program options]
301</pre></li>
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]302
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000[diff] [blame]303</ol>
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]304
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]305</div>
306
Chris Lattner8b6be362003-05-21 22:21:07 +0000[diff] [blame]307<!-- *********************************************************************** -->
Misha Brukman94082392003-10-31 18:37:20 +0000[diff] [blame]308<hr>
Misha Brukman637cab02004-01-15 19:03:47 +0000[diff] [blame]309<address>
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315 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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