mirror of
https://github.com/RPCS3/llvm-mirror.git
synced 2024-12-23 12:08:25 +00:00
349 lines
12 KiB
HTML
349 lines
12 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
|
|
"http://www.w3.org/TR/html4/strict.dtd">
|
|
<html>
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<title>How to submit an LLVM bug report</title>
|
|
<link rel="stylesheet" href="llvm.css" type="text/css">
|
|
</head>
|
|
<body>
|
|
|
|
<h1>
|
|
How to submit an LLVM bug report
|
|
</h1>
|
|
|
|
<table class="layout" style="width: 90%" >
|
|
<tr class="layout">
|
|
<td class="left">
|
|
<ol>
|
|
<li><a href="#introduction">Introduction - Got bugs?</a></li>
|
|
<li><a href="#crashers">Crashing Bugs</a>
|
|
<ul>
|
|
<li><a href="#front-end">Front-end bugs</a>
|
|
<li><a href="#ct_optimizer">Compile-time optimization bugs</a>
|
|
<li><a href="#ct_codegen">Code generator bugs</a>
|
|
</ul></li>
|
|
<li><a href="#miscompilations">Miscompilations</a></li>
|
|
<li><a href="#codegen">Incorrect code generation (JIT and LLC)</a></li>
|
|
</ol>
|
|
<div class="doc_author">
|
|
<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
|
|
<a href="http://misha.brukman.net">Misha Brukman</a></p>
|
|
</div>
|
|
</td>
|
|
<td class="right">
|
|
<img src="img/Debugging.gif" alt="Debugging" width="444" height="314">
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<h2>
|
|
<a name="introduction">Introduction - Got bugs?</a>
|
|
</h2>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div>
|
|
|
|
<p>If you're working with LLVM and run into a bug, we definitely want to know
|
|
about it. This document describes what you can do to increase the odds of
|
|
getting it fixed quickly.</p>
|
|
|
|
<p>Basically you have to do two things at a minimum. First, decide whether the
|
|
bug <a href="#crashers">crashes the compiler</a> (or an LLVM pass), or if the
|
|
compiler is <a href="#miscompilations">miscompiling</a> the program (i.e., the
|
|
compiler successfully produces an executable, but it doesn't run right). Based
|
|
on
|
|
what type of bug it is, follow the instructions in the linked section to narrow
|
|
down the bug so that the person who fixes it will be able to find the problem
|
|
more easily.</p>
|
|
|
|
<p>Once you have a reduced test-case, go to <a
|
|
href="http://llvm.org/bugs/enter_bug.cgi">the LLVM Bug Tracking
|
|
System</a> and fill out the form with the necessary details (note that you don't
|
|
need to pick a category, just use the "new-bugs" category if you're not sure).
|
|
The bug description should contain the following
|
|
information:</p>
|
|
|
|
<ul>
|
|
<li>All information necessary to reproduce the problem.</li>
|
|
<li>The reduced test-case that triggers the bug.</li>
|
|
<li>The location where you obtained LLVM (if not from our Subversion
|
|
repository).</li>
|
|
</ul>
|
|
|
|
<p>Thanks for helping us make LLVM better!</p>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<h2>
|
|
<a name="crashers">Crashing Bugs</a>
|
|
</h2>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div>
|
|
|
|
<p>More often than not, bugs in the compiler cause it to crash—often due
|
|
to an assertion failure of some sort. The most important
|
|
piece of the puzzle is to figure out if it is crashing in the GCC front-end
|
|
or if it is one of the LLVM libraries (e.g. the optimizer or code generator)
|
|
that has problems.</p>
|
|
|
|
<p>To figure out which component is crashing (the front-end,
|
|
optimizer or code generator), run the
|
|
<tt><b>llvm-gcc</b></tt> command line as you were when the crash occurred, but
|
|
with the following extra command line options:</p>
|
|
|
|
<ul>
|
|
<li><tt><b>-O0 -emit-llvm</b></tt>: If <tt>llvm-gcc</tt> still crashes when
|
|
passed these options (which disable the optimizer and code generator), then
|
|
the crash is in the front-end. Jump ahead to the section on <a
|
|
href="#front-end">front-end bugs</a>.</li>
|
|
|
|
<li><tt><b>-emit-llvm</b></tt>: If <tt>llvm-gcc</tt> crashes with this option
|
|
(which disables the code generator), you found an optimizer bug. Jump ahead
|
|
to <a href="#ct_optimizer"> compile-time optimization bugs</a>.</li>
|
|
|
|
<li>Otherwise, you have a code generator crash. Jump ahead to <a
|
|
href="#ct_codegen">code generator bugs</a>.</li>
|
|
|
|
</ul>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="front-end">Front-end bugs</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>If the problem is in the front-end, you should re-run the same
|
|
<tt>llvm-gcc</tt> command that resulted in the crash, but add the
|
|
<tt>-save-temps</tt> option. The compiler will crash again, but it will leave
|
|
behind a <tt><i>foo</i>.i</tt> file (containing preprocessed C source code) and
|
|
possibly <tt><i>foo</i>.s</tt> for each
|
|
compiled <tt><i>foo</i>.c</tt> file. Send us the <tt><i>foo</i>.i</tt> file,
|
|
along with the options you passed to llvm-gcc, and a brief description of the
|
|
error it caused.</p>
|
|
|
|
<p>The <a href="http://delta.tigris.org/">delta</a> tool helps to reduce the
|
|
preprocessed file down to the smallest amount of code that still replicates the
|
|
problem. You're encouraged to use delta to reduce the code to make the
|
|
developers' lives easier. <a
|
|
href="http://gcc.gnu.org/wiki/A_guide_to_testcase_reduction">This website</a>
|
|
has instructions on the best way to use delta.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="ct_optimizer">Compile-time optimization bugs</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>If you find that a bug crashes in the optimizer, compile your test-case to a
|
|
<tt>.bc</tt> file by passing "<tt><b>-emit-llvm -O0 -c -o foo.bc</b></tt>".
|
|
Then run:</p>
|
|
|
|
<div class="doc_code">
|
|
<p><tt><b>opt</b> -std-compile-opts -debug-pass=Arguments foo.bc
|
|
-disable-output</tt></p>
|
|
</div>
|
|
|
|
<p>This command should do two things: it should print out a list of passes, and
|
|
then it should crash in the same way as llvm-gcc. If it doesn't crash, please
|
|
follow the instructions for a <a href="#front-end">front-end bug</a>.</p>
|
|
|
|
<p>If this does crash, then you should be able to debug this with the following
|
|
bugpoint command:</p>
|
|
|
|
<div class="doc_code">
|
|
<p><tt><b>bugpoint</b> foo.bc <list of passes printed by
|
|
<b>opt</b>></tt></p>
|
|
</div>
|
|
|
|
<p>Please run this, then file a bug with the instructions and reduced .bc files
|
|
that bugpoint emits. If something goes wrong with bugpoint, please submit the
|
|
"foo.bc" file and the list of passes printed by <b>opt</b>.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="ct_codegen">Code generator bugs</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>If you find a bug that crashes llvm-gcc in the code generator, compile your
|
|
source file to a .bc file by passing "<tt><b>-emit-llvm -c -o foo.bc</b></tt>"
|
|
to llvm-gcc (in addition to the options you already pass). Once your have
|
|
foo.bc, one of the following commands should fail:</p>
|
|
|
|
<ol>
|
|
<li><tt><b>llc</b> foo.bc</tt></li>
|
|
<li><tt><b>llc</b> foo.bc -relocation-model=pic</tt></li>
|
|
<li><tt><b>llc</b> foo.bc -relocation-model=static</tt></li>
|
|
</ol>
|
|
|
|
<p>If none of these crash, please follow the instructions for a
|
|
<a href="#front-end">front-end bug</a>. If one of these do crash, you should
|
|
be able to reduce this with one of the following bugpoint command lines (use
|
|
the one corresponding to the command above that failed):</p>
|
|
|
|
<ol>
|
|
<li><tt><b>bugpoint</b> -run-llc foo.bc</tt></li>
|
|
<li><tt><b>bugpoint</b> -run-llc foo.bc --tool-args
|
|
-relocation-model=pic</tt></li>
|
|
<li><tt><b>bugpoint</b> -run-llc foo.bc --tool-args
|
|
-relocation-model=static</tt></li>
|
|
</ol>
|
|
|
|
<p>Please run this, then file a bug with the instructions and reduced .bc file
|
|
that bugpoint emits. If something goes wrong with bugpoint, please submit the
|
|
"foo.bc" file and the option that llc crashes with.</p>
|
|
|
|
</div>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<h2>
|
|
<a name="miscompilations">Miscompilations</a>
|
|
</h2>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div>
|
|
|
|
<p>If llvm-gcc successfully produces an executable, but that executable doesn't
|
|
run right, this is either a bug in the code or a bug in the
|
|
compiler. The first thing to check is to make sure it is not using undefined
|
|
behavior (e.g. reading a variable before it is defined). In particular, check
|
|
to see if the program <a href="http://valgrind.org/">valgrind</a>s clean,
|
|
passes purify, or some other memory checker tool. Many of the "LLVM bugs" that
|
|
we have chased down ended up being bugs in the program being compiled, not
|
|
LLVM.</p>
|
|
|
|
<p>Once you determine that the program itself is not buggy, you should choose
|
|
which code generator you wish to compile the program with (e.g. C backend, the
|
|
JIT, or LLC) and optionally a series of LLVM passes to run. For example:</p>
|
|
|
|
<div class="doc_code">
|
|
<p><tt>
|
|
<b>bugpoint</b> -run-cbe [... optzn passes ...] file-to-test.bc --args -- [program arguments]</tt></p>
|
|
</div>
|
|
|
|
<p><tt>bugpoint</tt> will try to narrow down your list of passes to the one pass
|
|
that causes an error, and simplify the bitcode file as much as it can to assist
|
|
you. It will print a message letting you know how to reproduce the resulting
|
|
error.</p>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<h2>
|
|
<a name="codegen">Incorrect code generation</a>
|
|
</h2>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div>
|
|
|
|
<p>Similarly to debugging incorrect compilation by mis-behaving passes, you can
|
|
debug incorrect code generation by either LLC or the JIT, using
|
|
<tt>bugpoint</tt>. The process <tt>bugpoint</tt> follows in this case is to try
|
|
to narrow the code down to a function that is miscompiled by one or the other
|
|
method, but since for correctness, the entire program must be run,
|
|
<tt>bugpoint</tt> will compile the code it deems to not be affected with the C
|
|
Backend, and then link in the shared object it generates.</p>
|
|
|
|
<p>To debug the JIT:</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
bugpoint -run-jit -output=[correct output file] [bitcode file] \
|
|
--tool-args -- [arguments to pass to lli] \
|
|
--args -- [program arguments]
|
|
</pre>
|
|
</div>
|
|
|
|
<p>Similarly, to debug the LLC, one would run:</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
bugpoint -run-llc -output=[correct output file] [bitcode file] \
|
|
--tool-args -- [arguments to pass to llc] \
|
|
--args -- [program arguments]
|
|
</pre>
|
|
</div>
|
|
|
|
<p><b>Special note:</b> if you are debugging MultiSource or SPEC tests that
|
|
already exist in the <tt>llvm/test</tt> hierarchy, there is an easier way to
|
|
debug the JIT, LLC, and CBE, using the pre-written Makefile targets, which
|
|
will pass the program options specified in the Makefiles:</p>
|
|
|
|
<div class="doc_code">
|
|
<p><tt>
|
|
cd llvm/test/../../program<br>
|
|
make bugpoint-jit
|
|
</tt></p>
|
|
</div>
|
|
|
|
<p>At the end of a successful <tt>bugpoint</tt> run, you will be presented
|
|
with two bitcode files: a <em>safe</em> file which can be compiled with the C
|
|
backend and the <em>test</em> file which either LLC or the JIT
|
|
mis-codegenerates, and thus causes the error.</p>
|
|
|
|
<p>To reproduce the error that <tt>bugpoint</tt> found, it is sufficient to do
|
|
the following:</p>
|
|
|
|
<ol>
|
|
|
|
<li><p>Regenerate the shared object from the safe bitcode file:</p>
|
|
|
|
<div class="doc_code">
|
|
<p><tt>
|
|
<b>llc</b> -march=c safe.bc -o safe.c<br>
|
|
<b>gcc</b> -shared safe.c -o safe.so
|
|
</tt></p>
|
|
</div></li>
|
|
|
|
<li><p>If debugging LLC, compile test bitcode native and link with the shared
|
|
object:</p>
|
|
|
|
<div class="doc_code">
|
|
<p><tt>
|
|
<b>llc</b> test.bc -o test.s<br>
|
|
<b>gcc</b> test.s safe.so -o test.llc<br>
|
|
./test.llc [program options]
|
|
</tt></p>
|
|
</div></li>
|
|
|
|
<li><p>If debugging the JIT, load the shared object and supply the test
|
|
bitcode:</p>
|
|
|
|
<div class="doc_code">
|
|
<p><tt><b>lli</b> -load=safe.so test.bc [program options]</tt></p>
|
|
</div></li>
|
|
|
|
</ol>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<hr>
|
|
<address>
|
|
<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
|
|
src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
|
|
<a href="http://validator.w3.org/check/referer"><img
|
|
src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
|
|
|
|
<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
|
|
<a href="http://llvm.org/">The LLVM Compiler Infrastructure</a>
|
|
<br>
|
|
Last modified: $Date$
|
|
</address>
|
|
|
|
</body>
|
|
</html>
|