mirror of
https://github.com/RPCS3/llvm-mirror.git
synced 2024-12-27 14:07:32 +00:00
271 lines
12 KiB
HTML
271 lines
12 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
|
|
<html><head><title>How to submit an LLVM bug report</title></head>
|
|
|
|
<body bgcolor=white>
|
|
|
|
<table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
|
|
<tr><td> <font size=+3 color="#EEEEFF" face="Georgia,Palatino,Times,Roman"><b>How to submit an LLVM bug report</b></font></td>
|
|
</tr></table>
|
|
|
|
<table border=0 width=100%>
|
|
<tr><td valign=top>
|
|
<p><font size=+1>
|
|
<ol>
|
|
<li><a href="#introduction">Introduction - Got bugs?</a>
|
|
<li><a href="#crashers">Crashing Bugs</a>
|
|
<ul>
|
|
<li><a href="#front-end">Front-end bugs</a>
|
|
<li><a href="#gccas">GCCAS bugs</a>
|
|
<li><a href="#gccld">GCCLD bugs</a>
|
|
<li><a href="#passes">Bugs in LLVM passes</a>
|
|
</ul>
|
|
<li><a href="#miscompilations">Miscompilations</a>
|
|
<li><a href="#codegen">Incorrect code generation (JIT and LLC)</a>
|
|
|
|
<p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
|
|
<a href="http://misha.brukman.net">Misha Brukman</a></b><p>
|
|
</ol><p></font>
|
|
</td><td valign=top align=right>
|
|
<img src="Debugging.gif" width=444 height=314>
|
|
</td></tr>
|
|
</table>
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
<table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
|
|
<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
|
|
<a name="introduction">Introduction - Got bugs?
|
|
</b></font></td></tr></table><ul>
|
|
<!-- *********************************************************************** -->
|
|
|
|
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>
|
|
|
|
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. 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>
|
|
|
|
Once you have a reduced test-case, email information about the bug to: <a
|
|
href="mailto:llvmbugs@cs.uiuc.edu">llvmbugs@cs.uiuc.edu</a>. This should
|
|
include all of the information necessary to reproduce the problem, including
|
|
where you got the LLVM tree from (if you're not working out of CVS).<p>
|
|
|
|
Thanks for helping us make LLVM better!<p>
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
|
|
<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
|
|
<a name="crashers">Crashing Bugs
|
|
</b></font></td></tr></table><ul>
|
|
<!-- *********************************************************************** -->
|
|
|
|
More often than not, bugs in the compiler cause it to crash - often due to an
|
|
assertion failure of some sort. If you are running <tt><b>opt</b></tt> or
|
|
<tt><b>analyze</b></tt> directly, and something crashes, jump to the section on
|
|
<a href="#passes">bugs in LLVM passes</a>. Otherwise, the most important
|
|
piece of the puzzle is to figure out if it is the GCC-based front-end that is
|
|
buggy or if it's one of the LLVM tools that has problems.<p>
|
|
|
|
To figure out which program is crashing (the front-end, <tt><b>gccas</b></tt>,
|
|
or <tt><b>gccld</b></tt>), run the <tt><b>llvm-gcc</b></tt> command line as you
|
|
were when the crash occurred, but add a <tt>-v</tt> option to the command line.
|
|
The compiler will print out a bunch of stuff, and should end with telling you
|
|
that one of <tt><b>cc1</b></tt>, <tt><b>gccas</b></tt>, or <tt><b>gccld</b></tt>
|
|
crashed.<p>
|
|
|
|
<ul>
|
|
<li>If <tt><b>cc1</b></tt> crashed, you found a problem with the front-end.
|
|
Jump ahead to the section on <a href="#front-end">front-end bugs</a>.
|
|
<li>If <tt><b>gccas</b></tt> crashed, you found a bug in <a href="#gccas">one of
|
|
the passes in <tt><b>gccas</b></tt></a>.
|
|
<li>If <tt><b>gccld</b></tt> crashed, you found a bug in <a href="#gccld">one
|
|
of the passes in <tt><b>gccld</b></tt></a>.
|
|
<li>Otherwise, something really weird happened. Email the list with what you
|
|
have at this point.
|
|
</ul><p>
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
|
|
<tr><td> </td><td width="100%">
|
|
<font color="#EEEEFF" face="Georgia,Palatino"><b>
|
|
<a name="front-end">Front-end bugs
|
|
</b></font></td></tr></table><ul>
|
|
|
|
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> (containing LLVM
|
|
assembly code), for each compiled <tt><i>foo</i>.c</tt> file. Send us
|
|
the <tt><i>foo</i>.i</tt> file, along with a brief description of the
|
|
error it caused.<p>
|
|
|
|
<!-- ======================================================================= -->
|
|
</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
|
|
<tr><td> </td><td width="100%">
|
|
<font color="#EEEEFF" face="Georgia,Palatino"><b>
|
|
<a name="gccas">GCCAS bugs
|
|
</b></font></td></tr></table><ul>
|
|
|
|
If you find that a bug crashes in the <tt><b>gccas</b></tt> stage of
|
|
compilation, compile your test-case to a <tt>.s</tt> file with the
|
|
<tt>-save-temps</tt> option to <tt><b>llvm-gcc</b></tt>. Then run:<p>
|
|
|
|
<pre>
|
|
<b>gccas</b> -debug-pass=Arguments < /dev/null -o - > /dev/null
|
|
</pre><p>
|
|
|
|
... which will print a list of arguments, indicating the list of passes that
|
|
<tt><b>gccas</b></tt> runs. Once you have the input file and the list of
|
|
passes, go to the section on <a href="#passes">debugging bugs in LLVM
|
|
passes</a>.<p>
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
|
|
<tr><td> </td><td width="100%">
|
|
<font color="#EEEEFF" face="Georgia,Palatino"><b>
|
|
<a name="gccld">GCCLD bugs
|
|
</b></font></td></tr></table><ul>
|
|
|
|
If you find that a bug crashes in the <tt><b>gccld</b></tt> stage of
|
|
compilation, gather all of the <tt>.o</tt> bytecode files and libraries that are
|
|
being linked together (the "<tt><b>llvm-gcc</b> -v</tt>" output should include
|
|
the full list of objects linked). Then run:<p>
|
|
|
|
<pre>
|
|
<b>llvm-as</b> < /dev/null > null.bc
|
|
<b>gccld</b> -debug-pass=Arguments null.bc
|
|
</pre><p>
|
|
|
|
... which will print a list of arguments, indicating the list of passes that
|
|
<tt><b>gccld</b></tt> runs. Once you have the input files and the list of
|
|
passes, go to the section on <a href="#passes">debugging bugs in LLVM
|
|
passes</a>.<p>
|
|
|
|
<!-- ======================================================================= -->
|
|
</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
|
|
<tr><td> </td><td width="100%">
|
|
<font color="#EEEEFF" face="Georgia,Palatino"><b>
|
|
<a name="passes">Bugs in LLVM passes
|
|
</b></font></td></tr></table><ul>
|
|
|
|
At this point, you should have some number of LLVM assembly files or bytecode
|
|
files and a list of passes which crash when run on the specified input. In
|
|
order to reduce the list of passes (which is probably large) and the input to
|
|
something tractable, use the <tt><b>bugpoint</b></tt> tool as follows:<p>
|
|
|
|
<pre>
|
|
<b>bugpoint</b> <input files> <list of passes>
|
|
</pre><p>
|
|
|
|
<tt><b>bugpoint</b></tt> will print a bunch of output as it reduces the
|
|
test-case, but it should eventually print something like this:<p>
|
|
|
|
<pre>
|
|
...
|
|
Emitted bytecode to 'bugpoint-reduced-simplified.bc'
|
|
|
|
*** You can reproduce the problem with: opt bugpoint-reduced-simplified.bc -licm
|
|
</pre><p>
|
|
|
|
Once you complete this, please send the LLVM bytecode file and the command line
|
|
to reproduce the problem to the llvmbugs mailing list.<p>
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
|
|
<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
|
|
<a name="miscompilations">Miscompilations</a>
|
|
</b></font></td></tr></table><ul>
|
|
<!-- *********************************************************************** -->
|
|
|
|
A miscompilation occurs when a pass does not correctly transform a program, thus
|
|
producing errors that are only noticed during execution. This is different from
|
|
producing invalid LLVM code (i.e., code not in SSA form, using values before
|
|
defining them, etc.) which the verifier will check for after a pass finishes its
|
|
run.<p>
|
|
|
|
To debug a miscompilation, you should choose which program you wish to run the
|
|
output through, e.g. C backend, the JIT, or LLC, and a selection of passes, one
|
|
of which may be causing the error, and run, for example:
|
|
|
|
<pre>
|
|
<b>bugpoint</b> -run-cbe -mode=compile [... optimization passes ...] file-to-test.bc
|
|
</pre>
|
|
|
|
<tt>bugpoint</tt> will try to narrow down your list of passes to the one pass
|
|
that causes an error, and simplify the bytecode file as much as it can to assist
|
|
you. It will print a message letting you know how to reproduce the resulting
|
|
error.
|
|
|
|
<!-- *********************************************************************** -->
|
|
</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
|
|
<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
|
|
<a name="codegen">Incorrect code generation</a>
|
|
</b></font></td></tr></table><ul>
|
|
<!-- *********************************************************************** -->
|
|
|
|
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>
|
|
|
|
To debug the JIT:
|
|
<pre>
|
|
<b>bugpoint</b> -run-jit -mode=codegen -output=[correct output file] [bytecodefile]
|
|
</pre>
|
|
|
|
Similarly, to debug the LLC, one would run:
|
|
<pre>
|
|
<b>bugpoint</b> -run-llc -mode=codegen -output=[correct output file] [bytecodefile]
|
|
</pre>
|
|
|
|
At the end of a successful <tt>bugpoint</tt> run, you will be presented
|
|
with two bytecode 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>
|
|
|
|
To reproduce the error that <tt>bugpoint</tt> found, it is sufficient to do the
|
|
following:
|
|
|
|
<ol>
|
|
<li>Regenerate the shared object from the safe bytecode file:<br>
|
|
<pre>
|
|
<b>llvm-dis</b> -c safe.bc -o safe.c<br>
|
|
<b>gcc</b> -shared safe.c -o safe.so
|
|
</pre></li>
|
|
<li>If debugging LLC, compile test bytecode native and link with the shared object:<br>
|
|
<pre>
|
|
<b>llc</b> test.bc -o test.s -f<br>
|
|
gcc test.s safe.so -o test.llc<br>
|
|
./test.llc [program options]
|
|
</pre></li>
|
|
<p>
|
|
If debugging the JIT, load the shared object and supply the test bytecode:<br>
|
|
<pre>
|
|
<b>lli</b> -load=safe.so test.bc [program options]
|
|
</pre></li>
|
|
</ol>
|
|
|
|
<!-- *********************************************************************** -->
|
|
</ul>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<hr><font size-1>
|
|
<address><a href="mailto:sabre@nondot.org">Chris Lattner</a></address>
|
|
<!-- Created: Tue Aug 6 15:00:33 CDT 2002 -->
|
|
<!-- hhmts start -->
|
|
Last modified: Wed Sep 17 13:49:15 CDT 2003
|
|
<!-- hhmts end -->
|
|
</font></body></html>
|