Hi again,<br><br>I can confirm r169783 fixes the problem. My testbench segfaulted in r169782 but works after your commit.<br><br>We can close the issue.<br><br>Thanks,<br><br>Carlos<br><div class="gmail_extra"><br><br><div class="gmail_quote">
2012/12/11 Carlos Sánchez de La Lama <span dir="ltr"><<a href="mailto:csanchezdll@gmail.com" target="_blank">csanchezdll@gmail.com</a>></span><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi Anshu,<br><br>I got a testbench which fails (and segfaults) consistently with an environment (gcc + os) conveniently preserved in a virtual machine. I will confirm that it is gone there and report.<br><br>Thanks for the fix :)<div class="HOEnZb">
<div class="h5"><br>
<br>Carlos<br><div class="gmail_extra"><br><br><div class="gmail_quote">2012/12/10 Anshuman Dasgupta <span dir="ltr"><<a href="mailto:adasgupt@codeaurora.org" target="_blank">adasgupt@codeaurora.org</a>></span><br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<div><tt>Carlos,</tt><tt><br>
</tt><tt><br>
</tt><tt>I committed a fix in r169783. Thanks for catching this.</tt><tt><br>
</tt><tt><br>
</tt><tt>However, I could not reproduce an invalid read or a
segfault even with fadd.ll. Is there a test case you can check
in that reproduces this bug? Even if the segfault occurs
intermittently, that's better than no test case at all.</tt><tt><br>
</tt><tt><br>
</tt><tt>Thanks</tt><div><tt><br>
</tt><tt>-Anshu</tt><tt><br>
</tt><tt><br>
</tt><tt>--- </tt><tt><br>
</tt><tt>Qualcomm Innovation Center, Inc. is a member of Code
Aurora Forum, hosted by The Linux Foundation </tt><tt><br>
<br>
</tt><tt><br>
</tt></div><div><div><tt>On 12/10/2012 1:01 PM, Carlos Sánchez de La Lama wrote:</tt><tt><br>
</tt></div></div></div><div><div>
<blockquote type="cite"><tt>Hi Anshu,</tt>
<div><tt><br>
</tt></div>
<div><tt>no, I did not fill a bug report. It is not so easy to
make the code fail noticeably; during Hexagon CodeGen tests it
happens silently and tests pass. I am working on another VLIW
backend which uses DFAPacketizer and compiling llvm with
gcc-4.4 makes it segfault, but with gcc-4.7 the bug gets
hidden again (it still happens, but values after
DFAStateEntryTable in memory are such that ReadTable does not
break bad).</tt></div>
<div><tt><br>
</tt></div>
<div><tt>If you find more info will help you track it down just
let me know :)</tt></div>
<div><tt><br>
</tt></div>
<div><tt>BR</tt></div>
<div><tt><br>
</tt></div>
<div><tt>Carlos</tt></div>
<div class="gmail_extra"><tt><br>
</tt><tt><br>
</tt>
<div class="gmail_quote"><tt>2012/12/10 Anshuman Dasgupta </tt><tt><span dir="ltr"><<a href="mailto:adasgupt@codeaurora.org" target="_blank">adasgupt@codeaurora.org</a>></span></tt><tt><br>
</tt>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<div><tt>Hi Carlos,</tt><tt><br>
</tt> <tt><br>
</tt> <tt>Thanks for identifying the bug. </tt><tt>I'll
confirm and fix.</tt><tt> Is there a bug report open
for this? </tt><tt><br>
</tt> <tt><br>
</tt> <tt>-Anshu</tt><tt><br>
</tt> <tt><br>
</tt> <tt>--- </tt><tt><br>
</tt> <tt>Qualcomm Innovation Center, Inc. is a member
of Code Aurora Forum, hosted by The Linux Foundation </tt><tt><br>
</tt>
<div>
<div> <tt><br>
</tt> <tt><br>
</tt> <tt><br>
</tt> <tt>On 12/10/2012 4:48 AM, Carlos Sánchez de
La Lama wrote:</tt><tt><br>
</tt> </div>
</div>
</div>
<blockquote type="cite">
<div>
<div><tt>Hi all,</tt><tt><br>
</tt> <tt><br>
</tt> <tt>I have found what I think it is a bug in
DFAPacketizer::ReadTable.</tt><tt><br>
</tt> <tt><br>
</tt> <tt>When finding NextStateInTable to cache
all transitions belonging to a state into
CachedTable, ReadTable does not check bounds:</tt><tt><br>
</tt> <tt><br>
</tt> <tt> unsigned ThisState =
DFAStateEntryTable[state];
|</tt><tt><br>
</tt> <tt>unsigned NextStateInTable =
DFAStateEntryTable[state+1]; </tt><tt><br>
</tt> <tt><br>
</tt> <tt>which makes NextStateInTable get a random
value when state == <last state in table>.
Behaviour changes depending on gcc version /
platform / ..., but in some cases might lead to
segmentation faults.</tt><tt><br>
</tt> <tt><br>
</tt> <tt>I have checked the problem happens in
Hexagon tests (for example fadd.ll test) but does
not break badly there (though CachedTable will get
some unneded and random data rows).</tt><tt><br>
</tt> <tt><br>
</tt> <tt>Probably making tblgen add an
end-of-table marker in
<Target>DFAStateEntryTable is the easiest
solution.</tt><tt><br>
</tt> <tt><br>
</tt> <tt>BR</tt><tt><br>
</tt> <tt><br>
</tt> <tt>Carlos</tt><tt><br>
</tt> <tt><br>
</tt>
<fieldset></fieldset>
<tt><br>
</tt> </div>
</div>
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