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There's no reason to "handle" unknown/undefined values in
evalBinOp() family of methods. The only thing you need to do is to
avoid producing unknown values in the first place, so that you
didn't need to perform calculations over them in evalBinOp(). The
earlier you eliminate the Unknown, the more accurate information
you'll be able to provide to the solver.<br>
<br>
Undefined values are values that result from undefined behavior
according to the language standard. You don't need to handle
Undefined values because there's a checker that'll interrupt the
analysis whenever the code tries to perform arithmetic on undefined
values, so your new handling code will never be executed in
practice.<br>
<br>
Unknown values represent values of expressions that the analyzer
doesn't know how to compute. You don't need to handle Unknown values
because instead you can always prevent them from appearing by fixing
the part of the analyzer that produces them - just teach the
analyzer how to compute them instead. Just get rid of them and you
won't need to handle them. If getting rid of a particular source of
Unknowns is suddenly hard (i.e. because certain semantics of the
language are hard to model), as a fallback you can still replace the
Unknown with a conjured symbol at that source of Unknowns.<br>
<br>
Additionally, there are already multiple unsystematic places in the
analyzer where we "symbolicate" Unknowns, such as
ExprEngine::VisitBinaryOperator:<br>
<br>
67 if (RightV.isUnknown()) {<br>
68 unsigned Count = currBldrCtx->blockCount();<br>
69 RightV = svalBuilder.conjureSymbolVal(nullptr,
B->getRHS(), LCtx,<br>
70 Count);<br>
71 }<br>
<br>
Which is, again, merely a workaround for producing unknowns in the
first place, and the proper fix is to avoid producing them. <br>
<br>
<div class="moz-cite-prefix">On 6/26/18 3:17 PM, Mikhail Ramalho
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAORA-9YKwO3g8R-uVoFipsVs7UaGLQXTFKmqdVA4YxuTpC-e1Q@mail.gmail.com">
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<div
style="text-decoration-style:initial;text-decoration-color:initial">Investigated
the constraint being dropped and found that it's because of
the pre-conditions enforced by evalBinOp. </div>
<div
style="text-decoration-style:initial;text-decoration-color:initial"><br>
</div>
<div
style="text-decoration-style:initial;text-decoration-color:initial">If
any of the arguments is unknown or undefined, the constraint
is dropped as the code only handles Loc/NonLoc types. I had
two ideas about that:</div>
<div
style="text-decoration-style:initial;text-decoration-color:initial"><br>
</div>
<div
style="text-decoration-style:initial;text-decoration-color:initial">-
Change evalBinOpLL, evalBinOpNN and evalBinOpLN to take SVals
are arguments (and obviously change the names): The good thing
is that the solution would be handled in the same place BUT
these methods are already quite big, and handling
unknown/undef would just make them bigger.</div>
<div
style="text-decoration-style:initial;text-decoration-color:initial"><br>
</div>
<div
style="text-decoration-style:initial;text-decoration-color:initial">-
Create new <span
style="background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">evalBinOpLU, <span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">evalBinOpNU, <span
style="background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">evalBinOpUL, evalBinOpUN
in the SValBuilder and implement them in
SimpleSValBuilder: it would make the code more modular
and easier to understand, but will require some
refactoring or <span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">evalBinOpLL, evalBinOpNN
and evalBinOpLN<span> will end up with duplicated
code.</span></span></span></span></span></div>
<div
style="text-decoration-style:initial;text-decoration-color:initial"><span
style="background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span><br>
</span></span></span></span></span></div>
<div
style="text-decoration-style:initial;text-decoration-color:initial"><span
style="background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span>Any
other suggestion?</span></span></span></span></span></div>
<div
style="text-decoration-style:initial;text-decoration-color:initial"><span
style="background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span><br>
</span></span></span></span></span></div>
<div
style="text-decoration-style:initial;text-decoration-color:initial"><span
style="background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span>Also,
a couple of questions:</span></span></span></span></span></div>
<div
style="text-decoration-style:initial;text-decoration-color:initial"><span
style="background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span><br>
</span></span></span></span></span></div>
<div
style="text-decoration-style:initial;text-decoration-color:initial">1.
What's the difference between a unknown and a undefined symbol
when analyzing a program?</div>
<div
style="text-decoration-style:initial;text-decoration-color:initial"><br>
</div>
<div
style="text-decoration-style:initial;text-decoration-color:initial">From
what I understood, an unknown symbol is the same as "I don't
understand this expression" or arguments that we don't its
value and undefined is, well, undefined values (e.g.,
uninitialized variables). But when building constraints, does
it make any difference? I mean, from an SMT point of view,
they would be the same, free variables.</div>
<div
style="text-decoration-style:initial;text-decoration-color:initial"><br>
</div>
<div
style="text-decoration-style:initial;text-decoration-color:initial">Thank
you,</div>
<br>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr">Em ter, 26 de jun de 2018 às 19:54, Artem
Dergachev <<a href="mailto:noqnoqneo@gmail.com"
moz-do-not-send="true">noqnoqneo@gmail.com</a>> escreveu:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">I believe
that even if the constraint manager can't "handle" constraints
<br>
on a symbol, symbols should still be emitted. Because "can
handle" here <br>
means "can simplify the symbol properly", not "can track
constraints <br>
over the symbol". The constraint manager would still at least
be able to <br>
handle the symbol as an opaque symbol and track constraints
over it.<br>
<br>
In other words, it's still beneficial to know that "(a % b) ==
0" even <br>
if we've no idea what "%" means, because when we see "(a % b)"
next <br>
time, even if we've still no idea what it means, we'll know
that it's <br>
zero anyway.<br>
<br>
<br>
On 6/26/18 10:49 AM, Dominic Chen via cfe-dev wrote:<br>
> Another solution, since you're using Z3 already, is to
implement runtime<br>
> support for querying the underlying ConstraintManager's
about the types<br>
> of constraints that it supports (e.g. canReasonAboutFoo()
). Then, you<br>
> can use this to generate the appropriate SVal's at
runtime, which could<br>
> include support for symbolic extension/truncation,
remainder, shifts, etc.<br>
><br>
> I have two stale patches that implement this, D28955 and
D35450. The<br>
> first might solve your problem with remainders; see the
changes to<br>
> SimpleSValBuilder.<br>
><br>
> Dominic<br>
><br>
> On 6/26/2018 1:23 PM, Mikhail Ramalho via cfe-dev wrote:<br>
>> Hi all,<br>
>><br>
>> Hi guys,<br>
>><br>
>> I'm investigating the constraints being dropped,
here's what I got so far.<br>
>><br>
>> First of all, I'm using the following program:<br>
>><br>
>> void foo(unsigned width)<br>
>> {<br>
>> int base;<br>
>> int i = 0;<br>
>><br>
>> if (!(i % width))<br>
>> base = 1;<br>
>><br>
>> if(base == 1)<br>
>> abort();<br>
>> }<br>
>><br>
>> I started by looking at ExprEngine::processBranch,
where<br>
>><br>
>> SVal X = PrevState->getSVal(Condition,
PredI->getLocationContext());<br>
>><br>
>> returns Unknown for the remainder condition. The
getSVal ends up<br>
>> looking in a map for the value result, so I found
that bindExpr fills<br>
>> that map.<br>
>><br>
>> Going back a bit, into ExprEngine::Visit, when
evaluating a<br>
>> Stmt::BinaryOperatorClass (regardless of the eagerly
assume flag)<br>
>> ExprEngine::VisitBinaryOperator is called, which
eventually calls<br>
>> evalBinOp and, since it doesn't understand remainder,
it returns<br>
>> unknown and BindExpr is never called.<br>
>><br>
>> Back to ExprEngine::processBranch, when the symbol is
unknown the<br>
>> following piece of code is called:<br>
>><br>
>> // If the condition is still unknown, give up.<br>
>> if (X.isUnknownOrUndef()) {<br>
>> builder.generateNode(PrevState, true, PredI);<br>
>> builder.generateNode(PrevState, false, PredI);<br>
>> continue;<br>
>> }<br>
>><br>
>> and the condition is simply ignored. When the result
is defined, it<br>
>> creates two nodes assuming the constraints.<br>
>><br>
>> ~<br>
>><br>
>> My idea is when the SVal is undef or unknown, instead
of generating<br>
>> two nodes with no knowledge about the constraints,
we could create<br>
>> two ranged constraints, like:<br>
>><br>
>> i % width: [0,0]<br>
>><br>
>> and<br>
>><br>
>> i % width: [1,1]<br>
>><br>
>> for each path. That way we can keep the constraints
with reasonable<br>
>> values.<br>
>><br>
>> What do you think? It feels like this will break
stuff further down<br>
>> the line, but I'll know for sure if I implement the
change.<br>
>><br>
>> ~<br>
>><br>
>> Artem's response:<br>
>><br>
>> Yep, i strongly believe that any UnknownVal should be
treated as a<br>
>> synonym of "not implemented".<br>
>><br>
>> In *this* example you might also notice that there's
no symbol for 'i',<br>
>> but it's a concrete integer 0 instead. So you can
evaluate the whole<br>
>> remainder to 0, unless 'width' is also equal to 0 (in
which case the<br>
>> answer would be UndefinedVal). Also note that when
enabled, DivZero<br>
>> checker will refute the 'width == 0' branch.<br>
>><br>
>> In the general case you have no choice but to produce
an IntSymExpr (if<br>
>> 'i' is a concrete integer other than 0) or a
SymSymExpr (if 'i' is a<br>
>> symbol).<br>
>><br>
>><br>
>> Em qui, 24 de mai de 2018 às 18:15, Mikhail Ramalho<br>
>> <<a href="mailto:mikhail.ramalho@gmail.com"
target="_blank" moz-do-not-send="true">mikhail.ramalho@gmail.com</a>
<mailto:<a href="mailto:mikhail.ramalho@gmail.com"
target="_blank" moz-do-not-send="true">mikhail.ramalho@gmail.com</a>>>
escreveu:<br>
>><br>
>><br>
>> Total Time time.analyzer.time.sys
(s) (mean)<br>
>> time.analyzer.time.user (s) (mean)
time.analyzer.time.wall (s)<br>
>> (mean) <br>
>> <br>
>> Reported bugs<br>
>> Tmux 99.2 0.076 27.253 7.656 <br>
>> <br>
>> 32<br>
>> Tmux + z3 152.88 0.074 56.251 11.505
<br>
>> <br>
>> 32<br>
>> Ratio 154.11% 97.37% 206.40%
150.27% <br>
>> Diff 0<br>
>><br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> Redis 173.69 0.057 7.083 7.271 <br>
>> <br>
>> 146<br>
>> Redis + z3 193.43 0.057 7.621 7.728 <br>
>> <br>
>> 140<br>
>> Ratio 111.37% 100.00% 107.60%
106.29% <br>
>> Diff 6<br>
>><br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> OpenSSL 264.93 0.042 3.31 3.412 <br>
>> <br>
>> 204<br>
>> OpenSSL + z3 213.53 0.035 3.099 3.152 <br>
>> <br>
>> 204<br>
>> Ratio 80.60% 83.33% 93.63% 92.38% <br>
>> Diff 0<br>
>><br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> Twin 143.17 0.067 6.593 6.696 <br>
>> <br>
>> 138<br>
>> Twin + z3 133.83 0.06 6.79 6.882 <br>
>> <br>
>> 138<br>
>> Ratio 93.48% 89.55% 102.99% 102.78%
<br>
>> Diff 0<br>
>><br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> Git + z3 333.9 0.075 8.52 8.67
<br>
>> <br>
>> 96<br>
>> Git + z3 289.59 0.062 7.924 8.023 <br>
>> <br>
>> 90<br>
>> Ratio 86.73% 82.67% 93.00% 92.54% <br>
>> Diff 6<br>
>><br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> Postgresql 889.35 0.079 8.482 8.631 <br>
>> <br>
>> 676<br>
>> Postgresql + z3 902.86 0.077 9.694
9.863 <br>
>> <br>
>> 676<br>
>> Ratio 101.52% 97.47% 114.29%
114.27% <br>
>> Diff 0<br>
>><br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> Sqlite3 1206.3 0.262 368.446
370.786 <br>
>> <br>
>> 200<br>
>> Sqlite3 + z3 1260.85 0.43 407.763
409.688 <br>
>> <br>
>> 199<br>
>> Ratio 104.52% 164.12% 110.67%
110.49% <br>
>> Diff 1<br>
>><br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>><br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> <br>
>> Average 104.62% 102.07%
118.37% 109.86% <br>
>> <br>
>> <br>
>><br>
>><br>
>><br>
>> 2018-05-24 15:11 GMT+01:00 Mikhail Ramalho<br>
>> <<a href="mailto:mikhail.ramalho@gmail.com"
target="_blank" moz-do-not-send="true">mikhail.ramalho@gmail.com</a>
<mailto:<a href="mailto:mikhail.ramalho@gmail.com"
target="_blank" moz-do-not-send="true">mikhail.ramalho@gmail.com</a>>>:<br>
>><br>
>> Hi all,<br>
>><br>
>> This is my first report to the community,
comparing the<br>
>> results with and without the Z3 refutation
when analyzing a<br>
>> number of projects.<br>
>><br>
>> ~<br>
>><br>
>> First of all, I'd like to thank Réka Kovács
as the first<br>
>> version of the refutation using Z3 was
created by her<br>
>> (<a href="https://reviews.llvm.org/D45517"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://reviews.llvm.org/D45517</a>)!
Thank you very much!<br>
>><br>
>> After applying patch D45517, you can use the
refutation check<br>
>> by using -analyzer-config
crosscheck-with-z3=true. Obviously,<br>
>> you need a version of clang built with Z3.<br>
>><br>
>> ~<br>
>><br>
>> I'm currently analyzing 7 C projects
(unfortunately, there's a<br>
>> bug preventing us from analyzing FFmpeg):<br>
>><br>
>> 1. Tmux<br>
>> 2. Redis<br>
>> 3. OpenSSL<br>
>> 4. Twin<br>
>> 5. Git<br>
>> 6. Postgresql<br>
>> 7. Sqlite3<br>
>><br>
>> In short, the refutation check slows down
the verification by<br>
>> ~20%. It removed 6 FPs from Redis, 6 FPs
from git and 1 FP<br>
>> from Sqlite3 (FP means false positive).
Surprisingly enough,<br>
>> some analysis were faster with the
crosscheck, but I'm not<br>
>> sure why (maybe ccache?).<br>
>><br>
>> Attached is a spreadsheet (report1.ods) with
some number<br>
>> (total time, average time per check, # of
reported bugs) and a<br>
>> txt with all the raw data from the analysis
(raw.txt). I'll<br>
>> add these data to google drive for the next
report.<br>
>><br>
>> In order to generate the raw data, you need
to use a version<br>
>> of clang with assertions enabled, call
scan-build.py with<br>
>> '-analyzer-config serialize-stats=true' and
you need to apply<br>
>> patch <a
href="https://reviews.llvm.org/D43134" rel="noreferrer"
target="_blank" moz-do-not-send="true">https://reviews.llvm.org/D43134</a>.<br>
>><br>
>> Thank you very much,<br>
>><br>
>><br>
>> 2018-05-01 15:27 GMT+01:00 Mikhail Ramalho<br>
>> <<a
href="mailto:mikhail.ramalho@gmail.com" target="_blank"
moz-do-not-send="true">mikhail.ramalho@gmail.com</a>
<mailto:<a href="mailto:mikhail.ramalho@gmail.com"
target="_blank" moz-do-not-send="true">mikhail.ramalho@gmail.com</a>>>:<br>
>><br>
>> Hello all,<br>
>><br>
>> My proposal for GSoC 2018 [0] about Bug
Validation in the<br>
>> Clang Static Analyzer using the Z3 SMT
Solver was accepted.<br>
>><br>
>> I'll work with George Karpenkov to
improve the bug reports<br>
>> that the static analyzer produces by
reducing the number<br>
>> of false bugs.<br>
>><br>
>> Thank you,<br>
>><br>
>> [0] <a
href="https://docs.google.com/document/d/1-zNSv0l4WyoxYpJUAw8LFnQq_TY4AGjIpPu1VPkmO-g"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://docs.google.com/document/d/1-zNSv0l4WyoxYpJUAw8LFnQq_TY4AGjIpPu1VPkmO-g</a><br>
>><br>
>> --<br>
>><br>
>> Mikhail Ramalho.<br>
>><br>
>><br>
>><br>
>><br>
>> --<br>
>><br>
>> Mikhail Ramalho.<br>
>><br>
>><br>
>><br>
>><br>
>> --<br>
>><br>
>> Mikhail Ramalho.<br>
>><br>
>><br>
>><br>
>> -- <br>
>><br>
>> Mikhail Ramalho.<br>
>><br>
>><br>
>> _______________________________________________<br>
>> cfe-dev mailing list<br>
>> <a href="mailto:cfe-dev@lists.llvm.org"
target="_blank" moz-do-not-send="true">cfe-dev@lists.llvm.org</a><br>
>> <a
href="http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev"
rel="noreferrer" target="_blank" moz-do-not-send="true">http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev</a><br>
><br>
> _______________________________________________<br>
> cfe-dev mailing list<br>
> <a href="mailto:cfe-dev@lists.llvm.org" target="_blank"
moz-do-not-send="true">cfe-dev@lists.llvm.org</a><br>
> <a
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<br>
</blockquote>
</div>
<br clear="all">
<div><br>
</div>
-- <br>
<div dir="ltr" class="gmail_signature"
data-smartmail="gmail_signature">
<div dir="ltr">
<div><br>
</div>
<div>Mikhail Ramalho.</div>
</div>
</div>
</blockquote>
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