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<div class="moz-cite-prefix">On 28.03.2013 1:18, Anna Zaks wrote:<br>
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<div>On Mar 27, 2013, at 10:13 AM, Anton Yartsev <<a
moz-do-not-send="true" href="mailto:anton.yartsev@gmail.com">anton.yartsev@gmail.com</a>>
wrote:</div>
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<div class="moz-cite-prefix">On 27.03.2013 20:58, Anna Zaks
wrote:<br>
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<div>On Mar 26, 2013, at 6:10 PM, Anna Zaks <<a
moz-do-not-send="true" href="mailto:ganna@apple.com">ganna@apple.com</a>>
wrote:</div>
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On Mar 26, 2013, at 5:10 PM, Anton Yartsev <<a
moz-do-not-send="true"
href="mailto:anton.yartsev@gmail.com">anton.yartsev@gmail.com</a>>
wrote:</div>
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<div class="moz-cite-prefix">On 25.03.2013
21:39, Anna Zaks wrote:<br>
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<div>On Mar 25, 2013, at 9:30 AM, Jordan Rose
<<a moz-do-not-send="true"
href="mailto:jordan_rose@apple.com">jordan_rose@apple.com</a>>
wrote:</div>
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On Mar 25, 2013, at 8:01 , Anton Yartsev
<<a moz-do-not-send="true"
href="mailto:anton.yartsev@gmail.com">anton.yartsev@gmail.com</a>>
wrote:</div>
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<div class="moz-cite-prefix">Committed
as r177849</div>
<br>
Manage to find several random real
bugs (report-843813.html,
report-230257.html, recursive case in
report-727931.html), but for now it is
hard to detect real bugs among tons of
false-positives.<br>
<br>
There are two types of false-positives
that form the majority of reports:<br>
1) Illustrated by the following test
(added similar test to
NewDelete-checker-test.mm):<br>
int *global;<br>
void testMemIsOnHeap() {<br>
int *p = new int; // FIXME:
currently not heap allocated!<span
class="Apple-converted-space"> </span><br>
if (global != p) // evaluates to
UnknownVal() rather then 'true'<br>
global = p;<br>
} // report false-positive leak<br>
<br>
As I understand the problem is that
currently a memory region for 'new' is
not a heap region and this lead to
false-positives like
report-863595.html and others. (e.g.
that causes 'global != p' evaluate to
UnknownVal() rather then 'true' (logic
of SimpleSValBuilder::evalBinOpLL))<br>
<br>
Attached is the proposed patch that
fixes these issues. </div>
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<div>There are two reasons I didn't use
getConjuredHeapSymbol when I originally
put in this code:</div>
<div>(1) It handles all CXXNewExprs, even
if the allocator is not one of the
global ones.</div>
<div>(2) Heap symbols weren't used yet
(Anna added them later for
MallocChecker).</div>
<div><br>
</div>
<div>Obviously #2 is bogus now. #1 worries
me a bit because it requires duplicating
some of the checks you just added to
MallocChecker.</div>
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<div>In the long run, the design would be
to get the appropriate memory from the
allocator call, and we have PR12014's
restructuring of the CFG blocking that.
I'm not sure if we'd then move the heap
symbol logic into a checker, or if it
would still stay in Core.</div>
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</div>
<div>In the short term, I guess the best
idea is to duplicate some of the checks
(or refactor them to a helper function
somewhere...though probably<span
class="Apple-converted-space"> </span><i>not</i> into
AST) and then conjure a heap symbol if
we know we can.</div>
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Failed to find any suitable place other then AST
:) Eventually noticed, that actually only a
single check should be duplicated. Decided to
leave the wide comment added when I tried to
find the proper place for isStandardNewDelete().<br>
New fix attached.<br>
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<div text="#000000" bgcolor="#FFFFFF">2)
The second type of false-positives is
illustrated by the following minimal
test:<br>
void f(const int & x);<br>
<br>
void test() {<br>
int *p = (int *)malloc(sizeof(int));<br>
f(*p);<br>
} // report false-positive leak<br>
<br>
report-218274.html shows how it looks
like in reality.<br>
Haven't addressed this yet. Removing
'const' from the declaration
eliminates the leak report. </div>
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<div>Interesting. You can't change a const
region (and pedantically you can't
free() it either), but you certainly can
'delete' it. (C++11 [expr.delete]p2)</div>
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<div>Anna, any thoughts on this? Should
these also count as "pointer escaped"
even though their contents have not been
invalidated?</div>
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<div>I think handling this similarly to
pointer escape is the best. However, I am
concerned that if we simply extend pointer
escape to trigger on another "Kind" of
escape, all the other users of pointerEscape
will need to know about it (and do nothing
for this kind of escape). How about a new
checker callback, which will rely on the
same core code as _checkPointerEscape<span
style="font-family: Menlo;">? </span>This
way the checker developers would not need to
know about this special case, and we can
reuse all the code that determines when the
escape should be triggered.</div>
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As for me it would be better to leave the single
callback as this is just another type of pointer
escape, if I understand correctly. Have no other
arguments for this :)</div>
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<div text="#000000" bgcolor="#FFFFFF"
style="letter-spacing: normal; orphans: auto;
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widows: auto; word-spacing: 0px;
-webkit-text-size-adjust: auto;
-webkit-text-stroke-width: 0px;">In addition,
the "Kind" approach is relatively new, so
hopefully a few users of pointerEscape be
affected.<span class="Apple-converted-space"> </span><br>
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The main concern is that every user of the callback
will now have to check if the kind is ConstPointer
(or whatever we call it, maybe multiple kinds..) and
do nothing in that case. So every user will need to
know about this special case and handle it
specially.<br>
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<div>Anton,</div>
<div><br>
</div>
<div>If you don't mind, I am going to work on this one.
I have some spare time and we'd like to get the
new/delete checker out in the next open source build.<span
class="Apple-converted-space"> </span><br>
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I am OK with this, thanx!<br>
<br>
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Anton,</div>
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<div>I've realized that I need the part of your new/delete work
that tracks families for fixing this. Specifically, I want to
assume that a const pointer cannot be freed but could be
deleted. Can you commit the remaining patches? Specifically, I
need the part that performs family tracking, but you can commit
the mismatched deallocators work as well.</div>
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Committed at r178250<br>
<pre class="moz-signature" cols="72">--
Anton</pre>
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