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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>
<div><br>
</div>
<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>
<div><br>
</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>
<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>
<div><br>
</div>
<div>Anna, any thoughts on this? Should these also
count as "pointer escaped" even though their
contents have not been invalidated?</div>
<div><br>
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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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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. <br>
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I am OK with this, thanx!<br>
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Cheers,</div>
<div>Anna.</div>
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<br>
Evolved another issue, that I first thought to be
related to case 1), here is the minimal test:<br>
struct S {<br>
int **p;<br>
};<br>
void testOk(S &s) {<br>
new(s.p) (int*)(new int); // false-positive leak<br>
}<br>
void testLeak() {<br>
S s;<br>
new(s.p) (int*)(new int); // real leak<br>
}<br>
<br>
Haven't addressed these yet. The leak is reported for
cases of the form 'small_vector.push_back(new
Something)', where push_back() uses placement new to
store data.<br>
<br>
<pre class="moz-signature" cols="72">--
Anton</pre>
<span><FixForCase1.patch></span></div>
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<pre class="moz-signature" cols="72">--
Anton</pre>
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