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<div>Hi everyone,</div>
<div><br>
</div>
<div>The clang static analyzer gives a false positive warning on the following program:</div>
<div><br>
</div>
<div style="font-family: -webkit-standard;">
<blockquote style="margin: 0px 0px 0px 40px; border: none; padding: 0px;">
<div><font face="Consolas" style="font-size: 14px;">$ cat falseLeak.cpp </font></div>
<div><font face="Consolas" style="font-size: 14px;">struct CtrlBlk {</font></div>
<div><font face="Consolas" style="font-size: 14px;"> explicit CtrlBlk() : m_useCount(1) {}</font></div>
<div><font face="Consolas" style="font-size: 14px;"><br>
</font></div>
<div><font face="Consolas" style="font-size: 14px;"> virtual void dispose();</font></div>
<div><font face="Consolas" style="font-size: 14px;"><br>
</font></div>
<div><font face="Consolas" style="font-size: 14px;"> void decUseCount() {</font></div>
<div><font face="Consolas" style="font-size: 14px;"> -- m_useCount;</font></div>
<div><font face="Consolas" style="font-size: 14px;"> if (m_useCount == 0) { dispose(); }</font></div>
<div><font face="Consolas" style="font-size: 14px;"> }</font></div>
<div><font face="Consolas" style="font-size: 14px;"><br>
</font></div>
<div><font face="Consolas" style="font-size: 14px;"> int m_useCount;</font></div>
<div><font face="Consolas" style="font-size: 14px;">};</font></div>
<div><font face="Consolas" style="font-size: 14px;"><br>
</font></div>
<div><font face="Consolas" style="font-size: 14px;">struct Ptr {</font></div>
<div><font face="Consolas" style="font-size: 14px;"> Ptr() { m_cntrlBlk = new CtrlBlk; }</font></div>
<div><font face="Consolas" style="font-size: 14px;"> ~Ptr() { m_cntrlBlk->decUseCount(); }</font></div>
<div><font face="Consolas" style="font-size: 14px;"> CtrlBlk* m_cntrlBlk;</font></div>
<div><font face="Consolas" style="font-size: 14px;">};</font></div>
<div><font face="Consolas" style="font-size: 14px;"><br>
</font></div>
<div><font face="Consolas" style="font-size: 14px;">void testCase() { Ptr px; }</font></div>
<div><font face="Consolas" style="font-size: 14px;"><br>
</font></div>
<div><font face="Consolas" style="font-size: 14px;"><br>
</font></div>
<div><font face="Consolas" style="font-size: 14px;">$ clang-tidy -checks=* falseLeak.cpp </font></div>
<div><font face="Consolas" style="font-size: 14px;">1 warning generated.</font></div>
<div><font face="Consolas" style="font-size: 14px;">/Users/benoit/tmp/falseLeak.cpp:20:27: warning: Potential leak of memory pointed to by 'px.m_cntrlBlk' [clang-analyzer-cplusplus.NewDeleteLeaks]</font></div>
<div><font face="Consolas" style="font-size: 14px;">void testCase() { Ptr px; }</font></div>
<div><font face="Consolas" style="font-size: 14px;"> ^</font></div>
<div><font face="Consolas" style="font-size: 14px;">/Users/benoit/tmp/falseLeak.cpp:20:23: note: Calling default constructor for 'Ptr'</font></div>
<div><font face="Consolas" style="font-size: 14px;">void testCase() { Ptr px; }</font></div>
<div><font face="Consolas" style="font-size: 14px;"> ^</font></div>
<div><font face="Consolas" style="font-size: 14px;">/Users/benoit/tmp/falseLeak.cpp:15:26: note: Memory is allocated</font></div>
<div><font face="Consolas" style="font-size: 14px;"> Ptr() { m_cntrlBlk = new CtrlBlk; }</font></div>
<div><font face="Consolas" style="font-size: 14px;"> ^</font></div>
<div><font face="Consolas" style="font-size: 14px;">/Users/benoit/tmp/falseLeak.cpp:20:23: note: Returning from default constructor for 'Ptr'</font></div>
<div><font face="Consolas" style="font-size: 14px;">void testCase() { Ptr px; }</font></div>
<div><font face="Consolas" style="font-size: 14px;"> ^</font></div>
<div><font face="Consolas" style="font-size: 14px;">/Users/benoit/tmp/falseLeak.cpp:20:27: note: Potential leak of memory pointed to by 'px.m_cntrlBlk'</font></div>
<div><font face="Consolas" style="font-size: 14px;">void testCase() { Ptr px; }</font></div>
<div><font face="Consolas" style="font-size: 14px;"> ^</font></div>
</blockquote>
<div style="font-family: Calibri, sans-serif;"><br>
</div>
</div>
<div>Here’s my solution to silence up that false positive:</div>
<div><br>
</div>
<div style="font-family: -webkit-standard;">
<blockquote style="margin: 0px 0px 0px 40px; border: none; padding: 0px;">
<div><font face="Consolas" style="font-size: 14px;">#ifdef __clang_analyzer__</font></div>
<div><font face="Consolas" style="font-size: 14px;"> /// \brief Escape a variable from the analysis of the clang static analyzer</font></div>
<div><font face="Consolas" style="font-size: 14px;"> ///</font></div>
<div><font face="Consolas" style="font-size: 14px;"> /// This function takes a reference to a variable as an argument. This</font></div>
<div><font face="Consolas" style="font-size: 14px;"> /// causes the static analyzer tool to notice that the variable has escape</font></div>
<div><font face="Consolas" style="font-size: 14px;"> /// the scope of its analysis. It forces the static analyzer to make very</font></div>
<div><font face="Consolas" style="font-size: 14px;"> /// conservative assumptions about the state of the variable. This also</font></div>
<div><font face="Consolas" style="font-size: 14px;"> /// includes assumptions about any memory location referenced by this</font></div>
<div><font face="Consolas" style="font-size: 14px;"> /// variable.</font></div>
<div><font face="Consolas" style="font-size: 14px;"> ///</font></div>
<div><font face="Consolas" style="font-size: 14px;"> /// This can be used to silence up false positives. In general, it is</font></div>
<div><font face="Consolas" style="font-size: 14px;"> /// better to augment the information available to the static analyzer</font></div>
<div><font face="Consolas" style="font-size: 14px;"> /// using attributes and/or assertions. Unfortunately, this isn't always</font></div>
<div><font face="Consolas" style="font-size: 14px;"> /// possible. For example, it might be impossible to describe that a given</font></div>
<div><font face="Consolas" style="font-size: 14px;"> /// object is destructed along all execution paths.</font></div>
<div><font face="Consolas" style="font-size: 14px;"> template <typename V> static void escapeFromClangStaticAnalysis(V& escapedVar);</font></div>
<div><font face="Consolas" style="font-size: 14px;">#endif</font></div>
<div><font face="Consolas" style="font-size: 14px;"><br>
</font></div>
<div><font face="Consolas" style="font-size: 14px;">struct CtrlBlk {</font></div>
<div><font face="Consolas" style="font-size: 14px;"> explicit CtrlBlk() : m_useCount(1) {}</font></div>
<div><font face="Consolas" style="font-size: 14px;"><br>
</font></div>
<div><font face="Consolas" style="font-size: 14px;"> virtual void dispose();</font></div>
<div><font face="Consolas" style="font-size: 14px;"><br>
</font></div>
<div><font face="Consolas" style="font-size: 14px;"> void decUseCount() {</font></div>
<div><font face="Consolas" style="font-size: 14px;"> -- m_useCount;</font></div>
<div><font face="Consolas" style="font-size: 14px;"> if (m_useCount == 0) { dispose(); }</font></div>
<div><font face="Consolas" style="font-size: 14px;">#ifdef __clang_analyzer__</font></div>
<div><font face="Consolas" style="font-size: 14px;"> escapeFromClangStaticAnalysis(m_useCount);</font></div>
<div><font face="Consolas" style="font-size: 14px;">#endif</font></div>
<div><font face="Consolas" style="font-size: 14px;"> }</font></div>
<div><font face="Consolas" style="font-size: 14px;"><br>
</font></div>
<div><font face="Consolas" style="font-size: 14px;"> int m_useCount;</font></div>
<div><font face="Consolas" style="font-size: 14px;">};</font></div>
<div><font face="Consolas" style="font-size: 14px;"><br>
</font></div>
<div><font face="Consolas" style="font-size: 14px;">struct Ptr {</font></div>
<div><font face="Consolas" style="font-size: 14px;"> Ptr() { m_cntrlBlk = new CtrlBlk; }</font></div>
<div><font face="Consolas" style="font-size: 14px;"> ~Ptr() { m_cntrlBlk->decUseCount(); }</font></div>
<div><font face="Consolas" style="font-size: 14px;"> CtrlBlk* m_cntrlBlk;</font></div>
<div><font face="Consolas" style="font-size: 14px;">};</font></div>
<div><font face="Consolas" style="font-size: 14px;"><br>
</font></div>
<div><font face="Consolas" style="font-size: 14px;">void testCase() { Ptr px; }</font></div>
</blockquote>
</div>
<div><br>
</div>
<div>Would anyone have a better solution ?</div>
<div><br>
</div>
<div>Thanks,</div>
<div>Benoit</div>
<div><br>
</div>
<div>
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