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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - scan-build false positive: not realizing that "> unsigned" implies "> 0"?"
href="https://bugs.llvm.org/show_bug.cgi?id=39767">39767</a>
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<th>Summary</th>
<td>scan-build false positive: not realizing that "> unsigned" implies "> 0"?
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>7.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>FreeBSD
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Static Analyzer
</td>
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<th>Assignee</th>
<td>dcoughlin@apple.com
</td>
</tr>
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<th>Reporter</th>
<td>cperciva@freebsd.org
</td>
</tr>
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<th>CC</th>
<td>dcoughlin@apple.com, llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=21147" name="attach_21147" title="test case">attachment 21147</a> <a href="attachment.cgi?id=21147&action=edit" title="test case">[details]</a></span>
test case
The attached source file (scan-build-fp.c) has two assertions; the first
asserts that an expression is > a size_t variable, while the second is hidden
behind #ifdef SCAN_BUILD_IS_STUPID and asserts that the same expression is > 0.
It should be trivial to deduce that anything which is greater than an unsigned
value must be greater than zero, but scan-build fails to do this and yields a
false positive warning unless the > 0 condition is separately asserted:
$ scan-build70 cc -c scan-build-fp.c
scan-build: Using '/usr/local/llvm70/bin/clang-7' for static analysis
scan-build-fp.c:85:3: warning: Null pointer argument in call to memory copy
function
memcpy((uint8_t *)(EA->buf) + bufpos, buf, nbytes);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 warning generated.
scan-build: 1 bug found.
scan-build: Run 'scan-view /tmp/scan-build-2018-11-24-063313-4294-1' to examine
bug reports.
$ scan-build70 cc -c scan-build-fp.c -DSCAN_BUILD_IS_STUPID
scan-build: Using '/usr/local/llvm70/bin/clang-7' for static analysis
scan-build: Removing directory '/tmp/scan-build-2018-11-24-063309-4282-1'
because it contains no reports.
scan-build: No bugs found.</pre>
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