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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - -Wformat check is not correct when using bitfield parameters"
href="https://llvm.org/bugs/show_bug.cgi?id=30533">30533</a>
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<th>Summary</th>
<td>-Wformat check is not correct when using bitfield parameters
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>unspecified
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Frontend
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>arichardson.kde@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>I noticed that one of my printfs was outputting garbage values even though I
compile with -Werror=format.
Abbreviated example:
struct foo {
uint64_t a : 10;
uint64_t b : 12;
uint64_t c : 10
};
foo f;
f.b = 0xab;
printf("Foo.b: %llx", f.b);
This usually gave me random garbage like Foo.b:7fa0000000ab (always with the
correct value at the end). It seems to me that the f.b is being passed as a 32
bit int on the stack but because it is declared as a uint64_t bitfield the
-Wformat check assumes that %llx is okay.
clang --version
clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin</pre>
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