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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - -mlong-double-64/80/128 documentation incomplete"
href="https://bugs.llvm.org/show_bug.cgi?id=43666">43666</a>
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<th>Summary</th>
<td>-mlong-double-64/80/128 documentation incomplete
</td>
</tr>
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<th>Product</th>
<td>Documentation
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>General docs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>tydeman@tybor.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>Assuming that clang is implementing the same as gcc, the documentation of
-mlong-double-64/80/128 in
<a href="https://clang.llvm.org/docs/ClangCommandLineReference.html">https://clang.llvm.org/docs/ClangCommandLineReference.html</a> fails to mention
that changing the size of long double does NOT change the ABI. Therefore,
calls to functions that use long doubles, eg, <math.h>, scanf(), printf(), ...,
will produce strange results.
gcc documentation has:
Warning: if you override the default value for your target ABI,
this changes the size of structures and arrays containing "long
double" variables, as well as modifying the function calling
convention for functions taking "long double". Hence they are
not binary-compatible with code compiled without that switch.</pre>
</div>
</p>
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