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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Regression: Referencing labels across asm blocks results in bad asm since 4.0.0"
href="https://bugs.llvm.org/show_bug.cgi?id=34708">34708</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Regression: Referencing labels across asm blocks results in bad asm since 4.0.0
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>4.0
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>C++
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>llvm@thecybershadow.net
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>///////////// test.cpp ////////////
bool test()
{
__asm mov byte ptr [magic], 0x90;
__asm {
magic:
nop
};
}
///////////////////////////////////
$ clang -c -m32 -target i386-pc-windows-msvc18.0.0 test.cpp
test.cpp:3:3: error: assembler label 'L__MSASMLABEL_.0__magic' can not be
undefined
__asm mov byte ptr [magic], 0x90;
^
<inline asm>:2:2: note: instantiated into assembly here
mov byte ptr L__MSASMLABEL_.0__magic, 0x90
^
1 error generated.
Looking at the emitted assembly, it looks like Clang/LLVM uses the
"L__MSASMLABEL_.0__magic" label when referring to the address of the "magic"
label, but actually defines the label with the name "L__MSASMLABEL_.1__magic".
In 3.9.1 "L__MSASMLABEL_.0__magic" is used throughout.
This pattern is necessary for MSVC compatibility with programs using
self-modifying code.</pre>
</div>
</p>
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