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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 - Unsafe optimization with inline asm using static variable defined via attribute section."
href="https://bugs.llvm.org/show_bug.cgi?id=37672">37672</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Unsafe optimization with inline asm using static variable defined via attribute section.
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Windows NT
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Frontend
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>zahira.ammarguellat@intel.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Consider this reproducer.
static const int foo __attribute__((section("bar"))) = 176;
int main(){
int x;
__asm__ ("movl foo(%rip), %eax");
__asm__ ("movl %%eax, %0 ": "=r" (x)::);
return x;
}
bash-4.2$ clang -O0 t7.c
bash-4.2$ ./a.out
bash-4.2$ echo $?
176
bash-4.2$ clang -O2 t7.c
/tmp/t7-4769e9.o: In function `main':
t7.c:(.text+0x2): undefined reference to `foo'
clang-7: error: linker command failed with exit code 1 (use -v to see
invocation)
bash-4.2$
bash-4.2$ clang -c -O0 t7.c
bash-4.2$ objdump --syms t7.o | grep foo
0000000000000000 l O bar 0000000000000004 foo
bash-4.2$ clang -c -O2 t7.c
bash-4.2$ objdump --syms t7.o | grep foo
0000000000000000 *UND* 0000000000000000 foo
bash-4.2$
Please notice that the same test case without the static specifier compiles and
runs with -O0 and -O2.</pre>
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