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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - miscompilation: %rbx is reused across cpuid"
href="http://llvm.org/bugs/show_bug.cgi?id=17907">17907</a>
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<th>Summary</th>
<td>miscompilation: %rbx is reused across cpuid
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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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>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>new bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>kcc@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=11531" name="attach_11531" title="bug.ll">attachment 11531</a> <a href="attachment.cgi?id=11531&action=edit" title="bug.ll">[details]</a></span>
bug.ll
I have a cpuid function implemented like this:
void __cpuid(int cpu_info[4], int info_type) {
__asm__ volatile("cpuid \n\t"
: "=a"(cpu_info[0]), "=b"(cpu_info[1]), "=c"(cpu_info[2]),
"=d"(cpu_info[3])
: "a"(info_type));
}
The asm constraints look correct -- they say that the instruction clobbers %rbx
However in some circumstances, the codegen doesn't seem to honor this.
This happens when I build a .cc files with locally modified AddressSanitizer.
I don't have a proper .cc example, only a .ll example:
% llc bug.ll
pushq %rbx
...
movq %rsp, %rbx
...
cpuid
movq 128(%rbx), %rsi
Here %rbx is used right after cpuid which clobbers %rbx
So far I was not able to reproduce this bug w/o my local modification in
AddressSanitizer.
Any suggestion?</pre>
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