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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 - [X86_32] Miscompilation with __llvm_retpoline_push"
href="https://bugs.llvm.org/show_bug.cgi?id=36329">36329</a>
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<th>Summary</th>
<td>[X86_32] Miscompilation with __llvm_retpoline_push
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>6.0
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: X86
</td>
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<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>dwmw2@infradead.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=19849" name="attach_19849" title="Config file for kernel build">attachment 19849</a> <a href="attachment.cgi?id=19849&action=edit" title="Config file for kernel build">[details]</a></span>
Config file for kernel build
After a call via __llvm_retpoline_push, code in the calling function seems
confused about where %esp points.
Reproduced with llvm/clang master (r324745 / r324741 resp.) and also with 6.0
branch (r324726 / r324719 resp) with r326645 added to the latter.
To reproduce:
git clone git://git.infradead.org/linux-retpoline.git
cd linux-retpoline
git checkout clang
cp /where/you/downloaded/the/attached/config .config
make CC=/where/is/your/clang bzImage
qemu-system-i386 -display none -serial stdio -kernel arch/x86/boot/bzImage
-append earlyprintk=ttyS0,keep
Observe the output from mp_register_ioapic():
[ 0.000000] mp_register_ioapic, 0 fec00000 0 c1b31e88
[ 0.000000] At line 412, gsi_base is 0
[ 0.000000] At line 425, gsi_base is -1043707140
[ 0.000000] At line 427, gsi_base is -1043707140
Between line 412 and 425, gsi_base got clobbered.
Now uncomment the CFLAGS_io_apic_b line in arch/x86/kernel/apic/Makefile and
repeat, to disable the retpoline. Observe the problem go away.
To eliminate the external thunks as a cause of this problem, also retest with
CFLAGS_io_apic_b.o += -mno-retpoline-external-thunk -mretpoline
The problem persists even when we let LLVM emit its own thunks.</pre>
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