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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - movl nearer, %ebx in .code16 block needs to have 16-bit displacement (required by grub)"
href="https://bugs.llvm.org/show_bug.cgi?id=46952">46952</a>
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<th>Summary</th>
<td>movl nearer, %ebx in .code16 block needs to have 16-bit displacement (required by grub)
</td>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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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>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: X86
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>i@maskray.me
</td>
</tr>
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<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
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<p>
<div>
<pre>grub cannot be assembled by integrated assembler because movl nearer, %ebx in a
.code16 block has 32-bit displacement instead of 16-bit. There is a
configure-time test catching MC's discrepancy
<a href="https://github.com/coreos/grub/commit/a0bf403f66dbaca4edd8e667bfc397dd91c8d71c">https://github.com/coreos/grub/commit/a0bf403f66dbaca4edd8e667bfc397dd91c8d71c</a>
git clone <a href="https://github.com/coreos/grub">https://github.com/coreos/grub</a>
cd grub
% clang -c asm-tests/i386-pc.S
asm-tests/i386-pc.S:13:7: error: invalid .org offset '11' (at offset '14')
.org 11
^
asm-tests/i386-pc.S:13:7: error: invalid .org offset '11' (at offset '14')
.org 11
^
asm-tests/i386-pc.S:13:7: error: invalid .org offset '11' (at offset '14')
.org 11
^
The integrated assembler emits:
% llvm-mc -triple=i386 a.s --show-encoding --show-inst
.text
.code16
movl nearer, %ebx # encoding:
[0x67,0x66,0x8b,0x1d,A,A,A,A]
# fixup A - offset: 4, value: nearer,
kind: FK_Data_4
The expected GNU as behavior:
% as asm-tests/i386-pc.S -o a.o
% objdump -mi386 -Maddr16,data16 --start-address=6 -dr a.o L
a.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000006 <nearer-0x69>:
6: 66 8b 1e 00 00 mov 0x0,%ebx
9: R_X86_64_16 .text+0x6f
...
000000000000006f <nearer>:
...
0000000000000137 <far>:
...</pre>
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