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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Unstable call instruction disassembly output if empty sections in linked ELF"
href="https://bugs.llvm.org/show_bug.cgi?id=45411">45411</a>
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<th>Summary</th>
<td>Unstable call instruction disassembly output if empty sections in linked ELF
</td>
</tr>
<tr>
<th>Product</th>
<td>tools
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Windows NT
</td>
</tr>
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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>
</tr>
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<th>Component</th>
<td>llvm-objdump
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>jh7370.2008@my.bristol.ac.uk
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>If a fully-linked ELF (i.e. not ET_REL) containing empty sections is
disassembled, the output of call instructions may be unstable - the symbol
referenced may change between runs, even though the input is unchanged. My
guess is that the use of partition_point does not work reliably when there are
multiple sections with the same address - it appears to sometimes pick the
empty section and therefore not use the symbols from the right section at all.
More generally, the disassembler probably shouldn't be using section
information in identifying symbols at all when disassembling a fully linked
ELF, but perhaps that's outside the scope of this issue.
Reproducible (in all cases, "bob" should be picked, not the absolute symbol):
// bar.s
.global _start
.global bob
.global abs
abs = 1
.section .section.call,"ax",@progbits
_start:
call bob@PLT
.section .section.empty,"ax"
.section .section.bob,"ax"
bob:
ret
C:\Work\TempWork> C:\llvm\build\Debug\bin\clang.exe -c bar.s
C:\Work\TempWork> C:\llvm\build\Debug\bin\ld.lld.exe bar.o -o bar.elf
C:\Work\TempWork> C:\llvm\build\Debug\bin\llvm-objdump -d bar.elf
bar.elf: file format elf64-x86-64
Disassembly of section .section.call:
0000000000201120 <_start>:
201120: e8 00 00 00 00 callq 0x201125 <abs+0x201124>
Disassembly of section .section.bob:
0000000000201125 <bob>:
201125: c3 retq
C:\Work\TempWork> C:\llvm\build\Debug\bin\llvm-objdump -d bar.elf
bar.elf: file format elf64-x86-64
Disassembly of section .section.call:
0000000000201120 <_start>:
201120: e8 00 00 00 00 callq 0x201125 <bob>
Disassembly of section .section.bob:
0000000000201125 <bob>:
201125: c3 retq</pre>
</div>
</p>
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