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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - llvm-readobj reads past end of dynamic segment if it does not end in DT_NULL"
href="https://bugs.llvm.org/show_bug.cgi?id=40861">40861</a>
</td>
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<th>Summary</th>
<td>llvm-readobj reads past end of dynamic segment if it does not end in DT_NULL
</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>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>llvm-readobj
</td>
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<tr>
<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>jh7370.2008@my.bristol.ac.uk, llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>Generating a dynamic segment with the following yaml results in there being no
DT_NULL entry at the end of the segment:
--- !ELF
FileHeader:
Class: ELFCLASS64
Data: ELFDATA2LSB
Type: ET_EXEC
Machine: EM_X86_64
Sections:
- Name: .dynamic
Type: SHT_DYNAMIC
AddressAlign: 0x10
Address: 0x1010
# DT_DEBUG tag only, no DT_NULL tag.
Content: "15000000000000000000000000000000"
ProgramHeaders:
- Type: PT_LOAD
VAddr: 0x1000
Sections:
- Section: .dynstr
- Section: .dynamic
- Type: PT_DYNAMIC
VAddr: 0x1010
Sections:
- Section: .dynamic
Although strictly speaking this is illegal, GNU readelf handles it sensibly,
because the size is listed in the program header:
C:\Work> readelf --dynamic test.tmp.no-null
Dynamic section at offset 0x1f0 contains 1 entries:
Tag Type Name/Value
0x0000000000000015 (DEBUG) 0x0
However, llvm-readobj does not. It assumes that there is always a trailing
DT_NULL entry, and reads past the end of the segment if there is none to find
it:
C:\Work> llvm-readobj.exe --dynamic-table test.tmp.no-null
<snip>
DynamicSection [ (2 entries)
Tag Type Name/Value
0x0000000000000015 DEBUG 0x0
0x0000000000000000 NULL 0x0
]
I'm guessing, but don't know for sure, that the non-existent NULL entry is
printed as such because the next 16 bytes happen to be all 0 in the file.</pre>
</div>
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