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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 - llvm-symbolizer does not support .gnu_debugaltlink"
href="https://bugs.llvm.org/show_bug.cgi?id=47537">47537</a>
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<th>Summary</th>
<td>llvm-symbolizer does not support .gnu_debugaltlink
</td>
</tr>
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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>All
</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>DebugInfo
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>iii@linux.ibm.com
</td>
</tr>
<tr>
<th>CC</th>
<td>jdevlieghere@apple.com, keith.walker@arm.com, llvm-bugs@lists.llvm.org, paul_robinson@playstation.sony.com
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<pre>I noticed that llvm-symbolizer fails to fully symbolize python3-related
backtraces on s390x Fedora 31. I tracked this down to lack of .gnu_debugaltlink
support, so I'm fairly confident the problem occurs on other architectures as
well.
For example:
$ llvm-project/build/bin/llvm-symbolizer -e /usr/lib64/libpython3.7m.so.1.0
0x3fffcf998c3 --adjust-vma 0x3fffcf00000
??
/usr/src/debug/python3-3.7.4-5.fc31.s390x/Objects/obmalloc.c:1585:11
??
/usr/src/debug/python3-3.7.4-5.fc31.s390x/Objects/obmalloc.c:1577:1
Surprisingly, llvm-symbolizer shows the correct source code lines, but no
function names.
If we extract relevant DIE offsets with the debugger and dig into libpython3
debuginfo, we'll see:
<1><25eac>: Abbrev Number: 40 (DW_TAG_subprogram)
<25ead> DW_AT_abstract_origin: <alt 0x10f7a>
<25eb1> DW_AT_low_pc : 0x99850
<25eb9> DW_AT_high_pc : 148
<25ebb> DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa)
<25ebd> DW_AT_GNU_all_call_sites: 1
<25ebd> DW_AT_sibling : <0x25f58>
DW_AT_abstract_origin points to <alt 0x10f7a>, so the target DIE is in a file
pointed to by .gnu_debugaltlink. As far as I understand, dwz produces these
when deduplicating debuginfo.
And indeed:
Contents of section .gnu_debugaltlink:
0000 2e2e2f2e 2e2f2e64 777a2f70 7974686f ../../.dwz/pytho
0010 6e332d33 2e372e34 2d352e66 6333312e n3-3.7.4-5.fc31.
0020 73333930 7800467e 07ea9a25 a5feb0ca s390x.F~...%....
0030 82f3ed5f 3ebb73aa 698e ..._>.s.i.
If we look into
/usr/lib/debug/usr/lib64/libpython3.7m.so.1.0-3.7.4-5.fc31.s390x.debug, we'll
find:
<1><10f7a>: Abbrev Number: 26 (DW_TAG_subprogram)
<10f7b> DW_AT_name : (indirect string, offset: 0x19edc):
_PyObject_Malloc
<10f7f> DW_AT_decl_file : 200
<10f80> DW_AT_decl_line : 1577
<10f82> DW_AT_decl_column : 1
<10f83> DW_AT_prototyped : 1
<10f83> DW_AT_type : <0x52df7>
<10f87> DW_AT_sibling : <0x10fb1>
_PyObject_Malloc is exactly the missing function name.
It would be great if .gnu_debugaltlink support could be added to
llvm-symbolizer. I see that lldb already has it.</pre>
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