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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 - Unreachable triggered when parsing DWARF V5 line table with unsupported FORM"
href="https://bugs.llvm.org/show_bug.cgi?id=44260">44260</a>
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<th>Summary</th>
<td>Unreachable triggered when parsing DWARF V5 line table with unsupported FORM
</td>
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<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>DebugInfo
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>jh7370.2008@my.bristol.ac.uk
</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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<div>
<pre>I ran into this when writing some llvm-dwarfdump tests. If a DWARF V5
.debug_line table header includes a file name or directory entry type with an
unsupported FORM value, and llvm-dwarfdump is used to dump the said line table,
an llvm_unreachable is triggered when parsing that field.
// example assembly
.section .debug_line,"",@progbits
.long .Lunit0_end - .Lunit0_begin # unit_length
.Lunit0_begin:
.short 5 ## version
.byte 8 ## address_size
.byte 0 ## segment_selector_size
.long .Lheader0_end - .Lheader0_begin ## header_length
.Lheader0_begin:
.byte 1 ## minimum_instruction_length
.byte 1 ## maximum_operations_per_instruction
.byte 1 ## default_is_stmt
.byte -5 ## line_base
.byte 7 ## line_range
.byte 13 ## opcode_base
.byte 0, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1 ## standard_opcode_lengths
.byte 1 ## directory_entry_format_count
.byte 0x1, 0x7F ## DW_LNCT_path, unknown form
.byte 1 ## directories_count
.byte 0 ## directory entry 0
.asciz "dir1/dir2"
.byte 1 ## file_name_entry_format_count
.byte 0x1, 0xB ## DW_LNCT_path, DW_FORM_string
.byte 0x2, 0x5 ## DW_LNCT_directory_index, DW_FORM_data1
.byte 2 ## file_names_count
.byte 0 ## file name entry 0
.asciz "file1.c"
.byte 1 ## file name entry 1
.long 0x12345678
.Lheader0_end:
.Lunit0_end:
C:\Work> llvm-dwarfdump --debug-line test.o
test.o: file format ELF64-x86-64
.debug_line contents:
debug_line[0x00000000]
unsupported form
UNREACHABLE executed at
C:\llvm\llvm-project\llvm\lib\DebugInfo\DWARF\DWARFFormValue.cpp:350!
<stack dump...>
The unreachable has an associated comment which seems to imply that the
extractValue code was written for parsing .debug_info, and as such unsupported
DW_FORM_* values are not handled (because they should be handled earlier).
Clearly the code needs updating to allow for DW_FORM_* values coming from
.debug_line. It's probably reasonable to abort parsing of the line table when
an unsupported DW_FORM_* is hit, since it's impossible to know how to handle
the file/directory table in this case.</pre>
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