DWARF Expert

Expertise for DWARF debug info: parsing and searching it, verifying its
integrity, answering questions about the standard, and writing code that
consumes it. Out of scope: runtime debugging (use gdb/lldb), reverse
engineering beyond the DWARF sections (use Ghidra/IDA), and compiler-specific
DWARF generation bugs.

Authoritative Sources

When precision matters, look standard details up instead of answering from memory:

1. dwarfstd.org — the official specification. Web-search specific sections,
   e.g. "DWARF5 DW_TAG_subprogram attributes site:dwarfstd.org".
2. LLVM — llvm/lib/DebugInfo/DWARF/ is a reliable reference implementation:
   DWARFDie.cpp (DIE and attribute access), DWARFUnit.cpp (compilation units),
   DWARFDebugLine.cpp (line tables), DWARFVerifier.cpp (validation).
3. libdwarf — the reference C implementation at github.com/davea42/libdwarf-code.

Parsing and Searching with dwarfdump

Prefer dwarfdump over readelf for DWARF-specific work. Two implementations
exist — libdwarf's dwarfdump and LLVM's llvm-dwarfdump — with different
options, and a bare dwarfdump command may be either: check dwarfdump --version
first. The options below are LLVM's.

On macOS, linked Mach-O executables do not carry DWARF: it stays in the .o
files until dsymutil collects it into a .dSYM bundle. Point dwarfdump at
the dSYM (or the object files), not the executable. pyelftools is ELF-only —
for Mach-O scripted work, stay with the LLVM tools.

• --all: dump every DWARF section; --debug-info, --debug-line, etc. dump one
• --show-children [--recurse-depth=<n>]: include child DIEs when printing
  selected entries — parameters, locals, and struct members are children of
  function and type DIEs
• --show-parents [--parent-recurse-depth=<n>]: include parent DIEs
• --show-form: print attribute form types, for when encoding details matter
• --find=<name>: exact-name lookup via the accelerator tables — fast but not
  exhaustive; fall back to --name when it misses
• --name=<pattern> [--ignore-case] [--regex]: exhaustive DIE-name search
• --lookup=<address>: find the DIE covering an address
• --verbose: print low-level encoding detail

Searching DIEs

Escalate through these strategies as the query grows more complex:

1. Name or address match: --find, then --name; --lookup for addresses.
2. Attribute or type queries (e.g. all parameters of type float *): dump and
   filter. grep -B pulls in the header line carrying each DIE's offset:
   llvm-dwarfdump file | grep -B 5 "float \*" | grep DW_TAG_formal_parameter,
   then print each DIE at its offset with --debug-info=<offset> --show-children
   (--lookup takes a program address, not a DIE offset).
3. Multi-attribute or structural queries: when grep pipelines turn brittle,
   write a Python script using pyelftools instead.

Verifying DWARF Integrity

• llvm-dwarfdump --verify <binary>: structural checks (unit chains, DIE
  relationships, address ranges). --error-display=<quiet|summary|details|full>
  controls detail; --verify-json=<path> writes a machine-readable error
  summary; --quiet for exit-code-only checks.
• llvm-dwarfdump --statistics <binary>: debug-info quality metrics as JSON —
  compare across compiler versions or optimization levels to catch regressions.

Verify after producing DWARF (compilers, binary rewriters), when a debugger
misbehaves on a binary, and when developing DWARF tooling against known-good
files.

When a current-generation compiler emitted an old DWARF version, the build
explicitly passed -gdwarf-N — modern gcc and clang default to v4/v5, so check
the build system rather than assuming a toolchain default. GCC embeds its flags
in DW_AT_producer, so the pin is often readable right there; clang's producer
string carries no flags. Old versions remain common in the wild and read the
same way apart from surface forms: in v2 output, member offsets appear as
location expressions (DW_OP_plus_uconst) and linkage names as
DW_AT_MIPS_linkage_name.

readelf

For general ELF structure, or when dwarfdump is unavailable:

• --debug-dump=<section>: dump a DWARF section (info, line, ...)
• --dwarf-depth=<n> / --dwarf-start=<n>: limit DIE depth / start offset

Writing Code That Parses DWARF

Prefer an existing library over parsing by hand:

Default to Python with pyelftools for one-off scripts unless the task dictates
otherwise.

DWARF-specific pitfalls to handle — and to check for when reviewing DWARF code:

• Attributes are optional: a DIE may omit DW_AT_name, DW_AT_type, ranges, etc.
• Attribute indirection: a DIE's attributes may live on the DIE referenced by its
  DW_AT_abstract_origin (inlined instances) or DW_AT_specification
  (out-of-line definitions) — resolve the chain before concluding data is absent.
• Type chains: qualifiers and modifiers (DW_TAG_const_type,
  DW_TAG_pointer_type, ...) wrap the underlying type; walk DW_AT_type links to
  reach the base type.