dwarf-debug-format

# Install dwarfdump
apt-get install dwarfdump    # Ubuntu (part of libdwarf)
brew install libdwarf        # macOS
 
# Dump all DWARF info
dwarfdump prog
 
# Dump specific sections
dwarfdump --debug-info prog        # types, variables, functions
dwarfdump --debug-line prog        # line number table
dwarfdump --debug-loc prog         # variable locations
dwarfdump --debug-frame prog       # call frame info
 
# readelf alternatives (less verbose)
readelf --debug-dump=info prog | head -100
readelf --debug-dump=lines prog | head -50
 
# llvm-dwarfdump (more readable output)
llvm-dwarfdump prog
llvm-dwarfdump --debug-info prog | grep "DW_AT_name"
llvm-dwarfdump --statistics prog   # summarize DWARF sizes

# Sample dwarfdump output for a variable
DW_TAG_compile_unit
  DW_AT_producer  : "GNU C17 13.2.0"
  DW_AT_language  : DW_LANG_C11
  DW_AT_name      : "main.c"
  DW_AT_comp_dir  : "/home/user/project"

  DW_TAG_subprogram
    DW_AT_name    : "add"
    DW_AT_type    : <0x42>  → points to int type DIE
    DW_AT_low_pc  : 0x401130  ← function start address
    DW_AT_high_pc : 0x401150  ← function end address

    DW_TAG_formal_parameter
      DW_AT_name  : "a"
      DW_AT_type  : <0x42>
      DW_AT_location : DW_OP_reg5 (rdi)   ← lives in register rdi

    DW_TAG_formal_parameter
      DW_AT_name  : "b"
      DW_AT_location : DW_OP_reg4 (rsi)   ← lives in register rsi

# Compile with split DWARF
gcc -g -gsplit-dwarf -O2 -c main.c -o main.o
# Creates: main.o (object without full DWARF) + main.dwo (debug info)
 
# Link (linker only processes small .o files, not large DWARF)
gcc main.o -o prog
# prog references main.dwo but doesn't embed it
 
# GDB finds .dwo files via DW_AT_GNU_dwo_name attribute in prog
gdb prog    # works if main.dwo is in the same directory
 
# Inspect the split reference
readelf -S prog | grep "\.gnu_debuglink\|dwo"
dwarfdump prog | grep "dwo_name"    # shows path to .dwo files
 
# Package .dwo files into a single .dwp for distribution
dwp -o prog.dwp prog        # GNU dwp tool
llvm-dwp -o prog.dwp prog   # LLVM version
# With .dwp next to prog, GDB finds all debug info

# Client: configure to use a debuginfod server
export DEBUGINFOD_URLS="https://debuginfod.elfutils.org/"
 
# GDB uses it automatically when symbols are missing
gdb /usr/bin/git
# GDB will fetch debug symbols from debuginfod if not locally installed
 
# Explicit fetch
debuginfod-find debuginfo /usr/bin/git     # fetch debug info
debuginfod-find source /usr/bin/git        # fetch source
 
# Distribution servers
# Fedora:  https://debuginfod.fedoraproject.org/
# Ubuntu:  https://debuginfod.ubuntu.com/
# Debian:  https://debuginfod.debian.net/
# elfutils: https://debuginfod.elfutils.org/
 
# Configure in GDB
(gdb) set debuginfod enabled on
(gdb) set debuginfod verbose 1
 
# Set up your own debuginfod server
debuginfod -d /var/cache/debuginfod -p 8002 /path/to/binaries/
export DEBUGINFOD_URLS="http://localhost:8002"

# Full LTO: DWARF is generated after link-time optimization
# Variables and functions may be merged, inlined, or eliminated
gcc -flto -O2 -g main.c util.c -o prog
# DWARF in prog reflects post-LTO state (may lose some info)
 
# Thin LTO (better for debug info preservation)
clang -flto=thin -O2 -g main.c util.c -o prog
 
# For best debug info with LTO: use -Og or separate debug build
gcc -Og -g main.c util.c -o prog_debug     # no LTO, full debug
gcc -O2 -flto main.c util.c -o prog_fast   # LTO, limited debug
 
# Rust: LTO discard debug info by default in non-release profiles
[profile.dev]
lto = "off"    # preserves debug info

# Strip binary (remove DWARF for distribution)
strip --strip-debug prog -o prog.stripped
 
# Keep separate debug file
objcopy --only-keep-debug prog prog.debug
strip --strip-debug prog
# Link stripped binary to its debug file
objcopy --add-gnu-debuglink=prog.debug prog
 
# GDB finds debug file automatically
gdb prog    # loads prog.debug via .gnu_debuglink
 
# Or use eu-strip (elfutils) — creates both in one step
eu-strip -f prog.debug prog
 
# Verify debug link
readelf -n prog | grep "Debug\|debuglink"
 
# Check DWARF size contribution
llvm-dwarfdump --statistics prog | grep "file size"
size --format=SysV prog | sort -k2rn | head -15