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Binutils 2.45.1 (binary only)⚓︎

Overview⚓︎

Binary analysis and manipulation utilities from GNU Binutils package plus patchelf. Essential for debugging, inspecting, and analyzing ELF binaries.

Installation⚓︎

Select in menuconfig: 

Debug helpers ---> binary-tools

Available Tools⚓︎

All tools operate on ELF (Executable and Linkable Format) binaries:

  • readelf - Display information about ELF files (headers, sections, symbols)
  • objdump - Display object file information (disassembly, sections)
  • objcopy - Copy and translate object files
  • nm - List symbols from object files
  • strings - Print printable strings from binary files
  • ar - Create, modify, and extract from archives (.a files)
  • ranlib - Generate index for archive contents
  • strip - Discard symbols and debug information from binaries
  • addr2line - Convert addresses to file/line numbers (debugging)
  • size - List section sizes and total size of binaries
  • patchelf - Modify ELF dynamic linker and RPATH (runtime library paths)

Usage Examples⚓︎

Inspecting Binaries⚓︎

# Display ELF header information
readelf -h /usr/bin/python3

# List all symbols in a binary
nm /usr/bin/python3

# Disassemble a binary (MIPS assembly)
objdump -d /usr/bin/python3

# Show dynamic library dependencies
readelf -d /usr/bin/python3 | grep NEEDED

# Display section sizes
size /usr/bin/python3

Debugging⚓︎

# Find source location of crash address
addr2line -e /usr/bin/python3 0x00400abc

# Extract strings from binary (useful for reverse engineering)
strings /usr/bin/python3 | grep -i "error"

# Check if binary is stripped
file /usr/bin/python3

Binary Manipulation⚓︎

# Strip debug symbols to reduce size
strip --strip-debug /tmp/mybinary

# Create static library archive
ar rcs libmylib.a obj1.o obj2.o obj3.o
ranlib libmylib.a

# Copy binary and change section names
objcopy --rename-section .data=.rodata mybinary mybinary.new

# Fix dynamic linker path (useful for Freetz-NG SEPARATE_AVM_UCLIBC)
patchelf --set-interpreter /usr/lib/freetz/ld-uClibc.so.1 /usr/bin/mybinary

# Change RPATH to use custom library location
patchelf --set-rpath /usr/lib/freetz /usr/bin/mybinary

# View current interpreter and RPATH
patchelf --print-interpreter /usr/bin/mybinary
patchelf --print-rpath /usr/bin/mybinary

Common Use Cases⚓︎

1. Debugging Crashes⚓︎

When a program crashes, use readelf and addr2line to identify the problem:

# Program crashed at address 0x00405678
readelf -s /usr/bin/myprogram | grep "00405678"
addr2line -e /usr/bin/myprogram 0x00405678

2. Analyzing Dependencies⚓︎

Check which libraries a binary needs:

readelf -d /usr/bin/python3 | grep NEEDED
# Output shows required .so files

3. Fixing Dynamic Linker Issues⚓︎

When binaries fail with "not found" errors for the dynamic linker:

# Check current interpreter
readelf -l /usr/bin/mybinary | grep interpreter

# Fix it with patchelf
patchelf --set-interpreter /usr/lib/freetz/ld-uClibc.so.1 /usr/bin/mybinary

# Verify the change
readelf -l /usr/bin/mybinary | grep interpreter

This is especially useful when cross-compiling binaries or when using FREETZ_SEPARATE_AVM_UCLIBC=y.

4. Reverse Engineering⚓︎

Extract information from unknown binaries:

# Find human-readable strings
strings /bin/unknown_binary

# List exported functions
nm -D /lib/libssl.so.1.1

# Disassemble specific function
objdump -d /usr/bin/binary | grep -A 20 "function_name"

4. Reducing Binary Size⚓︎

Strip unnecessary symbols:

# Before
size mybinary
# text    data     bss     dec     hex filename
# 123456  45678   12345  181479  2c4e7 mybinary

# Strip debug info
strip --strip-debug mybinary

# After (smaller)
size mybinary

Integration with GCC Toolchain⚓︎

Binary-tools is automatically selected when installing the full GCC toolchain:

Debug helpers ---> GCC (Native Compiler for On-Device Compilation)
  [ ] Minimal installation (GCC + essential tools only)

Minimal installation: Includes only ld, as, ar, ranlib (essential for compilation) Full installation: Includes all binary-tools utilities

Troubleshooting⚓︎

"command not found"⚓︎

Binary-tools must be externalized to USB storage:

# Check if tools are externalized
ls -la /var/media/ftp/uStor01/freetz-external/binary-tools/

# If not, run externalization
modsave flash

Wrong Architecture Binaries⚓︎

Binary-tools are MIPS binaries that run on the router. They analyze any architecture's ELF files, but they themselves must run on MIPS.

# This works (MIPS binary analyzing x86 file)
readelf -h /tmp/x86_binary.elf

# This won't work (trying to run x86 binary on MIPS router)
./x86_binary
# bash: ./x86_binary: cannot execute binary file

Performance Considerations⚓︎

  • objdump -d (disassembly) on large binaries can be slow
  • Use grep to filter output: objdump -d binary | grep pattern
  • Consider copying binaries to RAM for faster analysis: cp /var/media/ftp/file /tmp/

See Also⚓︎