How to use
- Copy the installation command and review the source package before installing it in your own agent environment.
- Check the source document for required tools, credentials and supported hosts.
- Describe your input and desired deliverable; review the output against the source material.
npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill elf-inspectionBefore you start
- Installation does not include a model subscription, API allowance or permission to access your files.
- Repository stars and installation counts describe activity, not an independent quality or security test.
Original skill document
Rendered from the source repository. Headings, examples, code, tables, links, and referenced images are preserved.
ELF Inspection
Purpose
Guide agents through inspecting Linux ELF binaries: symbol tables, section layout, dynamic linking, debug info, and diagnosing linker errors.
Triggers
- "What libraries does this binary depend on?"
- "Why is this binary so large?"
- "I have an
undefined referenceor symbol not found at runtime" - "How do I check if debug info is in this binary?"
- "How do I find what symbols a library exports?"
- "How do I check if a binary is PIE / has RELRO?"
Workflow
1. Quick overview: file and size
bash
file prog # type, arch, linkage, stripped or not
size prog # section sizes: text, data, bss
size --format=sysv prog # detailed per-section breakdown2. Dynamic dependencies: ldd
bash
ldd ./prog # show all shared lib dependencies
ldd -v ./prog # verbose: include symbol versions
# Check why a library is loaded
ldd ./prog | grep libssl
# For a library (not an executable)
ldd ./libfoo.soIf ldd shows not found, the shared library is missing from LD_LIBRARY_PATH or /etc/ld.so.conf.
Fix:
bash
export LD_LIBRARY_PATH=/path/to/libs:$LD_LIBRARY_PATH
# Or install the library and run ldconfig
sudo ldconfig3. Symbols: nm
bash
nm prog # all symbols (T=text, D=data, U=undefined, etc.)
nm -D ./libfoo.so # dynamic symbols only
nm -C prog # demangle C++ symbols
nm --defined-only prog # only defined symbols
nm -u prog # only undefined (needed) symbols
nm -S prog # include symbol size
# Search for a symbol
nm -D /usr/lib/libssl.so | grep SSL_readSymbol type codes:
T/t— text (code): global / localD/d— data (initialised): global / localB/b— BSS (uninitialised): global / localR/r— read-only data: global / localU— undefined (needs to be provided at link time)W/w— weak symbol
4. Sections: readelf
bash
readelf -h prog # ELF header (arch, type, entry point)
readelf -S prog # all sections
readelf -l prog # program headers (segments)
readelf -d prog # dynamic section (like ldd but raw)
readelf -s prog # symbol table
readelf -r prog # relocations
readelf -n prog # notes (build ID, ABI tag)
readelf --debug-dump=info prog | head -100 # DWARF info
readelf -a prog # all of the above5. Disassembly and source: objdump
bash
# Disassemble all code sections
objdump -d prog
objdump -d -M intel prog # Intel syntax
# Disassemble + intermix source (needs -g at compile time)
objdump -d -S prog
# Disassemble specific symbol
objdump -d prog | awk '/^[0-9a-f]+ <main>:/,/^$/'
# All sections (including data)
objdump -D prog
# Header info
objdump -f prog
objdump -p prog # private headers (including needed libs)6. Binary hardening check
bash
# Check for PIE, RELRO, stack canary, NX
# Use checksec (install separately)
checksec --file=prog
# Manual checks:
readelf -h prog | grep Type # ET_DYN = PIE, ET_EXEC = non-PIE
readelf -d prog | grep GNU_RELRO # RELRO present
readelf -d prog | grep BIND_NOW # full RELRO
readelf -s prog | grep __stack_chk # stack protector
readelf -l prog | grep GNU_STACK # NX bit (RW = no exec, RWE = exec stack)7. Section size analysis (binary bloat)
bash
# Detailed section sizes
size --format=sysv prog | sort -k2 -nr | head -20
# Per-object contribution (with -Wl,--print-map or bloaty)
# Bloaty (install separately): https://github.com/google/bloaty
bloaty prog
# Check stripped vs not
file prog
strip --strip-all -o prog.stripped prog
ls -lh prog prog.stripped8. Build ID
Build IDs uniquely identify a binary/library build, enabling debuginfod lookups.
bash
readelf -n prog | grep 'Build ID'
# or
file prog | grep BuildID9. Common diagnosis flows
"undefined symbol at runtime"
bash
# Which library was expected to provide it?
nm -D libfoo.so | grep mysymbol
# Is the library in the runtime path?
ldd ./prog | grep libfoo
# Check LD_PRELOAD / LD_LIBRARY_PATH"binary is too large"
bash
size --format=sysv prog | sort -k2 -nr | head
nm -S --defined-only prog | sort -k2 -nr | head -20
objdump -d prog | awk '/^[0-9a-f]+ </{fn=$2} /^[0-9a-f]/{count[fn]++} END{for(f in count) print count[f], f}' | sort -nr | head -20For a quick reference, see references/cheatsheet.md.
Related skills
- Use
skills/binaries/linkers-ltofor linker flags and LTO - Use
skills/binaries/binutilsforar,strip,objcopy,addr2line - Use
skills/debuggers/core-dumpsfor build ID and debuginfod usage
