extract-asm

Prerequisites

The input must be a compiled object file (.o or .obj) or assembly file (.s or .asm). If you have source code, compile it first (e.g. via CMake build or standalone clang -S).

Arguments

• $1 = input file (.o, .obj, .s, or .asm)
• $2 = function name (optional — if omitted, disassemble the entire file)

Examples:

• trees.c.o compress_block — single function
• trees.c.o — entire file
• trees.s my_function
• trees.obj compress_block

Steps

1. Disassemble object files (.o / .obj)

Use the appropriate tool for the platform:

Platform	Tool	Notes
macOS	llvm-objdump	Ships with Xcode
Linux	objdump	GNU binutils 2.32+
Windows	llvm-objdump	Ships with VS LLVM/clang workload or standalone LLVM

Single function ($2 provided):

Platform	Command
macOS	llvm-objdump --disassemble-symbols=_<name> --no-show-raw-insn <file>
Linux	objdump --disassemble=<name> --no-show-raw-insn <file>
Windows	llvm-objdump --disassemble-symbols=<name> --no-show-raw-insn <file>

Entire file ($2 omitted):

Platform	Command
macOS	llvm-objdump -d --no-show-raw-insn <file>
Linux	objdump -d --no-show-raw-insn <file>
Windows	llvm-objdump -d --no-show-raw-insn <file>

Windows dumpbin fallback — if llvm-objdump is not available:

VSPATH=$(vswhere -latest -property installationPath)
cmd.exe /c "call \"${VSPATH}\VC\Auxiliary\Build\vcvarsall.bat\" amd64 >nul 2>&1 && dumpbin /disasm <file>.obj"

Then manually extract the function: find <function_name>: label, collect until the next label or summary line.

2. Extract from assembly files (.s / .asm)

Read the file directly. If $2 is provided, extract the named function:

• Mach-O: Find _<function_name>:, collect until next ^_[a-zA-Z] label (excluding _Ltmp, _LCFI, _LBB prefixes).
• ELF/other: Find <function_name>:, collect until the next function label.

3. Clean up and output

• Filter out assembler directives (. prefix), comments (#, ;, //, @), and blank lines
• Keep only instruction lines
• Output the assembly to stdout with a summary line showing the instruction count

Symbol Names

Symbol names differ by platform — use this when passing to --disassemble-symbols or searching in .s files:

Platform	C function foo	C++ function foo
macOS (Mach-O)	_foo	_Z3foov (Itanium mangled, _ prefixed)
Linux (ELF)	foo	_Z3foov (Itanium mangled)
Windows (PE/COFF)	foo	?foo@@YAXXZ (MSVC decorated)

Architecture Notes

Architecture	Key details
x86-64	offset(%reg) memory syntax. leaq (%rip) is PC-relative, not a load.
AArch64	[reg, #offset] memory syntax. Loads: ldr, ldur, ldp, ldrb, ldrh, ldrsw. Stores: str, stur, stp, strb, strh. Apple Silicon compiles natively.
x86-64 (MSVC)	Intel syntax (dest first): mov rax, [rcx+168]. Args in rcx, rdx, r8, r9. C++ names may be decorated (?name@@...).

CMake Build Paths

• Unix: build/CMakeFiles/<target>.dir/<source>.o
• Windows (Ninja): build/CMakeFiles/<target>.dir/<source>.obj
• Windows (VS): build/CMakeFiles/<target>.dir/<config>/<source>.obj