nodejs/node · error · RuntimeError

Unable to locate a compiler for preprocessing assembly

Error message

Unable to locate a compiler for preprocessing assembly

What it means

preprocess_asm.py needs a C/C++ compiler to run the preprocessor (-E -P) over .S assembly sources before handing them to an assembler. find_compiler() first honors CC then CXX, then falls back to a hard-coded list (cl.exe, clang-cl, cc, clang, gcc); if none resolves to an executable on PATH, it raises RuntimeError.

Source

Thrown at deps/libffi/preprocess_asm.py:33

        return None
    value = value.strip()
    if not value:
        return None
    return shlex.split(value, posix=(os.name != 'nt'))


def find_compiler():
    for var in ('CC', 'CXX'):
        command = split_command(os.environ.get(var))
        if command and shutil.which(command[0]):
            return command

    for name in ('cl.exe', 'cl', 'clang-cl.exe', 'clang-cl', 'cc', 'clang', 'gcc'):
        path = shutil.which(name)
        if path:
            return [path]

    raise RuntimeError('Unable to locate a compiler for preprocessing assembly')


def find_armasm64():
    """Find armasm64.exe in the PATH or common Visual Studio locations."""
    # First check PATH
    path = shutil.which('armasm64.exe')
    if path:
        return path

    # Check common VS locations via environment
    vc_install_dir = os.environ.get('VCINSTALLDIR', '')
    if vc_install_dir:
        candidate = os.path.join(vc_install_dir, 'bin', 'Hostx64', 'arm64', 'armasm64.exe')
        if os.path.exists(candidate):
            return candidate
        candidate = os.path.join(vc_install_dir, 'bin', 'Hostarm64', 'arm64', 'armasm64.exe')
        if os.path.exists(candidate):
            return candidate

View on GitHub (pinned to 1b2de5e052)

Solutions

1. Export CC (or CXX) pointing at your compiler, e.g. `export CC=clang`.
2. Ensure the compiler is on PATH (run vcvarsall.bat / activate the toolchain on Windows; install build-essential/clang on Linux).
3. If shelling out from a build system, propagate the same CC it uses to this script's environment.

Example fix

# before: empty toolchain env
python preprocess_asm.py --input src/aarch64/sysv.S --output out.s
# after
export CC=clang
python preprocess_asm.py --input src/aarch64/sysv.S --output out.s

import os, shutil
cc = os.environ.get('CC') or next((c for c in ('cl.exe','clang-cl.exe','cc','clang','gcc') if shutil.which(c)), None)
assert cc and shutil.which(cc.split()[0]), 'no compiler on PATH; export CC=...'

try:
    compiler = find_compiler()
except RuntimeError:
    raise SystemExit('Install a C/C++ compiler or set CC/CXX before building libffi asm')

When it happens

Trigger: Raised when split_command(os.environ.get('CC'))/CXX don't yield a program that shutil.which() can find, AND none of cl.exe/cl/clang-cl.exe/clang-cl/cc/clang/gcc are on PATH.

Common situations: Minimal build containers without a compiler installed; PATH not inheriting the active compiler toolchain (common on Windows where CC isn't set and cl.exe lives behind a vcvarsall shell); CI images that install the compiler into a non-PATH location; cross-compile envs that forgot to export CC for the host.

Related errors

• Unable to locate armasm64.exe
• Preprocessing failed: {command}
• Unsupported libffi target {os_name}/{target_arch}.
• Missing libffi target header: {ffitarget_src}
• Unsupported host platform {sys.platform!r}

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/15217d811fb4c13d. Report an issue: GitHub.