nodejs/node · error · RuntimeError

Assembly failed: {asm_command}

Error message

Assembly failed: {asm_command}

What it means

After preprocessing, if --assemble was requested, preprocess_asm.py invokes armasm64.exe to turn the cleaned .s text into a .obj. If armasm64 exits non-zero the script logs both stderr and stdout and raises RuntimeError with the assembler command, rather than writing a half-assembled object file.

Source

Thrown at deps/libffi/preprocess_asm.py:117

    lines = result.stdout.splitlines(keepends=True)
    cleaned_lines = [line for line in lines if not line.lstrip().startswith('#')]
    cleaned = ''.join(cleaned_lines)

    output.write_text(cleaned, encoding='utf-8')

    # If --assemble is specified, also run the assembler to produce an object file
    if args.assemble:
        assemble_output = Path(normalize_path(args.assemble))
        assemble_output.parent.mkdir(parents=True, exist_ok=True)

        armasm64 = find_armasm64()
        asm_command = [armasm64, '-nologo', '-g', str(output), '-o', str(assemble_output)]

        asm_result = subprocess.run(asm_command, capture_output=True, text=True)
        if asm_result.returncode != 0:
            sys.stderr.write(asm_result.stderr)
            sys.stderr.write(asm_result.stdout)
            raise RuntimeError(f'Assembly failed: {" ".join(asm_command)}')


def main(argv=None):
    parser = argparse.ArgumentParser(description='Preprocess libffi assembly source')
    parser.add_argument('--input', required=True)
    parser.add_argument('--output', required=True)
    parser.add_argument('--include-dir', action='append', default=[])
    parser.add_argument('--define', action='append', default=[])
    parser.add_argument('--assemble', help='Also assemble the output to this object file')
    args = parser.parse_args(argv)

    preprocess(args)
    return 0


if __name__ == '__main__':
    raise SystemExit(main())

View on GitHub (pinned to 1b2de5e052)

Solutions

1. Inspect the armasm64 stderr/stdout the script already wrote to find the offending line/instruction.
2. Verify the preprocessed output (the --output file) is clean ARM assembly with no stray C directives.
3. Match the armasm64 version to the ARM ISA the source targets (e.g. ARMv8.3 vs v8.0).

Example fix

# before: preprocessed output still has stray # line markers
python preprocess_asm.py --input src.S --output out.s --assemble out.obj
# after: regenerate clean preprocessed file, then assemble
python preprocess_asm.py --input src.S --output out.s --include-dir include --assemble out.obj

asm_result = subprocess.run(asm_command, capture_output=True, text=True)
if asm_result.returncode != 0:
    raise SystemExit(f'armasm64 failed:\n{asm_result.stderr}{asm_result.stdout}')

try:
    preprocess(args)
except RuntimeError as e:
    raise SystemExit(f'libffi assembly failed: {e}') from None

When it happens

Trigger: Raised when `subprocess.run(asm_command, ...).returncode != 0` in the `if args.assemble:` branch. asm_command is [armasm64, '-nologo', '-g', <preprocessed file>, '-o', <object file>].

Common situations: Preprocessor left a directive armasm64 can't parse (stripping of '#' lines was incomplete); ARM syntax the toolchain version doesn't accept; wrong ARM toolchain major version; source file targets a different ARM ISA than the installed armasm64.

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/96b8ca95052f084a. Report an issue: GitHub.