Writing Tiny Executables in C

crt.c

/**
    Compile with your C console project.
*/
#include <stdio.h>
#include <windows.h>

#define __UNKNOWN_APP    0
#define __CONSOLE_APP    1
#define __GUI_APP        2

int main(int, char **, char **);
int wmain(int, wchar_t **, wchar_t **);

typedef void (__cdecl * new_handler) ();

typedef struct _startupinfo_t {
    int newmode;
    new_handler newh;
} _startupinfo;

int __getmainargs(int *argc, char ***argv, char ***penv, int glob, _startupinfo *info);
int __wgetmainargs(int *argc, wchar_t ***argv, wchar_t ***penv, int glob, _startupinfo *info);

#ifndef _UNICODE
    void mainCRTStartup(void)
#else
    void wmainCRTStartup(void)
#endif
{
    _startupinfo si = {0};
    int argc, ret;
    
    __set_app_type(__CONSOLE_APP);
    
    #ifndef _UNICODE
        char **argv = NULL;
        char **envp = NULL;
        
        __getmainargs(&argc, &argv, &envp, 0, &si);
        ret = main(argc, argv, envp);
    #else
        wchar_t **argv = NULL;
        wchar_t **wenvp = NULL;
        
        __wgetmainargs(&argc, &wargv, &wenvp, 0, &si);
        ret = wmain(argc, wargv, wenvp);
    #endif

    ExitProcess(ret);
}

dll2def.py

#!/usr/bin/env python3
"""
dll2def.py - Create a module-definition (.def) file from a Windows DLL.

Usage
-----
    python dll2def.py library.dll  [optional_output.def]

The script writes a .def file next to the DLL (or to the explicitly
supplied output path) and prints a short summary.

Requires
--------
    pip install pefile
"""
from __future__ import annotations
import argparse
import sys
from pathlib import Path
import pefile


def build_def_text(dll_path: Path) -> str:
    """Return the complete .def file text for *dll_path*."""
    pe = pefile.PE(dll_path.as_posix(), fast_load=True)
    pe.parse_data_directories(directories=[pefile.DIRECTORY_ENTRY['IMAGE_DIRECTORY_ENTRY_EXPORT']])

    if not hasattr(pe, 'DIRECTORY_ENTRY_EXPORT'):
        raise ValueError(f"'{dll_path.name}' has no export table.")

    lines: list[str] = []
    lines.append(f'LIBRARY "{dll_path.name}"')
    lines.append('EXPORTS')

    for sym in pe.DIRECTORY_ENTRY_EXPORT.symbols:
        # Symbol names can be None (export-by-ordinal only)
        name = sym.name.decode(errors='replace') if sym.name else f'#{sym.ordinal}'
        lines.append(f'    {name}')

    # A final newline keeps MSVC's LIB.EXE happy
    return '\n'.join(lines) + '\n'


def parse_args(argv: list[str]) -> argparse.Namespace:
    p = argparse.ArgumentParser(description="Generate a .def file from a DLL's export table.")
    p.add_argument('dll', type=Path, help='Path to the input DLL')
    p.add_argument('out', nargs='?', type=Path,
                   help='Optional .def output path (default: DLL name with .def extension)')
    return p.parse_args(argv)


def main(argv: list[str] | None = None) -> None:
    args = parse_args(argv or sys.argv[1:])

    dll_path: Path = args.dll.expanduser().resolve()
    if not dll_path.is_file():
        sys.exit(f"Error: '{dll_path}' is not a file.")

    out_path: Path = (args.out or dll_path.with_suffix('.def')).expanduser().resolve()

    try:
        def_text = build_def_text(dll_path)
    except Exception as exc:
        sys.exit(f"Failed to read exports: {exc}")

    out_path.write_text(def_text, encoding='utf-8')
    print(f"Wrote {out_path} ({len(def_text.splitlines()) - 2} exports)")


if __name__ == '__main__':
    main()

hello.c

// cl /D_NO_CRT_STDIO_INLINE /Os /O1 /GS- hello.c crt.c /link /nodefaultlib /subsystem:console msvcrt.lib kernel32.lib

#include <stdio.h>

int main(int argc, char *argv[]) {
    for (int i=0; i<argc; i++) {
        printf("argv[%i]: %s\n", i, argv[i]);
    }
    return 0;
}