Very small JIT with constant program

main.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#ifdef _WIN32
#include "mman.h"
#else
#include <sys\mman>
#endif

// This simple JIT program just returns the user input number
int dyn_program1(const char *user_input)
{
    //  mov eax, 0x0
    //  ret
    unsigned char program[]
        = { 0xb8    // -  mov eax
          , 0x00    //
          , 0x00    //
          , 0x00    //
          , 0x00    // -  0x0       // We will change this value by the input value:  program[4] = user value
          , 0xc3 }; // -  ret

    // Assign the user value to the program
    const int input_num = atoi(user_input);
    memcpy(&program[1], &input_num, 4);

    // Defining the dynamic memory that our mini JIT program will take up
    void *lptr = mmap(NULL, sizeof(program)
        , PROT_WRITE
        | PROT_EXEC
        , MAP_ANON
        | MAP_PRIVATE, -1, 0);
    // Injecting our mini program dynamically into the memory
    memcpy(lptr, program, sizeof(program));

    // This define the pointer to call the mini program
    const int (*dyn_func)() = lptr;
    // Calling this function pointer will make execute our mini program
    // `call_res` will handle the return value, in this case, this will be
    // the value entered by the user.
    const int call_res = dyn_func();

    // We no longer need our mini dynamic JIT program
    // Se we free the memory used
    munmap(lptr, sizeof(program));

    // Display some info
    printf("You entered '%s' and the JIT function returned '%d'.\n", user_input, call_res);
    return call_res;
}

// This simple JIT program just returns the user input number multiplied by 10
int dyn_program2(const char *user_input)
{
    // mov eax, 0
    // imul eax, 10
    // ret
    unsigned char program[]
        = { 0xb8    // -  mov eax
          , 0x00
          , 0x00
          , 0x00
          , 0x00    // -  0x0       // We will change this value by the input value:  program[4] = user value
          , 0x6b    // -  imul eax, eax, 0xa
          , 0xc0
          , 0x0a
          , 0xc3 }; // -  ret

    // Assign the user value to the program
    const int input_num = atoi(user_input);
    memcpy(&program[1], &input_num, 4);

    // Defining the dynamic memory that our mini JIT program will take up
    void *lptr = mmap(NULL, sizeof(program)
        , PROT_WRITE
        | PROT_EXEC
        , MAP_ANON
        | MAP_PRIVATE, -1, 0);
    // Injecting our mini program dynamically into the memory
    memcpy(lptr, program, sizeof(program));

    // This define the pointer to call the mini program
    const int (*dyn_func)() = lptr;
    // Calling this function pointer will make execute our mini program
    // `call_res` will handle the return value, in this case, this will be
    // the value entered by the user.
    const int call_res = dyn_func();

    // We no longer need our mini dynamic JIT program
    // Se we free the memory used
    munmap(lptr, sizeof(program));

    // Display some info
    printf("You entered '%s' and the JIT function returned '%d'.\n", user_input, call_res);
    return call_res;
}

int main(int argc, char *argv[])
{
    // The usage of this mini program
    if (argc < 2)
        return fprintf(stderr, "Usage: main <number>\n"), EXIT_FAILURE;
    
    const int res0 = dyn_program1(argv[1]);
    const int res1 = dyn_program2(argv[1]);

    return EXIT_SUCCESS;
}

mman.h

/*
 * sys/mman.h
 * mman-win32
 */

#pragma once

#ifndef _WIN32_WINNT        // Allow use of features specific to Windows XP or later.
#define _WIN32_WINNT 0x0501 // Change this to the appropriate value to target other versions of Windows.
#endif

/* All the headers include this file. */
#ifndef _MSC_VER
#include <_mingw.h>
#endif

#include <sys/types.h>

#ifdef __cplusplus
extern "C"
{
#endif

#define PROT_NONE 0
#define PROT_READ 1
#define PROT_WRITE 2
#define PROT_EXEC 4

#define MAP_FILE 0
#define MAP_SHARED 1
#define MAP_PRIVATE 2
#define MAP_TYPE 0xf
#define MAP_FIXED 0x10
#define MAP_ANONYMOUS 0x20
#define MAP_ANON MAP_ANONYMOUS

#define MAP_FAILED ((void *)-1)

/* Flags for msync. */
#define MS_ASYNC 1
#define MS_SYNC 2
#define MS_INVALIDATE 4

    void *mmap(void *addr, size_t len, int prot, int flags, int fildes, off_t off);
    int munmap(void *addr, size_t len);
    int mprotect(void *addr, size_t len, int prot);
    int msync(void *addr, size_t len, int flags);
    int mlock(const void *addr, size_t len);
    int munlock(const void *addr, size_t len);

#ifdef __cplusplus
};
#endif

#include <windows.h>
#include <errno.h>
#include <io.h>

#ifndef FILE_MAP_EXECUTE
#define FILE_MAP_EXECUTE 0x0020
#endif /* FILE_MAP_EXECUTE */

static int __map_mman_error(const DWORD err, const int deferr)
{
    if (err == 0)
        return 0;
    //TODO: implement
    return err;
}

static DWORD __map_mmap_prot_page(const int prot)
{
    DWORD protect = 0;

    if (prot == PROT_NONE)
        return protect;

    if ((prot & PROT_EXEC) != 0)
    {
        protect = ((prot & PROT_WRITE) != 0) ? PAGE_EXECUTE_READWRITE : PAGE_EXECUTE_READ;
    }
    else
    {
        protect = ((prot & PROT_WRITE) != 0) ? PAGE_READWRITE : PAGE_READONLY;
    }

    return protect;
}

static DWORD __map_mmap_prot_file(const int prot)
{
    DWORD desiredAccess = 0;

    if (prot == PROT_NONE)
        return desiredAccess;

    if ((prot & PROT_READ) != 0)
        desiredAccess |= FILE_MAP_READ;
    if ((prot & PROT_WRITE) != 0)
        desiredAccess |= FILE_MAP_WRITE;
    if ((prot & PROT_EXEC) != 0)
        desiredAccess |= FILE_MAP_EXECUTE;

    return desiredAccess;
}

inline void *mmap(void *addr, size_t len, int prot, int flags, int fildes, off_t off)
{
    HANDLE fm, h;

    void *map = MAP_FAILED;

#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable : 4293)
#endif

    const DWORD dwFileOffsetLow = (sizeof(off_t) <= sizeof(DWORD)) ? (DWORD)off : (DWORD)(off & 0xFFFFFFFFL);
    const DWORD dwFileOffsetHigh = (sizeof(off_t) <= sizeof(DWORD)) ? (DWORD)0 : (DWORD)((off >> 32) & 0xFFFFFFFFL);
    const DWORD protect = __map_mmap_prot_page(prot);
    const DWORD desiredAccess = __map_mmap_prot_file(prot);

    const off_t maxSize = off + (off_t)len;

    const DWORD dwMaxSizeLow = (sizeof(off_t) <= sizeof(DWORD)) ? (DWORD)maxSize : (DWORD)(maxSize & 0xFFFFFFFFL);
    const DWORD dwMaxSizeHigh = (sizeof(off_t) <= sizeof(DWORD)) ? (DWORD)0 : (DWORD)((maxSize >> 32) & 0xFFFFFFFFL);

#ifdef _MSC_VER
#pragma warning(pop)
#endif

    errno = 0;

    if (len == 0
        /* Unsupported flag combinations */
        || (flags & MAP_FIXED) != 0
        /* Usupported protection combinations */
        || prot == PROT_EXEC)
    {
        errno = EINVAL;
        return MAP_FAILED;
    }

    h = ((flags & MAP_ANONYMOUS) == 0) ? (HANDLE)_get_osfhandle(fildes) : INVALID_HANDLE_VALUE;

    if ((flags & MAP_ANONYMOUS) == 0 && h == INVALID_HANDLE_VALUE)
    {
        errno = EBADF;
        return MAP_FAILED;
    }

    fm = CreateFileMapping(h, NULL, protect, dwMaxSizeHigh, dwMaxSizeLow, NULL);

    if (fm == NULL)
    {
        errno = __map_mman_error(GetLastError(), EPERM);
        return MAP_FAILED;
    }

    map = MapViewOfFile(fm, desiredAccess, dwFileOffsetHigh, dwFileOffsetLow, len);

    CloseHandle(fm);

    if (map == NULL)
    {
        errno = __map_mman_error(GetLastError(), EPERM);
        return MAP_FAILED;
    }

    return map;
}

inline int munmap(void *addr, size_t len)
{
    if (UnmapViewOfFile(addr))
        return 0;

    errno = __map_mman_error(GetLastError(), EPERM);

    return -1;
}

inline int mprotect(void *addr, size_t len, int prot)
{
    DWORD newProtect = __map_mmap_prot_page(prot);
    DWORD oldProtect = 0;

    if (VirtualProtect(addr, len, newProtect, &oldProtect))
        return 0;

    errno = __map_mman_error(GetLastError(), EPERM);

    return -1;
}

inline int msync(void *addr, size_t len, int flags)
{
    if (FlushViewOfFile(addr, len))
        return 0;

    errno = __map_mman_error(GetLastError(), EPERM);

    return -1;
}

inline int mlock(const void *addr, size_t len)
{
    if (VirtualLock((LPVOID)addr, len))
        return 0;

    errno = __map_mman_error(GetLastError(), EPERM);

    return -1;
}

inline int munlock(const void *addr, size_t len)
{
    if (VirtualUnlock((LPVOID)addr, len))
        return 0;

    errno = __map_mman_error(GetLastError(), EPERM);

    return -1;
}

Example of result:

./main 6
You entered '6' and the JIT function returned '6'.
You entered '6' and the JIT function returned '60'.