Win64_Thunking

// Thunking for
#if !_WIN64
#error "Windows x64-only""
#endif
#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <inttypes.h>

#include <windows.h>
#include <memoryapi.h>

#if HAS_STACK_ARGUMENTS
typedef int (*c_callback)(int one, int two, int three, int four, int five, int six);

int another(void* self, int one, int two, int three, int four, int five, int six) {
    printf("self = %p\n", self);
    printf("one = %d, two = %d, three = %d, four = %d, five = %d, six = %d\n", one, two , three, four, five, six);
    return one + two;
}

int function(int one, int two, int three, int four, void* self, const void* const __res, const void *const _dummy, int five, int six) {
    return another(self, one, two, three, four, five, six);
}
void call_callback(c_callback cb) {

    int ret = cb(1, 2, 3, 4, 5, 6);
    printf("ret = %d\n", ret);
}

#else
typedef int (*c_callback)(int one);
int another(void* self, int one) {
    printf("self = %p\n", self);
    printf("one = %d\n", one);
    return one + 2;
}
int function(int one, int _two, int _three, int _four, void* self, const void* const __res, const void* const _dummy) {
    return another(self, one);
}
void call_callback(c_callback cb) {
    int ret = cb(1);
    printf("ret = %d\n", ret);
}
#endif

int main()
{

    char* buffer = (char*)VirtualAlloc(NULL, 4096, MEM_COMMIT, PAGE_READWRITE);
    if (!buffer) {
        return -1;
    }
    uint64_t self = 42;

    int idx = 0;

    memcpy(buffer + idx, &self, 8);
    idx += 8;

    void* f_ptr = &function;
    memcpy(buffer + idx, &f_ptr, 8);
    idx += 8;

    unsigned char asm_command[] = {
        // _capture_ip:
          0x4C, 0x8D, 0x15, 0xF9, 0xFF, 0xFF, 0xFF, // lea         r10,[_capture_ip + 0FFFFFFF9h]
        // _push_return_address:
          0x4C, 0x8B, 0x1C, 0x24,                   // mov         r11,qword ptr [rsp]
          0x41, 0x53,                               // push        r11
          0x4C, 0x89, 0x5C, 0x24, 0x20,             // mov         qword ptr[rsp + 20h],r11
        // _push_self:
          0x41, 0x53,                               // push        r11
          0x4D, 0x8B, 0x5A, 0xF0,                   // mov         r11,qword ptr[r10 - 10h]
          0x4C, 0x89, 0x5C, 0x24, 0x20,             // mov         qword ptr[rsp + 20h],r11
         // _invoke:
          0x4D, 0x8B, 0x5A, 0xF8,                   // mov         r11,qword ptr[r10 - 8h]
          0x41, 0xFF, 0xD3,                         // call        r11
         // _restore_rsp:
          0x41, 0x5B,                               // pop         r11
          0x41, 0x5B,                               // pop         r11
          0x4C, 0x8B, 0x5C, 0x24, 0x18,             // mov         r11,qword ptr[rsp + 18h]
          0x4C, 0x89, 0x1C, 0x24,                   // mov         qword ptr[rsp],r11
          0xC3                                      // ret
    };
    memcpy(buffer + idx, asm_command, sizeof(asm_command));
    void* cmd_ptr = buffer + idx;

    DWORD _old_protect = 0;
    VirtualProtect(buffer, 1, PAGE_EXECUTE_READWRITE, &_old_protect);

    c_callback cb = (c_callback)(buffer + idx);
    call_callback(cb);

    VirtualFree(buffer, 0, MEM_RELEASE);

    printf("Goodbye\n");
}