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If someone want to test on Linux the code from the first post in this thread, use mmap() instead of malloc(), here the working code (Ubuntu 20.04 64 bit) compiled with -m32 (it's fundamental!!!) flag:

// Include the prototypes of the functions we are using...
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>

/* In the beginning we'll have to define the function pointer.
* I called the function 'dyncode' and gave it an int argument
* as well as an int return value just to show what's possible.

int (*dyncode)(int); // prototype for call of dynamic code

/* The following char array is initialized with some binary code
* which takes the first argument from the stack, increases it,
* and returns to the caller.
* Just very simple code for testing purposes...

unsigned char code[] = {0x8B,0x44,0x24,0x04,  // mov eax, [esp+4]
                        0x40,                 // inc eax
                        0xC3                  // ret

int main(void)
    /* To show you that the code can be dynamically generated
     * although I defined static data above, the code is copied
     * into an allocated memory area and the starting address is
     * assigned to the function pointer 'dyncode'.
     * The strange stuff in front of the malloc is just to cast
     * the address to the same format the function pointer is
     * defined with, otherwise you'd get a compiler warning.

    dyncode = mmap(NULL, sizeof(code), PROT_READ | PROT_WRITE | PROT_EXEC, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
    memcpy(dyncode, code, sizeof(code));

    /* To show that the code works it is called with the argument 41
     * and the return value sould be 42, obviously.

    printf("Return value = %d\n", (*dyncode)(41) ); // call the code and print the return value

    munmap(dyncode, sizeof(code));

    return 0;
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