#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <limits.h>
#ifndef PAGESIZE
  #define PAGESIZE 4096
#endif

#include <sys/mman.h>


const unsigned char code[] = {
    0x55,               // push   %rbp
    0x48, 0x89, 0xe5,   // mov    %rsp,%rbp
    0x89, 0x7d, 0xfc,   // mov    %edi,-0x4(%rbp)
    0x89, 0x75, 0xf8,   // mov    %esi,-0x8(%rbp)
    0x8b, 0x55, 0xfc,   // mov    -0x4(%rbp),%edx
    0x8b, 0x45, 0xf8,   // mov    -0x8(%rbp),%eax
    0x01, 0xd0,         // add    %edx,%eax
    0x5d,               // pop    %rbp
    0xc3                // ret
};


struct _foo {
    unsigned char lpad[PAGESIZE - (2 << 6)];
    unsigned char code[sizeof(code)];
    unsigned char rpad[(2 << 6) - sizeof(code)];
} __attribute__((packed));


struct _foo foo;


int main(void)
{
    memcpy(foo.code, code, sizeof(code));
    size_t mask = PAGESIZE - 1;
    unsigned char *foo_p = (unsigned char *)(((long) &foo + mask) & ~mask);
    int (*f) (int, int) = (int (*) (int, int)) foo_p;
    int x = 2;
    int y = 2;

    if (mprotect(foo_p, sizeof(code), PROT_EXEC) < 0) {
        printf("%s\n", strerror(errno));
        return 1;
    }

    int z = f(x, y);
    printf("%d + %d = %d\n", x, y, z);
    return 0;
}