test.c

#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <unistd.h>
#include <string.h>

/* 00000000004004b6 <pass1>: */
/*   4004b6:       55                      push   %rbp */
/*   4004b7:       48 89 e5                mov    %rsp,%rbp */
/*   4004ba:       89 7d fc                mov    %edi,-0x4(%rbp) */
/*   4004bd:       8b 45 fc                mov    -0x4(%rbp),%eax */
/*   4004c0:       83 c0 01                add    $0x1,%eax */
/*   4004c3:       5d                      pop    %rbp */
/*   4004c4:       c3                      retq    */

int pass1(int x) {
    return (x + 1);
}

int main() {

    uint8_t pass1a[] = {
        0x55, 0x48, 0x89, 0xe5, 0x89, 0x7d, 0xfc, 0x8b,
        0x45, 0xfc, 0x83, 0xc0, 0x01, 0x5d, 0xc3
    };

    size_t pagesize = sysconf(_SC_PAGESIZE);
    int (*pass1b)(int) = aligned_alloc(pagesize, pagesize);

    memcpy(pass1b, pass1a, sizeof pass1a);
    
    if (mprotect(pass1b, sizeof pass1b, PROT_EXEC) != 0) {
        perror("mprotect failed:");
        return -1;
    }

    return pass1b(123);
}