Put a shared object into a specific virtual address and execute - c

Question

I would like to do the following: I have a function in a .c file. I want to compile it, then in my main function, I want to put this object to a certain virtual address.
This is my shared function in sharedfunction.c
#include <stdio.h>
int dummy;
void sharedfunction(int x){
if(x){
dummy &= x;
}
}
I have compiled it using:
gcc -c -fPIC sharedfunction.c -o sharedfunction.o
Now, I would like to put this object to a certain virtual address in my main function.
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define pagesize 4096UL
#define handle_error(msg) \
do { perror(msg); exit(EXIT_FAILURE); } while (0)
int main() {
void *p = main;
printf("main:%p\n", p);
int fd;
struct stat sb;
off_t offset, pa_offset;
fd = open("sharedfunction.o", O_RDONLY);
if(fd == -1)
handle_error("open");
if (fstat(fd, &sb) == -1) /* To obtain file size */
handle_error("fstat");
offset = 0;
pa_offset = offset & ~(sysconf(_SC_PAGE_SIZE) - 1);
/* offset for mmap() must be page aligned */
if (offset >= sb.st_size) {
fprintf(stderr, "offset is past end of file\n");
exit(EXIT_FAILURE);
}
// want to put main + 0x10_000 virtual address
void* func = mmap(
(void*) (p + 0x10000),
pagesize,
PROT_READ|PROT_WRITE|PROT_EXEC,
MAP_PRIVATE,
fd, pa_offset);
if (func == MAP_FAILED)
handle_error("mmap");
// how can I call this?
func(10);
return 0;
}
I am compiling with:
gcc -O0 main.c -o main.o
How can I call the func?
How can I clear the memory after I am finished with that func?