printf is producing the segmentation fault? - multithreading

Question

I'm learning threads and my code runs upto last print statement. Why it is giving segmentation fault at print? I think possible reason could be non-existant address passed as argument to print, but it is not the reason, I'm passing valid address.
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
void *thread (void *vargp) {
int arg = *((int*)vargp);
return &arg;
}
int main () {
pthread_t tid;
int thread_arg = 0x7ffdbc32fa34;
int *ret_value;
pthread_create(&tid, NULL, thread, &thread_arg);
pthread_join(tid, (void **)(&ret_value));
printf("hello\n");
printf("%X\n", *ret_value);
return 0;
}
It is giving following output:
hello
Segmentation fault (core dumped)
Is it because I'm returning an address of a local variable, which gets destroyed once thread is returned? I don't think so, because changing to following code is also giving me segmentation fault!
void *thread (void *vargp) {
int * arg = malloc(sizeof(int));
*arg = *((int*)vargp);
return &arg;
}

Answer 1

Is it because I'm returning an address of a local variable, which gets
destroyed once thread is returned?
Yes, it is.
I don't think so, because changing to following code is also giving me
segmentation fault!
This code is also returning the address of a local variable (return &arg;). Instead, you should be returning the pointer value that malloc() returned (return arg;):
void *thread (void *vargp)
{
int * arg = malloc(sizeof(int));
*arg = *((int*)vargp);
return arg;
}
You also should not be casting the address of ret_value to type void ** in main() - the variable is of type int * not void *, so it shouldn't be written to through a void ** pointer (although, in practice, this will usually work). Instead, you should be using void * variable to hold the return value, then either casting this value to int * or assigning it to a variable of type int *:
void *ret_value;
pthread_create(&tid, NULL, thread, &thread_arg);
pthread_join(tid, &ret_value);
printf("%X\n", *(int *)ret_value);