Load/Run-time Interposition: fixing segmentation fault

there is some codes in the system programming lecture metarial for load time interposition.

The code of mymalloc.c belows.

#ifdef RUNTIME
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>

void _malloc(size_t size)  
{  
    void *(_mallocp) (size_t size) = NULL;


    mallocp = dlsym(RTLD_NEXT, "malloc");
    if(!mallocp) {
        fputs(dlerror(), stderr);
        exit(1);
    }

    void *ptr = mallocp(size);

    printf("malloc(%d): %p\n", (int) size, ptr);
    return ptr;
}  
#endif

The code of int.c belows.

#include<stdio.h>  
#include<malloc.h>

int main() {
    int *p = malloc(32);
    free(p);
    return 0;
}

I compiled the souce code mymalloc.c
with gcc -Wall -DRUNTIME -shared -fpic -o mymalloc.so mymalloc..c -ldl,
and int.c
with gcc -Wall -o intr int.c.

but the result of LD_PRELOAD="./mymalloc.so" ./intr was segmentation fault.
The reason was that printf() uses malloc function itself, so the shared object causes infinite recursion.
I can fix the sigsegv error by replacing printf("malloc(%d): %p\n", (int) size, ptr); to

char str_buf[256] = {0};
sprintf(str_buf, "malloc(%d): %p\n", (int) size, ptr);
write(1, str_buf, strlen(str_buf));

reference: https://stackoverflow.com/questions/22196097/ld-preload-causing-segmentation-fault-for-linux-commands