#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include <stdint.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/syscall.h>

static inline int sys_bpf(enum bpf_cmd cmd, union bpf_attr *attr,
              unsigned int size)
{
    return syscall(__NR_bpf, cmd, attr, size);
}

int bpf_create_map(enum bpf_map_type map_type,
           unsigned int key_size,
           unsigned int value_size,
           unsigned int max_entries)
{
    union bpf_attr attr = {
      .map_type    = map_type,
      .key_size    = key_size,
      .value_size  = value_size,
      .max_entries = max_entries
    };

    return sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
}

SEC("ksyscall/execve")

int hello(void *ctx) {
    int counter_table, key, value;
    counter_table = bpf_create_map(BPF_MAP_TYPE_HASH, sizeof(key), sizeof(value), 10240);
    uint64_t uid;
    uint64_t counter = 0;
    uint64_t *p;

    uid = bpf_get_current_uid_gid() & 0xFFFFFFFF;   //returns a 64 bits integer containing the current GID and UID
                                                    //gets the user id that is running the process that trigegered this krpobe event. 
                                                    //user-id is held in lowest 32 bits of the 64-bit value that gets returned. (top 32 holds the group id)
    p = bpf_map_lookup_elem(&counter_table, (&uid)); //returns a pointer to the corresponding value in the hash table 
    if (p!= 0) {
        counter = *p;
    }

    counter++;
    bpf_map_update_elem(&counter_table, &uid, &counter, 0);
    return 0;
}

I have this simple program where I am learning how to use BPF commands to create maps and investigate further within the map. It compiles without any error using Clang, but when I try to load it using the bpftool, it throws following error.

libbpf: failed to find BTF for extern 'syscall' [8] section: -2
Error: failed to open object file

Could someone help me to understand this error and how to fix it?