// SPDX-License-Identifier: GPL-2.0
// Copyright (c) 2018 Facebook

#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>

#ifndef PERF_MAX_STACK_DEPTH
#define PERF_MAX_STACK_DEPTH         127
#endif

struct {
        __uint(type, BPF_MAP_TYPE_ARRAY);
        __uint(max_entries, 1);
        __type(key, __u32);
        __type(value, __u32);
} control_map SEC(".maps");

struct {
        __uint(type, BPF_MAP_TYPE_HASH);
        __uint(max_entries, 16384);
        __type(key, __u32);
        __type(value, __u32);
} stackid_hmap SEC(".maps");

typedef struct bpf_stack_build_id stack_trace_t[PERF_MAX_STACK_DEPTH];

struct {
        __uint(type, BPF_MAP_TYPE_STACK_TRACE);
        __uint(max_entries, 128);
        __uint(map_flags, BPF_F_STACK_BUILD_ID);
        __type(key, __u32);
        __type(value, stack_trace_t);
} stackmap SEC(".maps");

struct {
        __uint(type, BPF_MAP_TYPE_ARRAY);
        __uint(max_entries, 128);
        __type(key, __u32);
        __type(value, stack_trace_t);
} stack_amap SEC(".maps");

SEC("kprobe/urandom_read_iter")
int oncpu(struct pt_regs *args)
{
        __u32 max_len = sizeof(struct bpf_stack_build_id)
                        * PERF_MAX_STACK_DEPTH;
        __u32 key = 0, val = 0, *value_p;
        void *stack_p;

        value_p = bpf_map_lookup_elem(&control_map, &key);
        if (value_p && *value_p)
                return 0; /* skip if non-zero *value_p */

        /* The size of stackmap and stackid_hmap should be the same */
        key = bpf_get_stackid(args, &stackmap, BPF_F_USER_STACK);
        if ((int)key >= 0) {
                bpf_map_update_elem(&stackid_hmap, &key, &val, 0);
                stack_p = bpf_map_lookup_elem(&stack_amap, &key);
                if (stack_p)
                        bpf_get_stack(args, stack_p, max_len,
                                      BPF_F_USER_STACK | BPF_F_USER_BUILD_ID);
        }

        return 0;
}

char _license[] SEC("license") = "GPL";