1// SPDX-License-Identifier: GPL-2.0
2/*
3 * bpf-script-example.c
4 * Test basic LLVM building
5 */
6#ifndef LINUX_VERSION_CODE
7# error Need LINUX_VERSION_CODE
8# error Example: for 4.2 kernel, put 'clang-opt="-DLINUX_VERSION_CODE=0x40200" into llvm section of ~/.perfconfig'
9#endif
10#define BPF_ANY 0
11#define BPF_MAP_TYPE_ARRAY 2
12#define BPF_FUNC_map_lookup_elem 1
13#define BPF_FUNC_map_update_elem 2
14
15static void *(*bpf_map_lookup_elem)(void *map, void *key) =
16	(void *) BPF_FUNC_map_lookup_elem;
17static void *(*bpf_map_update_elem)(void *map, void *key, void *value, int flags) =
18	(void *) BPF_FUNC_map_update_elem;
19
20/*
21 * Following macros are taken from tools/lib/bpf/bpf_helpers.h,
22 * and are used to create BTF defined maps. It is easier to take
23 * 2 simple macros, than being able to include above header in
24 * runtime.
25 *
26 * __uint - defines integer attribute of BTF map definition,
27 * Such attributes are represented using a pointer to an array,
28 * in which dimensionality of array encodes specified integer
29 * value.
30 *
31 * __type - defines pointer variable with typeof(val) type for
32 * attributes like key or value, which will be defined by the
33 * size of the type.
34 */
35#define __uint(name, val) int (*name)[val]
36#define __type(name, val) typeof(val) *name
37
38#define SEC(NAME) __attribute__((section(NAME), used))
39struct {
40	__uint(type, BPF_MAP_TYPE_ARRAY);
41	__uint(max_entries, 1);
42	__type(key, int);
43	__type(value, int);
44} flip_table SEC(".maps");
45
46SEC("func=do_epoll_wait")
47int bpf_func__SyS_epoll_pwait(void *ctx)
48{
49	int ind =0;
50	int *flag = bpf_map_lookup_elem(&flip_table, &ind);
51	int new_flag;
52	if (!flag)
53		return 0;
54	/* flip flag and store back */
55	new_flag = !*flag;
56	bpf_map_update_elem(&flip_table, &ind, &new_flag, BPF_ANY);
57	return new_flag;
58}
59char _license[] SEC("license") = "GPL";
60int _version SEC("version") = LINUX_VERSION_CODE;
61