1 // SPDX-License-Identifier: GPL-2.0
2 // Copyright (c) 2019 Facebook
3 
4 #include <linux/ptrace.h>
5 #include <linux/bpf.h>
6 #include <bpf/bpf_helpers.h>
7 
8 static volatile const struct {
9 	unsigned a[4];
10 	/*
11 	 * if the struct's size is multiple of 16, compiler will put it into
12 	 * .rodata.cst16 section, which is not recognized by libbpf; work
13 	 * around this by ensuring we don't have 16-aligned struct
14 	 */
15 	char _y;
16 } rdonly_values = { .a = {2, 3, 4, 5} };
17 
18 static volatile struct {
19 	unsigned did_run;
20 	unsigned iters;
21 	unsigned sum;
22 } res;
23 
24 SEC("raw_tracepoint/sys_enter:skip_loop")
skip_loop(struct pt_regs * ctx)25 int skip_loop(struct pt_regs *ctx)
26 {
27 	/* prevent compiler to optimize everything out */
28 	unsigned * volatile p = (void *)&rdonly_values.a;
29 	unsigned iters = 0, sum = 0;
30 
31 	/* we should never enter this loop */
32 	while (*p & 1) {
33 		iters++;
34 		sum += *p;
35 		p++;
36 	}
37 	res.did_run = 1;
38 	res.iters = iters;
39 	res.sum = sum;
40 	return 0;
41 }
42 
43 SEC("raw_tracepoint/sys_enter:part_loop")
part_loop(struct pt_regs * ctx)44 int part_loop(struct pt_regs *ctx)
45 {
46 	/* prevent compiler to optimize everything out */
47 	unsigned * volatile p = (void *)&rdonly_values.a;
48 	unsigned iters = 0, sum = 0;
49 
50 	/* validate verifier can derive loop termination */
51 	while (*p < 5) {
52 		iters++;
53 		sum += *p;
54 		p++;
55 	}
56 	res.did_run = 1;
57 	res.iters = iters;
58 	res.sum = sum;
59 	return 0;
60 }
61 
62 SEC("raw_tracepoint/sys_enter:full_loop")
full_loop(struct pt_regs * ctx)63 int full_loop(struct pt_regs *ctx)
64 {
65 	/* prevent compiler to optimize everything out */
66 	unsigned * volatile p = (void *)&rdonly_values.a;
67 	int i = sizeof(rdonly_values.a) / sizeof(rdonly_values.a[0]);
68 	unsigned iters = 0, sum = 0;
69 
70 	/* validate verifier can allow full loop as well */
71 	while (i > 0 ) {
72 		iters++;
73 		sum += *p;
74 		p++;
75 		i--;
76 	}
77 	res.did_run = 1;
78 	res.iters = iters;
79 	res.sum = sum;
80 	return 0;
81 }
82 
83 char _license[] SEC("license") = "GPL";
84