1 // SPDX-License-Identifier: GPL-2.0
2 /* Copyright (c) 2021 Facebook */
3 
4 #include "vmlinux.h"
5 #include <bpf/bpf_helpers.h>
6 #include <bpf/bpf_tracing.h>
7 
8 /* weak and shared between two files */
9 const volatile int my_tid __weak;
10 long syscall_id __weak;
11 
12 int output_val1;
13 int output_ctx1;
14 int output_weak1;
15 
16 /* same "subprog" name in all files, but it's ok because they all are static */
17 static __noinline int subprog(int x)
18 {
19 	/* but different formula */
20 	return x * 1;
21 }
22 
23 /* Global functions can't be void */
24 int set_output_val1(int x)
25 {
26 	output_val1 = x + subprog(x);
27 	return x;
28 }
29 
30 /* This function can't be verified as global, as it assumes raw_tp/sys_enter
31  * context and accesses syscall id (second argument). So we mark it as
32  * __hidden, so that libbpf will mark it as static in the final object file,
33  * right before verifying it in the kernel.
34  *
35  * But we don't mark it as __hidden here, rather at extern site. __hidden is
36  * "contaminating" visibility, so it will get propagated from either extern or
37  * actual definition (including from the losing __weak definition).
38  */
39 void set_output_ctx1(__u64 *ctx)
40 {
41 	output_ctx1 = ctx[1]; /* long id, same as in BPF_PROG below */
42 }
43 
44 /* this weak instance should win because it's the first one */
45 __weak int set_output_weak(int x)
46 {
47 	output_weak1 = x;
48 	return x;
49 }
50 
51 extern int set_output_val2(int x);
52 
53 /* here we'll force set_output_ctx2() to be __hidden in the final obj file */
54 __hidden extern void set_output_ctx2(__u64 *ctx);
55 
56 SEC("raw_tp/sys_enter")
57 int BPF_PROG(handler1, struct pt_regs *regs, long id)
58 {
59 	if (my_tid != (u32)bpf_get_current_pid_tgid() || id != syscall_id)
60 		return 0;
61 
62 	set_output_val2(1000);
63 	set_output_ctx2(ctx); /* ctx definition is hidden in BPF_PROG macro */
64 
65 	/* keep input value the same across both files to avoid dependency on
66 	 * handler call order; differentiate by output_weak1 vs output_weak2.
67 	 */
68 	set_output_weak(42);
69 
70 	return 0;
71 }
72 
73 char LICENSE[] SEC("license") = "GPL";
74