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 */
subprog(int x)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 */
set_output_val1(int x)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 */
set_output_ctx1(__u64 * ctx)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 */
set_output_weak(int x)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")
BPF_PROG(handler1,struct pt_regs * regs,long id)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