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 #include <bpf/bpf_core_read.h>
8 #include "bpf_misc.h"
9
10 /* weak and shared between two files */
11 const volatile __u32 my_tid __weak;
12 long syscall_id __weak;
13
14 int output_val1;
15 int output_ctx1;
16 int output_weak1;
17
18 /* same "subprog" name in all files, but it's ok because they all are static */
19 static __noinline int subprog(int x)
20 {
21 /* but different formula */
22 return x * 1;
23 }
24
25 /* Global functions can't be void */
26 int set_output_val1(int x)
27 {
28 output_val1 = x + subprog(x);
29 return x;
30 }
31
32 /* This function can't be verified as global, as it assumes raw_tp/sys_enter
33 * context and accesses syscall id (second argument). So we mark it as
34 * __hidden, so that libbpf will mark it as static in the final object file,
35 * right before verifying it in the kernel.
36 *
37 * But we don't mark it as __hidden here, rather at extern site. __hidden is
38 * "contaminating" visibility, so it will get propagated from either extern or
39 * actual definition (including from the losing __weak definition).
40 */
41 void set_output_ctx1(__u64 *ctx)
42 {
43 output_ctx1 = ctx[1]; /* long id, same as in BPF_PROG below */
44 }
45
46 /* this weak instance should win because it's the first one */
47 __weak int set_output_weak(int x)
48 {
49 static volatile int whatever;
50
51 /* make sure we use CO-RE relocations in a weak function, this used to
52 * cause problems for BPF static linker
53 */
54 whatever = bpf_core_type_size(struct task_struct);
55 __sink(whatever);
56
57 output_weak1 = x;
58 return x;
59 }
60
61 extern int set_output_val2(int x);
62
63 /* here we'll force set_output_ctx2() to be __hidden in the final obj file */
64 __hidden extern void set_output_ctx2(__u64 *ctx);
65
66 SEC("?raw_tp/sys_enter")
67 int BPF_PROG(handler1, struct pt_regs *regs, long id)
68 {
69 static volatile int whatever;
70
71 if (my_tid != (u32)bpf_get_current_pid_tgid() || id != syscall_id)
72 return 0;
73
74 /* make sure we have CO-RE relocations in main program */
75 whatever = bpf_core_type_size(struct task_struct);
76 __sink(whatever);
77
78 set_output_val2(1000);
79 set_output_ctx2(ctx); /* ctx definition is hidden in BPF_PROG macro */
80
81 /* keep input value the same across both files to avoid dependency on
82 * handler call order; differentiate by output_weak1 vs output_weak2.
83 */
84 set_output_weak(42);
85
86 return 0;
87 }
88
89 char LICENSE[] SEC("license") = "GPL";
90
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