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