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 int 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