raw_tp_null.c

 1// SPDX-License-Identifier: GPL-2.0
 2/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
 3
 4#include <vmlinux.h>
 5#include <bpf/bpf_tracing.h>
 6#include "bpf_misc.h"
 7
 8char _license[] SEC("license") = "GPL";
 9
10int tid;
11int i;
12
13SEC("tp_btf/bpf_testmod_test_raw_tp_null_tp")
14int BPF_PROG(test_raw_tp_null, struct sk_buff *skb)
15{
16	struct task_struct *task = bpf_get_current_task_btf();
17
18	if (task->pid != tid)
19		return 0;
20
21	/* If dead code elimination kicks in, the increment +=2 will be
22	 * removed. For raw_tp programs attaching to tracepoints in kernel
23	 * modules, we mark input arguments as PTR_MAYBE_NULL, so branch
24	 * prediction should never kick in.
25	 */
26	asm volatile ("%[i] += 1; if %[ctx] != 0 goto +1; %[i] += 2;"
27			: [i]"+r"(i)
28			: [ctx]"r"(skb)
29			: "memory");
30	return 0;
31}