53 lines · c
1// SPDX-License-Identifier: GPL-2.02/* Copyright (c) 2021, Oracle and/or its affiliates. */3 4#include "vmlinux.h"5 6#include <bpf/bpf_helpers.h>7#include <bpf/bpf_tracing.h>8#include <bpf/bpf_core_read.h>9 10char _license[] SEC("license") = "GPL";11 12unsigned int exception_triggered;13int test_pid;14 15/* TRACE_EVENT(task_newtask,16 * TP_PROTO(struct task_struct *p, u64 clone_flags)17 */18SEC("tp_btf/task_newtask")19int BPF_PROG(trace_task_newtask, struct task_struct *task, u64 clone_flags)20{21 int pid = bpf_get_current_pid_tgid() >> 32;22 struct callback_head *work;23 void *func;24 25 if (test_pid != pid)26 return 0;27 28 /* To verify we hit an exception we dereference task->task_works->func.29 * If task work has been added,30 * - task->task_works is non-NULL; and31 * - task->task_works->func is non-NULL also (the callback function32 * must be specified for the task work.33 *34 * However, for a newly-created task, task->task_works is NULLed,35 * so we know the exception handler triggered if task_works is36 * NULL and func is NULL.37 */38 work = task->task_works;39 func = work->func;40 /* Currently verifier will fail for `btf_ptr |= btf_ptr` * instruction.41 * To workaround the issue, use barrier_var() and rewrite as below to42 * prevent compiler from generating verifier-unfriendly code.43 */44 barrier_var(work);45 if (work)46 return 0;47 barrier_var(func);48 if (func)49 return 0;50 exception_triggered++;51 return 0;52}53