--- /dev/null
+/*
+ * Tracing hooks
+ *
+ * Copyright (C) 2008-2009 Red Hat, Inc. All rights reserved.
+ *
+ * This copyrighted material is made available to anyone wishing to use,
+ * modify, copy, or redistribute it subject to the terms and conditions
+ * of the GNU General Public License v.2.
+ *
+ * This file defines hook entry points called by core code where
+ * user tracing/debugging support might need to do something. These
+ * entry points are called tracehook_*(). Each hook declared below
+ * has a detailed kerneldoc comment giving the context (locking et
+ * al) from which it is called, and the meaning of its return value.
+ *
+ * Each function here typically has only one call site, so it is ok
+ * to have some nontrivial tracehook_*() inlines. In all cases, the
+ * fast path when no tracing is enabled should be very short.
+ *
+ * The purpose of this file and the tracehook_* layer is to consolidate
+ * the interface that the kernel core and arch code uses to enable any
+ * user debugging or tracing facility (such as ptrace). The interfaces
+ * here are carefully documented so that maintainers of core and arch
+ * code do not need to think about the implementation details of the
+ * tracing facilities. Likewise, maintainers of the tracing code do not
+ * need to understand all the calling core or arch code in detail, just
+ * documented circumstances of each call, such as locking conditions.
+ *
+ * If the calling core code changes so that locking is different, then
+ * it is ok to change the interface documented here. The maintainer of
+ * core code changing should notify the maintainers of the tracing code
+ * that they need to work out the change.
+ *
+ * Some tracehook_*() inlines take arguments that the current tracing
+ * implementations might not necessarily use. These function signatures
+ * are chosen to pass in all the information that is on hand in the
+ * caller and might conceivably be relevant to a tracer, so that the
+ * core code won't have to be updated when tracing adds more features.
+ * If a call site changes so that some of those parameters are no longer
+ * already on hand without extra work, then the tracehook_* interface
+ * can change so there is no make-work burden on the core code. The
+ * maintainer of core code changing should notify the maintainers of the
+ * tracing code that they need to work out the change.
+ */
+
+#ifndef _LINUX_TRACEHOOK_H
+#define _LINUX_TRACEHOOK_H 1
+
+#include <linux/sched.h>
+#include <linux/ptrace.h>
+#include <linux/security.h>
+#include <linux/task_work.h>
+struct linux_binprm;
+
+/*
+ * ptrace report for syscall entry and exit looks identical.
+ */
+static inline int ptrace_report_syscall(struct pt_regs *regs)
+{
+ int ptrace = current->ptrace;
+
+ if (!(ptrace & PT_PTRACED))
+ return 0;
+
+ ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));
+
+ /*
+ * this isn't the same as continuing with a signal, but it will do
+ * for normal use. strace only continues with a signal if the
+ * stopping signal is not SIGTRAP. -brl
+ */
+ if (current->exit_code) {
+ send_sig(current->exit_code, current, 1);
+ current->exit_code = 0;
+ }
+
+ return fatal_signal_pending(current);
+}
+
+/**
+ * tracehook_report_syscall_entry - task is about to attempt a system call
+ * @regs: user register state of current task
+ *
+ * This will be called if %TIF_SYSCALL_TRACE has been set, when the
+ * current task has just entered the kernel for a system call.
+ * Full user register state is available here. Changing the values
+ * in @regs can affect the system call number and arguments to be tried.
+ * It is safe to block here, preventing the system call from beginning.
+ *
+ * Returns zero normally, or nonzero if the calling arch code should abort
+ * the system call. That must prevent normal entry so no system call is
+ * made. If @task ever returns to user mode after this, its register state
+ * is unspecified, but should be something harmless like an %ENOSYS error
+ * return. It should preserve enough information so that syscall_rollback()
+ * can work (see asm-generic/syscall.h).
+ *
+ * Called without locks, just after entering kernel mode.
+ */
+static inline __must_check int tracehook_report_syscall_entry(
+ struct pt_regs *regs)
+{
+ return ptrace_report_syscall(regs);
+}
+
+/**
+ * tracehook_report_syscall_exit - task has just finished a system call
+ * @regs: user register state of current task
+ * @step: nonzero if simulating single-step or block-step
+ *
+ * This will be called if %TIF_SYSCALL_TRACE has been set, when the
+ * current task has just finished an attempted system call. Full
+ * user register state is available here. It is safe to block here,
+ * preventing signals from being processed.
+ *
+ * If @step is nonzero, this report is also in lieu of the normal
+ * trap that would follow the system call instruction because
+ * user_enable_block_step() or user_enable_single_step() was used.
+ * In this case, %TIF_SYSCALL_TRACE might not be set.
+ *
+ * Called without locks, just before checking for pending signals.
+ */
+static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
+{
+ if (step) {
+ siginfo_t info;
+ user_single_step_siginfo(current, regs, &info);
+ force_sig_info(SIGTRAP, &info, current);
+ return;
+ }
+
+ ptrace_report_syscall(regs);
+}
+
+/**
+ * tracehook_signal_handler - signal handler setup is complete
+ * @stepping: nonzero if debugger single-step or block-step in use
+ *
+ * Called by the arch code after a signal handler has been set up.
+ * Register and stack state reflects the user handler about to run.
+ * Signal mask changes have already been made.
+ *
+ * Called without locks, shortly before returning to user mode
+ * (or handling more signals).
+ */
+static inline void tracehook_signal_handler(int stepping)
+{
+ if (stepping)
+ ptrace_notify(SIGTRAP);
+}
+
+/**
+ * set_notify_resume - cause tracehook_notify_resume() to be called
+ * @task: task that will call tracehook_notify_resume()
+ *
+ * Calling this arranges that @task will call tracehook_notify_resume()
+ * before returning to user mode. If it's already running in user mode,
+ * it will enter the kernel and call tracehook_notify_resume() soon.
+ * If it's blocked, it will not be woken.
+ */
+static inline void set_notify_resume(struct task_struct *task)
+{
+#ifdef TIF_NOTIFY_RESUME
+ if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_RESUME))
+ kick_process(task);
+#endif
+}
+
+/**
+ * tracehook_notify_resume - report when about to return to user mode
+ * @regs: user-mode registers of @current task
+ *
+ * This is called when %TIF_NOTIFY_RESUME has been set. Now we are
+ * about to return to user mode, and the user state in @regs can be
+ * inspected or adjusted. The caller in arch code has cleared
+ * %TIF_NOTIFY_RESUME before the call. If the flag gets set again
+ * asynchronously, this will be called again before we return to
+ * user mode.
+ *
+ * Called without locks.
+ */
+static inline void tracehook_notify_resume(struct pt_regs *regs)
+{
+ /*
+ * The caller just cleared TIF_NOTIFY_RESUME. This barrier
+ * pairs with task_work_add()->set_notify_resume() after
+ * hlist_add_head(task->task_works);
+ */
+ smp_mb__after_atomic();
+ if (unlikely(current->task_works))
+ task_work_run();
+}
+
+#endif /* <linux/tracehook.h> */
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