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* 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.
#include <linux/sched.h>
#include <linux/ptrace.h>
#include <linux/security.h>
#include <linux/task_work.h>
#include <linux/memcontrol.h>
#include <linux/blk-cgroup.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);
* 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)
* 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)
if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_RESUME))
* 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);
if (unlikely(current->task_works))
#endif /* <linux/tracehook.h> */