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Linux/include/linux/tracehook.h

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  1 /*
  2  * Tracing hooks
  3  *
  4  * Copyright (C) 2008-2009 Red Hat, Inc.  All rights reserved.
  5  *
  6  * This copyrighted material is made available to anyone wishing to use,
  7  * modify, copy, or redistribute it subject to the terms and conditions
  8  * of the GNU General Public License v.2.
  9  *
 10  * This file defines hook entry points called by core code where
 11  * user tracing/debugging support might need to do something.  These
 12  * entry points are called tracehook_*().  Each hook declared below
 13  * has a detailed kerneldoc comment giving the context (locking et
 14  * al) from which it is called, and the meaning of its return value.
 15  *
 16  * Each function here typically has only one call site, so it is ok
 17  * to have some nontrivial tracehook_*() inlines.  In all cases, the
 18  * fast path when no tracing is enabled should be very short.
 19  *
 20  * The purpose of this file and the tracehook_* layer is to consolidate
 21  * the interface that the kernel core and arch code uses to enable any
 22  * user debugging or tracing facility (such as ptrace).  The interfaces
 23  * here are carefully documented so that maintainers of core and arch
 24  * code do not need to think about the implementation details of the
 25  * tracing facilities.  Likewise, maintainers of the tracing code do not
 26  * need to understand all the calling core or arch code in detail, just
 27  * documented circumstances of each call, such as locking conditions.
 28  *
 29  * If the calling core code changes so that locking is different, then
 30  * it is ok to change the interface documented here.  The maintainer of
 31  * core code changing should notify the maintainers of the tracing code
 32  * that they need to work out the change.
 33  *
 34  * Some tracehook_*() inlines take arguments that the current tracing
 35  * implementations might not necessarily use.  These function signatures
 36  * are chosen to pass in all the information that is on hand in the
 37  * caller and might conceivably be relevant to a tracer, so that the
 38  * core code won't have to be updated when tracing adds more features.
 39  * If a call site changes so that some of those parameters are no longer
 40  * already on hand without extra work, then the tracehook_* interface
 41  * can change so there is no make-work burden on the core code.  The
 42  * maintainer of core code changing should notify the maintainers of the
 43  * tracing code that they need to work out the change.
 44  */
 45 
 46 #ifndef _LINUX_TRACEHOOK_H
 47 #define _LINUX_TRACEHOOK_H      1
 48 
 49 #include <linux/sched.h>
 50 #include <linux/ptrace.h>
 51 #include <linux/security.h>
 52 #include <linux/task_work.h>
 53 #include <linux/memcontrol.h>
 54 struct linux_binprm;
 55 
 56 /*
 57  * ptrace report for syscall entry and exit looks identical.
 58  */
 59 static inline int ptrace_report_syscall(struct pt_regs *regs)
 60 {
 61         int ptrace = current->ptrace;
 62 
 63         if (!(ptrace & PT_PTRACED))
 64                 return 0;
 65 
 66         ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));
 67 
 68         /*
 69          * this isn't the same as continuing with a signal, but it will do
 70          * for normal use.  strace only continues with a signal if the
 71          * stopping signal is not SIGTRAP.  -brl
 72          */
 73         if (current->exit_code) {
 74                 send_sig(current->exit_code, current, 1);
 75                 current->exit_code = 0;
 76         }
 77 
 78         return fatal_signal_pending(current);
 79 }
 80 
 81 /**
 82  * tracehook_report_syscall_entry - task is about to attempt a system call
 83  * @regs:               user register state of current task
 84  *
 85  * This will be called if %TIF_SYSCALL_TRACE has been set, when the
 86  * current task has just entered the kernel for a system call.
 87  * Full user register state is available here.  Changing the values
 88  * in @regs can affect the system call number and arguments to be tried.
 89  * It is safe to block here, preventing the system call from beginning.
 90  *
 91  * Returns zero normally, or nonzero if the calling arch code should abort
 92  * the system call.  That must prevent normal entry so no system call is
 93  * made.  If @task ever returns to user mode after this, its register state
 94  * is unspecified, but should be something harmless like an %ENOSYS error
 95  * return.  It should preserve enough information so that syscall_rollback()
 96  * can work (see asm-generic/syscall.h).
 97  *
 98  * Called without locks, just after entering kernel mode.
 99  */
100 static inline __must_check int tracehook_report_syscall_entry(
101         struct pt_regs *regs)
102 {
103         return ptrace_report_syscall(regs);
104 }
105 
106 /**
107  * tracehook_report_syscall_exit - task has just finished a system call
108  * @regs:               user register state of current task
109  * @step:               nonzero if simulating single-step or block-step
110  *
111  * This will be called if %TIF_SYSCALL_TRACE has been set, when the
112  * current task has just finished an attempted system call.  Full
113  * user register state is available here.  It is safe to block here,
114  * preventing signals from being processed.
115  *
116  * If @step is nonzero, this report is also in lieu of the normal
117  * trap that would follow the system call instruction because
118  * user_enable_block_step() or user_enable_single_step() was used.
119  * In this case, %TIF_SYSCALL_TRACE might not be set.
120  *
121  * Called without locks, just before checking for pending signals.
122  */
123 static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
124 {
125         if (step) {
126                 siginfo_t info;
127                 user_single_step_siginfo(current, regs, &info);
128                 force_sig_info(SIGTRAP, &info, current);
129                 return;
130         }
131 
132         ptrace_report_syscall(regs);
133 }
134 
135 /**
136  * tracehook_signal_handler - signal handler setup is complete
137  * @stepping:           nonzero if debugger single-step or block-step in use
138  *
139  * Called by the arch code after a signal handler has been set up.
140  * Register and stack state reflects the user handler about to run.
141  * Signal mask changes have already been made.
142  *
143  * Called without locks, shortly before returning to user mode
144  * (or handling more signals).
145  */
146 static inline void tracehook_signal_handler(int stepping)
147 {
148         if (stepping)
149                 ptrace_notify(SIGTRAP);
150 }
151 
152 /**
153  * set_notify_resume - cause tracehook_notify_resume() to be called
154  * @task:               task that will call tracehook_notify_resume()
155  *
156  * Calling this arranges that @task will call tracehook_notify_resume()
157  * before returning to user mode.  If it's already running in user mode,
158  * it will enter the kernel and call tracehook_notify_resume() soon.
159  * If it's blocked, it will not be woken.
160  */
161 static inline void set_notify_resume(struct task_struct *task)
162 {
163 #ifdef TIF_NOTIFY_RESUME
164         if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_RESUME))
165                 kick_process(task);
166 #endif
167 }
168 
169 /**
170  * tracehook_notify_resume - report when about to return to user mode
171  * @regs:               user-mode registers of @current task
172  *
173  * This is called when %TIF_NOTIFY_RESUME has been set.  Now we are
174  * about to return to user mode, and the user state in @regs can be
175  * inspected or adjusted.  The caller in arch code has cleared
176  * %TIF_NOTIFY_RESUME before the call.  If the flag gets set again
177  * asynchronously, this will be called again before we return to
178  * user mode.
179  *
180  * Called without locks.
181  */
182 static inline void tracehook_notify_resume(struct pt_regs *regs)
183 {
184         /*
185          * The caller just cleared TIF_NOTIFY_RESUME. This barrier
186          * pairs with task_work_add()->set_notify_resume() after
187          * hlist_add_head(task->task_works);
188          */
189         smp_mb__after_atomic();
190         if (unlikely(current->task_works))
191                 task_work_run();
192 
193         mem_cgroup_handle_over_high();
194 }
195 
196 #endif  /* <linux/tracehook.h> */
197 

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