请教arch/x86/kernel/traps.c中的do_debug函数是做什么的

cuic139

请教谁知道arch/x86/kernel/traps.c中的do_debug函数是做什么的，调用流程和调用原因是怎样的？，谢谢

1. 
   
2. /*
   
3. * Our handling of the processor debug registers is non-trivial.
   
4. * We do not clear them on entry and exit from the kernel. Therefore
   
5. * it is possible to get a watchpoint trap here from inside the kernel.
   
6. * However, the code in ./ptrace.c has ensured that the user can
   
7. * only set watchpoints on userspace addresses. Therefore the in-kernel
   
8. * watchpoint trap can only occur in code which is reading/writing
   
9. * from user space. Such code must not hold kernel locks (since it
   
10. * can equally take a page fault), therefore it is safe to call
    
11. * force_sig_info even though that claims and releases locks.
    
12. *
    
13. * Code in ./signal.c ensures that the debug control register
    
14. * is restored before we deliver any signal, and therefore that
    
15. * user code runs with the correct debug control register even though
    
16. * we clear it here.
    
17. *
    
18. * Being careful here means that we don't have to be as careful in a
    
19. * lot of more complicated places (task switching can be a bit lazy
    
20. * about restoring all the debug state, and ptrace doesn't have to
    
21. * find every occurrence of the TF bit that could be saved away even
    
22. * by user code)
    
23. *
    
24. * May run on IST stack.
    
25. */
    
26. dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
    
27. {
    
28.         struct task_struct *tsk = current;
    
29.         int user_icebp = 0;
    
30.         unsigned long dr6;
    
31.         int si_code;
    
32. 
    
33.         get_debugreg(dr6, 6);
    
34. 
    
35.         /* Filter out all the reserved bits which are preset to 1 */
    
36.         dr6 &= ~DR6_RESERVED;
    
37. 
    
38.         /*
    
39.          * If dr6 has no reason to give us about the origin of this trap,
    
40.          * then it's very likely the result of an icebp/int01 trap.
    
41.          * User wants a sigtrap for that.
    
42.          */
    
43.         if (!dr6 && user_mode(regs))
    
44.                 user_icebp = 1;
    
45. 
    
46.         /* Catch kmemcheck conditions first of all! */
    
47.         if ((dr6 & DR_STEP) && kmemcheck_trap(regs))
    
48.                 return;
    
49. 
    
50.         /* DR6 may or may not be cleared by the CPU */
    
51.         set_debugreg(0, 6);
    
52. 
    
53.         /*
    
54.          * The processor cleared BTF, so don't mark that we need it set.
    
55.          */
    
56.         clear_tsk_thread_flag(tsk, TIF_BLOCKSTEP);
    
57. 
    
58.         /* Store the virtualized DR6 value */
    
59.         tsk->thread.debugreg6 = dr6;
    
60. 
    
61. #ifdef  CONFIG_KDB
    
62.         if (kdb(LKDB_REASON_DEBUG, error_code, regs))
    
63.         {
    
64.                 return;
    
65.         }
    
66. #endif  /* CONFIG_KDB */
    
67. 
    
68.         if (notify_die(DIE_DEBUG, "debug", regs, PTR_ERR(&dr6), error_code,
    
69.                                                         SIGTRAP) == NOTIFY_STOP)
    
70.                 return;
    
71. 
    
72.         /* It's safe to allow irq's after DR6 has been saved */
    
73.         preempt_conditional_sti(regs);
    
74. 
    
75.         if (regs->flags & X86_VM_MASK) {
    
76.                 handle_vm86_trap((struct kernel_vm86_regs *) regs,
    
77.                                 error_code, 1);
    
78.                 preempt_conditional_cli(regs);
    
79.                 return;
    
80.         }
    
81. 
    
82.         /*
    
83.          * Single-stepping through system calls: ignore any exceptions in
    
84.          * kernel space, but re-enable TF when returning to user mode.
    
85.          *
    
86.          * We already checked v86 mode above, so we can check for kernel mode
    
87.          * by just checking the CPL of CS.
    
88.          */
    
89.         if ((dr6 & DR_STEP) && !user_mode(regs)) {
    
90.                 tsk->thread.debugreg6 &= ~DR_STEP;
    
91.                 set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
    
92.                 regs->flags &= ~X86_EFLAGS_TF;
    
93.         }
    
94.         si_code = get_si_code(tsk->thread.debugreg6);
    
95.         if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp)
    
96.                 send_sigtrap(tsk, regs, error_code, si_code);
    
97.         preempt_conditional_cli(regs);
    
98. 
    
99.         return;
    
100. }
     

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