四、Windows NT的中断处理
中断是硬件提供的体制，NT系统下大致的中断处理可以参考图4-0。

4.1 中断
正常情况下，处理器会按照指令流按顺序执行指令，但很可能有意外情况需要处理器暂时停止完成原先的任务，去处理各种紧急的情况。一个很简单的情况是：程序需要访问的数据不在物理内存中，就会产生“缺页中断”，处理器会将控制权先交给系统的内存管理器，待完成页交换后，再使原程序继续执行。
4.2 IA32架构的中断处理机制
这节简单地描述IA32架构下硬件的中断处理机制，如果希望能详细了解其中的每一个细节，请参考《IA-32 架构软件开发人员手册》。
当一个中断产生的时候，处理器会根据中断号去查找“中断描述符表”（IDT，有时称为中断向量表）。至于IDT的位置,CPU中有一个专门的寄存器IDTR用于保存IDT的指针。
IDT中每一个描述符为64位，内部记录了中断处理例程的地址和一些描述符。这些描述符中，DPL位用于记载中断的权限，以防止低权限代码访问敏感系统例程，另外I/T标志用来表述这个中断是中断还是陷阱。两者的区别是：中断会把EFLAGE寄存器中的IF位设置为0，从而暂时屏蔽中断（不可屏蔽中断不受影响），直到执行iret指令恢复该标志。同样，IA32处理器也通过中断的方式处理异常。
图4-1和图4-2是IA32手册中关于中断号（包含异常）的一些定义：

  
图4-3是IA32手册中关于中断涉及到三种描述符的定义：

另外，当异常产生时（用int指令直接生成除外）CPU会把异常号入栈。
4.3 NT系统的中断和异常处理机制
Windows NT并不会完全控制中断的处理，只是在IDT表中填入了一些异常处理函数和一部分中断处理函数。以下是Windows NT下IDT的原型：

_IDT            label byte

IDTEntry        _KiTrap00, D_INT032             ; 0: Divide Error
IDTEntry        _KiTrap01, D_INT032             ; 1: DEBUG TRAP
IDTEntry        _KiTrap02, D_INT032             ; 2: NMI/NPX Error
IDTEntry        _KiTrap03, D_INT332             ; 3: Breakpoint
IDTEntry        _KiTrap04, D_INT332             ; 4: INTO
IDTEntry        _KiTrap05, D_INT032             ; 5: BOUND/Print Screen
IDTEntry        _KiTrap06, D_INT032             ; 6: Invalid Opcode
IDTEntry        _KiTrap07, D_INT032             ; 7: NPX Not Available
IDTEntry        _KiTrap08, D_INT032             ; 8: Double Exception
IDTEntry        _KiTrap09, D_INT032             ; 9: NPX Segment Overrun
IDTEntry        _KiTrap0A, D_INT032             ; A: Invalid TSS
IDTEntry        _KiTrap0B, D_INT032             ; B: Segment Not Present
IDTEntry        _KiTrap0C, D_INT032             ; C: Stack Fault
IDTEntry        _KiTrap0D, D_INT032             ; D: General Protection
IDTEntry        _KiTrap0E, D_INT032             ; E: Page Fault
IDTEntry        _KiTrap0F, D_INT032             ; F: Intel Reserved

IDTEntry        _KiTrap10, D_INT032             ;10: 486 coprocessor error
IDTEntry        _KiTrap11, D_INT032             ;11: 486 alignment
IDTEntry        _KiTrap0F, D_INT032             ;12: Intel Reserved
IDTEntry        _KiTrap0F, D_INT032             ;13: XMMI unmasked numeric exception
IDTEntry        _KiTrap0F, D_INT032             ;14: Intel Reserved
IDTEntry        _KiTrap0F, D_INT032             ;15: Intel Reserved
IDTEntry        _KiTrap0F, D_INT032             ;16: Intel Reserved
IDTEntry        _KiTrap0F, D_INT032             ;17: Intel Reserved

IDTEntry        _KiTrap0F, D_INT032             ;18: Intel Reserved
IDTEntry        _KiTrap0F, D_INT032             ;19: Intel Reserved
IDTEntry        _KiTrap0F, D_INT032             ;1A: Intel Reserved
IDTEntry        _KiTrap0F, D_INT032             ;1B: Intel Reserved
IDTEntry        _KiTrap0F, D_INT032             ;1C: Intel Reserved
IDTEntry        _KiTrap0F, D_INT032             ;1D: Intel Reserved
IDTEntry        _KiTrap0F, D_INT032             ;1E: Intel Reserved
IDTEntry        _KiTrap0F, D_INT032             ;1F: Reserved for APIC

;
; Note IDTEntry 0x21 is reserved for WOW apps.
;

        rept 2AH - (($ - _IDT)/8)
IDTEntry        0, 0                            invalid IDT entry
        endm
IDTEntry        _KiGetTickCount,  D_INT332          2A: KiGetTickCount service
IDTEntry        _KiCallbackReturn,  D_INT332        2B: KiCallbackReturn
IDTEntry        _KiRaiseAssertion,  D_INT332        2C: KiRaiseAssertion service
IDTEntry        _KiDebugService,  D_INT332          2D: debugger calls
IDTEntry        _KiSystemService, D_INT332          2E: system service calls
IDTEntry        _KiTrap0F, D_INT032                 ;2F: Reserved for APIC

以下是Windows NT5.1.2600（XP SP3）登录后通过调试得到的IDT信息。

00:    80543250 nt!KiTrap00
01:    805433cc nt!KiTrap01
02:    Task Selector = 0x0058
03:    805437e0 nt!KiTrap03
04:    80543960 nt!KiTrap04
05:    80543ac0 nt!KiTrap05
06:    80543c34 nt!KiTrap06
07:    805442ac nt!KiTrap07
08:    Task Selector = 0x0050
09:    805446b0 nt!KiTrap09
0a:    805447d0 nt!KiTrap0A
0b:    80544910 nt!KiTrap0B
0c:    80544b70 nt!KiTrap0C
0d:    80544e5c nt!KiTrap0D
0e:    80545570 nt!KiTrap0E
0f:    805458a8 nt!KiTrap0F
10:    805459c8 nt!KiTrap10
11:    80545b04 nt!KiTrap11
12:    Task Selector = 0x00A0
13:    80545c6c nt!KiTrap13
14:    805458a8 nt!KiTrap0F
15:    805458a8 nt!KiTrap0F
16:    805458a8 nt!KiTrap0F
17:    805458a8 nt!KiTrap0F
18:    805458a8 nt!KiTrap0F
19:    805458a8 nt!KiTrap0F
1a:    805458a8 nt!KiTrap0F
1b:    805458a8 nt!KiTrap0F
1c:    805458a8 nt!KiTrap0F
1d:    805458a8 nt!KiTrap0F
1e:    805458a8 nt!KiTrap0F
1f:    806e810c hal!HalpApicSpuriousService
20:    00000000
21:    00000000
22:    00000000
23:    00000000
24:    00000000
25:    00000000
26:    00000000
27:    00000000
28:    00000000
29:    00000000
2a:    80542a7e nt!KiGetTickCount
2b:    80542b80 nt!KiCallbackReturn
2c:    80542d30 nt!KiSetLowWaitHighThread
2d:    805436bc nt!KiDebugService
2e:    80542501 nt!KiSystemService
2f:    805458a8 nt!KiTrap0F
30:    80541bc0 nt!KiUnexpectedInterrupt0
31:    80541bca nt!KiUnexpectedInterrupt1
32:    80541bd4 nt!KiUnexpectedInterrupt2
33:    80541bde nt!KiUnexpectedInterrupt3
34:    80541be8 nt!KiUnexpectedInterrupt4
35:    80541bf2 nt!KiUnexpectedInterrupt5
36:    80541bfc nt!KiUnexpectedInterrupt6
37:    806e7864 hal!PicSpuriousService37
38:    80541c10 nt!KiUnexpectedInterrupt8
39:    80541c1a nt!KiUnexpectedInterrupt9
3a:    80541c24 nt!KiUnexpectedInterrupt10
3b:    80541c2e nt!KiUnexpectedInterrupt11
3c:    80541c38 nt!KiUnexpectedInterrupt12
3d:    806e8e2c hal!HalpApcInterrupt
3e:    80541c4c nt!KiUnexpectedInterrupt14
3f:    80541c56 nt!KiUnexpectedInterrupt15
40:    80541c60 nt!KiUnexpectedInterrupt16
41:    806e8c88 hal!HalpDispatchInterrupt
42:    80541c74 nt!KiUnexpectedInterrupt18
43:    80541c7e nt!KiUnexpectedInterrupt19
44:    80541c88 nt!KiUnexpectedInterrupt20
45:    80541c92 nt!KiUnexpectedInterrupt21
46:    80541c9c nt!KiUnexpectedInterrupt22
47:    80541ca6 nt!KiUnexpectedInterrupt23
48:    80541cb0 nt!KiUnexpectedInterrupt24
49:    80541cba nt!KiUnexpectedInterrupt25
4a:    80541cc4 nt!KiUnexpectedInterrupt26
4b:    80541cce nt!KiUnexpectedInterrupt27
4c:    80541cd8 nt!KiUnexpectedInterrupt28
4d:    80541ce2 nt!KiUnexpectedInterrupt29
4e:    80541cec nt!KiUnexpectedInterrupt30
4f:    80541cf6 nt!KiUnexpectedInterrupt31
50:    806e793c hal!HalpApicRebootService
51:    80541d0a nt!KiUnexpectedInterrupt33
52:    80541d14 nt!KiUnexpectedInterrupt34
53:    80541d1e nt!KiUnexpectedInterrupt35
54:    80541d28 nt!KiUnexpectedInterrupt36
55:    80541d32 nt!KiUnexpectedInterrupt37
56:    80541d3c nt!KiUnexpectedInterrupt38
57:    80541d46 nt!KiUnexpectedInterrupt39
58:    80541d50 nt!KiUnexpectedInterrupt40
59:    80541d5a nt!KiUnexpectedInterrupt41
5a:    80541d64 nt!KiUnexpectedInterrupt42
5b:    80541d6e nt!KiUnexpectedInterrupt43
5c:    80541d78 nt!KiUnexpectedInterrupt44
5d:    80541d82 nt!KiUnexpectedInterrupt45
5e:    80541d8c nt!KiUnexpectedInterrupt46
5f:    80541d96 nt!KiUnexpectedInterrupt47
60:    80541da0 nt!KiUnexpectedInterrupt48
61:    80541daa nt!KiUnexpectedInterrupt49
62:    89c93044 atapi!IdePortInterrupt (KINTERRUPT 89c93008)
63:    89a0d4f4 USBPORT!USBPORT_InterruptService (KINTERRUPT 89a0d4b8)
64:    80541dc8 nt!KiUnexpectedInterrupt52
65:    80541dd2 nt!KiUnexpectedInterrupt53
66:    80541ddc nt!KiUnexpectedInterrupt54
67:    80541de6 nt!KiUnexpectedInterrupt55
68:    80541df0 nt!KiUnexpectedInterrupt56
69:    80541dfa nt!KiUnexpectedInterrupt57
6a:    80541e04 nt!KiUnexpectedInterrupt58
6b:    80541e0e nt!KiUnexpectedInterrupt59
6c:    80541e18 nt!KiUnexpectedInterrupt60
6d:    80541e22 nt!KiUnexpectedInterrupt61
6e:    80541e2c nt!KiUnexpectedInterrupt62
6f:    80541e36 nt!KiUnexpectedInterrupt63
70:    80541e40 nt!KiUnexpectedInterrupt64
71:    80541e4a nt!KiUnexpectedInterrupt65
72:    80541e54 nt!KiUnexpectedInterrupt66
73:    89905044 SCSIPORT!ScsiPortInterrupt (KINTERRUPT 89905008)
             USBPORT!USBPORT_InterruptService (KINTERRUPT 89d02008)
74:    80541e68 nt!KiUnexpectedInterrupt68
75:    80541e72 nt!KiUnexpectedInterrupt69
76:    80541e7c nt!KiUnexpectedInterrupt70
77:    80541e86 nt!KiUnexpectedInterrupt71
78:    80541e90 nt!KiUnexpectedInterrupt72
79:    80541e9a nt!KiUnexpectedInterrupt73
7a:    80541ea4 nt!KiUnexpectedInterrupt74
7b:    80541eae nt!KiUnexpectedInterrupt75
7c:    80541eb8 nt!KiUnexpectedInterrupt76
7d:    80541ec2 nt!KiUnexpectedInterrupt77
7e:    80541ecc nt!KiUnexpectedInterrupt78
7f:    80541ed6 nt!KiUnexpectedInterrupt79
80:    80541ee0 nt!KiUnexpectedInterrupt80
81:    80541eea nt!KiUnexpectedInterrupt81
82:    89cfe044 atapi!IdePortInterrupt (KINTERRUPT 89cfe008)
83:    89d5a044 *** ERROR: Symbol file could not be found.  Defaulted to export symbols for XXXXXXXs -
vmci!DllUnload+0x7D6 (KINTERRUPT 89d5a008)
             VIDEOPRT!pVideoPortInterrupt (KINTERRUPT 89d01310)
             portcls!CKsShellRequestor::`scalar deleting destructor'+0x26 (KINTERRUPT 89d7c7e8)
84:    80541f08 nt!KiUnexpectedInterrupt84
85:    80541f12 nt!KiUnexpectedInterrupt85
86:    80541f1c nt!KiUnexpectedInterrupt86
87:    80541f26 nt!KiUnexpectedInterrupt87
88:    80541f30 nt!KiUnexpectedInterrupt88
89:    80541f3a nt!KiUnexpectedInterrupt89
8a:    80541f44 nt!KiUnexpectedInterrupt90
8b:    80541f4e nt!KiUnexpectedInterrupt91
8c:    80541f58 nt!KiUnexpectedInterrupt92
8d:    80541f62 nt!KiUnexpectedInterrupt93
8e:    80541f6c nt!KiUnexpectedInterrupt94
8f:    80541f76 nt!KiUnexpectedInterrupt95
90:    80541f80 nt!KiUnexpectedInterrupt96
91:    80541f8a nt!KiUnexpectedInterrupt97
92:    897c7824 serial!SerialCIsrSw (KINTERRUPT 897c77e8)
93:    89c96044 i8042prt!I8042KeyboardInterruptService (KINTERRUPT 89c96008)
94:    80541fa8 nt!KiUnexpectedInterrupt100
95:    80541fb2 nt!KiUnexpectedInterrupt101
96:    80541fbc nt!KiUnexpectedInterrupt102
97:    80541fc6 nt!KiUnexpectedInterrupt103
98:    80541fd0 nt!KiUnexpectedInterrupt104
99:    80541fda nt!KiUnexpectedInterrupt105
9a:    80541fe4 nt!KiUnexpectedInterrupt106
9b:    80541fee nt!KiUnexpectedInterrupt107
9c:    80541ff8 nt!KiUnexpectedInterrupt108
9d:    80542002 nt!KiUnexpectedInterrupt109
9e:    8054200c nt!KiUnexpectedInterrupt110
9f:    80542016 nt!KiUnexpectedInterrupt111
a0:    80542020 nt!KiUnexpectedInterrupt112
a1:    8054202a nt!KiUnexpectedInterrupt113
a2:    80542034 nt!KiUnexpectedInterrupt114
a3:    89c95044 i8042prt!I8042MouseInterruptService (KINTERRUPT 89c95008)
a4:    80542048 nt!KiUnexpectedInterrupt116
a5:    80542052 nt!KiUnexpectedInterrupt117
a6:    8054205c nt!KiUnexpectedInterrupt118
a7:    80542066 nt!KiUnexpectedInterrupt119
a8:    80542070 nt!KiUnexpectedInterrupt120
a9:    8054207a nt!KiUnexpectedInterrupt121
aa:    80542084 nt!KiUnexpectedInterrupt122
ab:    8054208e nt!KiUnexpectedInterrupt123
ac:    80542098 nt!KiUnexpectedInterrupt124
ad:    805420a2 nt!KiUnexpectedInterrupt125
ae:    805420ac nt!KiUnexpectedInterrupt126
af:    805420b6 nt!KiUnexpectedInterrupt127
b0:    805420c0 nt!KiUnexpectedInterrupt128
b1:    89dac044 ACPI!ACPIInterruptServiceRoutine (KINTERRUPT 89dac008)
b2:    89c4f824 serial!SerialCIsrSw (KINTERRUPT 89c4f7e8)
b3:    805420de nt!KiUnexpectedInterrupt131
b4:    898fd044 NDIS!ndisMIsr (KINTERRUPT 898fd008)
b5:    805420f2 nt!KiUnexpectedInterrupt133
b6:    805420fc nt!KiUnexpectedInterrupt134
b7:    80542106 nt!KiUnexpectedInterrupt135
b8:    80542110 nt!KiUnexpectedInterrupt136
b9:    8054211a nt!KiUnexpectedInterrupt137
ba:    80542124 nt!KiUnexpectedInterrupt138
bb:    8054212e nt!KiUnexpectedInterrupt139
bc:    80542138 nt!KiUnexpectedInterrupt140
bd:    80542142 nt!KiUnexpectedInterrupt141
be:    8054214c nt!KiUnexpectedInterrupt142
bf:    80542156 nt!KiUnexpectedInterrupt143
c0:    80542160 nt!KiUnexpectedInterrupt144
c1:    806e7ac0 hal!HalpBroadcastCallService
c2:    80542174 nt!KiUnexpectedInterrupt146
c3:    8054217e nt!KiUnexpectedInterrupt147
c4:    80542188 nt!KiUnexpectedInterrupt148
c5:    80542192 nt!KiUnexpectedInterrupt149
c6:    8054219c nt!KiUnexpectedInterrupt150
c7:    805421a6 nt!KiUnexpectedInterrupt151
c8:    805421b0 nt!KiUnexpectedInterrupt152
c9:    805421ba nt!KiUnexpectedInterrupt153
ca:    805421c4 nt!KiUnexpectedInterrupt154
cb:    805421ce nt!KiUnexpectedInterrupt155
cc:    805421d8 nt!KiUnexpectedInterrupt156
cd:    805421e2 nt!KiUnexpectedInterrupt157
ce:    805421ec nt!KiUnexpectedInterrupt158
cf:    805421f6 nt!KiUnexpectedInterrupt159
d0:    80542200 nt!KiUnexpectedInterrupt160
d1:    806e6e54 hal!HalpClockInterrupt
d2:    80542214 nt!KiUnexpectedInterrupt162
d3:    8054221e nt!KiUnexpectedInterrupt163
d4:    80542228 nt!KiUnexpectedInterrupt164
d5:    80542232 nt!KiUnexpectedInterrupt165
d6:    8054223c nt!KiUnexpectedInterrupt166
d7:    80542246 nt!KiUnexpectedInterrupt167
d8:    80542250 nt!KiUnexpectedInterrupt168
d9:    8054225a nt!KiUnexpectedInterrupt169
da:    80542264 nt!KiUnexpectedInterrupt170
db:    8054226e nt!KiUnexpectedInterrupt171
dc:    80542278 nt!KiUnexpectedInterrupt172
dd:    80542282 nt!KiUnexpectedInterrupt173
de:    8054228c nt!KiUnexpectedInterrupt174
df:    80542296 nt!KiUnexpectedInterrupt175
e0:    805422a0 nt!KiUnexpectedInterrupt176
e1:    806e8048 hal!HalpIpiHandler
e2:    805422b4 nt!KiUnexpectedInterrupt178
e3:    806e7dac hal!HalpLocalApicErrorService
e4:    805422c8 nt!KiUnexpectedInterrupt180
e5:    805422d2 nt!KiUnexpectedInterrupt181
e6:    805422dc nt!KiUnexpectedInterrupt182
e7:    805422e6 nt!KiUnexpectedInterrupt183
e8:    805422f0 nt!KiUnexpectedInterrupt184
e9:    805422fa nt!KiUnexpectedInterrupt185
ea:    80542304 nt!KiUnexpectedInterrupt186
eb:    8054230e nt!KiUnexpectedInterrupt187
ec:    80542318 nt!KiUnexpectedInterrupt188
ed:    80542322 nt!KiUnexpectedInterrupt189
ee:    80542329 nt!KiUnexpectedInterrupt190
ef:    80542330 nt!KiUnexpectedInterrupt191
f0:    80542337 nt!KiUnexpectedInterrupt192
f1:    8054233e nt!KiUnexpectedInterrupt193
f2:    80542345 nt!KiUnexpectedInterrupt194
f3:    8054234c nt!KiUnexpectedInterrupt195
f4:    80542353 nt!KiUnexpectedInterrupt196
f5:    8054235a nt!KiUnexpectedInterrupt197
f6:    80542361 nt!KiUnexpectedInterrupt198
f7:    80542368 nt!KiUnexpectedInterrupt199
f8:    8054236f nt!KiUnexpectedInterrupt200
f9:    80542376 nt!KiUnexpectedInterrupt201
fa:    8054237d nt!KiUnexpectedInterrupt202
fb:    80542384 nt!KiUnexpectedInterrupt203
fc:    8054238b nt!KiUnexpectedInterrupt204
fd:    806e85a8 hal!HalpProfileInterrupt
fe:    806e8748 hal!HalpPerfInterrupt
ff:    805423a0 nt!KiUnexpectedInterrupt207

可以看到，IDT中相当多的项目并未被使用（处理例程被指定为KiUnexpectedInterruptXX），内核程序可以自行操作IDT添加一个属于自己中断。
另外，NT系统还提供了中断对象机制来供内核程序使用，可以在不直接操作IDT的情况下添加自己的中断处理例程，这里不作介绍。
4.4Windows的中断优先级
IA32架构中的APIC（高级可编程中断控制器）提供了对中断优先级的支持，Windows NT在此基础上自定义了自己中断优先方案，称为中断请求级别（IRQL），优先级从0-31，数值越大优先级越高。

#define PASSIVE_LEVEL 0             // Passive release level
#define LOW_LEVEL 0                 // Lowest interrupt level
#define APC_LEVEL 1                 // APC interrupt level
#define DISPATCH_LEVEL 2            // Dispatcher level
#define PROFILE_LEVEL 27            // timer used for profiling.
#define CLOCK1_LEVEL 28             // Interval clock 1 level - Not used on x86
#define CLOCK2_LEVEL 28             // Interval clock 2 level
#define IPI_LEVEL 29                // Interprocessor interrupt level
#define POWER_LEVEL 30              // Power failure level
#define HIGH_LEVEL 31               // Highest interrupt level

PASSIVE_LEVEL 为最低的优先级别，用户进程的IRQL=PASSIVE_LEVEL ，所以可以被任何拥有更高级别的中断打断。
APC（异步过程调用）的优先级APC_LEVEL比PASSIVE_LEVEL 稍高，在此之上则是DISPATCH_LEVEL ，线程调度器和DPC（延时过程调用）的IRQL=DISPATCH_LEVEL 。
关于APC和DPC，本文不作介绍。
3-26的IRQL分配给硬件中断，在此之上则为关键的时钟中断和一些性能计数器设计的中断使用。硬件中断的优先问题还涉及到APIC本身，在这不作介绍。