ARM Linux 中断向量表建立流程

Linux Version : 2.6.29

1. start_kernel-->setup_arch-->early_trap_init

   1:  
    memcpy((void
 *)vectors, __vectors_start, __vectors_end - __vectors_start);

   2:  
    memcpy((void
 *)vectors + 0x200, __stubs_start, __stubs_end - __stubs_start);

   3:  
    memcpy((void
 *)vectors + 0x1000 - kuser_sz, __kuser_helper_start, kuser_sz);

对于第一行：

         __vectors_start 和 __vectors_end 定义在 arch/arm/kernel/entry-armv.S  , 它们之间保存了中断向量表。      

   1:  
    .globl    __vectors_start

   2:  
__vectors_start:

   3:  
    swi    SYS_ERROR0   

   4:  
    b    vector_und + stubs_offset

   5:  
    ldr    pc, .LCvswi + stubs_offset

   6:  
    b    vector_pabt + stubs_offset

   7:  
    b    vector_dabt + stubs_offset

   8:  
    b    vector_addrexcptn + stubs_offset

   9:  
    b    vector_irq + stubs_offset

  10:  
    b    vector_fiq + stubs_offset

  11:  
 

  12:  
    .globl    __vectors_end

  13:  
__vectors_end:

         vectors 的地址为CONFIG_VECTORS_BASE ， 在.config中定义为0xffff0000

         所以 第1行就是把中断向量表拷贝到0xffff0000

  对于第二行： 

             vector_stub是一个带参数的宏，第一个是name，第二个是arm excepiton mode，第三个是为了得到返回地址，lr需要减去的偏移

   1:  
    .macro    vector_stub, name, mode, correction=0

   2:  
    .align    5

   3:  
 

   4:  
vector_/name:

   5:  
    .if
 /correction

   6:  
    sub    lr, lr, #/correction          @得到正确的返回地址

   7:  
    .endif

   8:  
 

   9:  
    @

  10:  
    @ Save r0, lr_ (parent PC) and spsr_

  11:  
    @ (parent CPSR)

  12:  
    @

  13:  
    stmia    sp, {r0, lr}        @ save r0, lr

  14:  
    mrs    lr, spsr

  15:  
    str    lr, [sp, #8]        @ save spsr

  16:  
 

  17:  
    @

  18:  
    @ Prepare for
 SVC32 mode.  IRQs remain disabled.

  19:  
    @ 

  20:  
    mrs    r0, cpsr

  21:  
    eor    r0, r0, #(/mode ^ SVC_MODE) @把cpsr内容与(mode^SVC_mode)异或，即r0里为SVC_MODE      

  22:  
    msr    spsr_cxsf, r0  @把r0的值写入整个spsr寄存器(cxsf表示要往哪个字节写入)

  23:  
 

  24:  
    @

  25:  
    @ the branch table must immediately follow this
 code

  26:  
    @

  27:  
    and    lr, lr, #0x0f  @lr为spsr_的值，此语句取到进入异常前的mode

  28:  
    mov    r0, sp         @ 

  29:  
    ldr    lr, [pc, lr, lsl #2] @lr=pc+mode*4,其中pc为紧接着30的指令,即vector_stub后的第一条指令

  30:  
    movs    pc, lr            @ movs会把spsr的值赋给cpsr，所以branch to handler in
 SVC mode

  31:  
ENDPROC(vector_/name)

  32:  
    .endm

            再来看下vector 跳转表

   1:  
    .long
    __irq_usr            @  0  (USR_26 / USR_32)

   2:  
    .long
    __irq_invalid            @  1  (FIQ_26 / FIQ_32)

   3:  
    .long
    __irq_invalid            @  2  (IRQ_26 / IRQ_32)

   4:  
    .long
    __irq_svc            @  3  (SVC_26 / SVC_32)

   5:  
    .long
    __irq_invalid            @  4

   6:  
    .long
    __irq_invalid            @  5

   7:  
    .long
    __irq_invalid            @  6

   8:  
    .long
    __irq_invalid            @  7

   9:  
    .long
    __irq_invalid            @  8

  10:  
    .long
    __irq_invalid            @  9

  11:  
    .long
    __irq_invalid            @  a

  12:  
    .long
    __irq_invalid            @  b

  13:  
    .long
    __irq_invalid            @  c

  14:  
    .long
    __irq_invalid            @  d

  15:  
    .long
    __irq_invalid            @  e

  16:  
    .long
    __irq_invalid            @  f

             这里只有usr 和svc 有入口，而其他都是invalid ，是因为linux只会从usr(application) 和svc(kernel)两种mode跳转到exception来

          __stubs_start 和 __stubs_end 之间的代码简化后为：

   1:  
__stubs_start:

   2:  
   vector_irq:    @vector_stub    irq, IRQ_MODE, 4

   3:  
   vector_dabt:   @vector_stub    dabt, ABT_MODE, 8

   4:  
   vector_pabt:   @vector_stub    pabt, ABT_MODE, 4

   5:  
   vector_und:    @vector_stub    und, UND_MODE

   6:  
   vector_fiq:

   7:  
   vector_addrexcptn:

   8:  
   .LCvswi:

   9:  
__stubs_end:

          由此可以知道 __stubs_start 和 __stubs_end 之间定义了各种异常的入口

         我们再来看为什么异常入口是“b vector_und + stubs_offset”， 同时为什么stubs_offset 的定义如下

.equ    stubs_offset, __vectors_start + 0x200 - __stubs_start

          arm 的跳转指令b 是跳转到相对于PC的一个偏移地址( offset )，汇编器在编译时会对label 减去PC 得到offset，同时vector 拷贝后是如下排列的

	__vectors_start
	B vector_
	__vectors_end
+0x200	__stubs_start
	vector_
	__stubs_end

            因此，"b vector_"  的label –PC =  offset， 而offset 为 b 指令与vector的offset，即

                         vector_-__stubs_start + ( 0x200 – ( PC_old – __vectors_start ) )

                       = vector_ + __vectors_start + 0x200 – __stubs_start – PC_old

                所以异常入口为“b vector_und + stubs_offset”, 同时stubs_offset= __vectors_start + 0x200 – __stubs_start

            我们可以通过objdump反汇编来验证：

	00000060 :     .globl    __stubs_start __stubs_start: /* * Interrupt dispatcher */     vector_stub    irq, IRQ_MODE, 4   60 :    e24ee004     sub    lr, lr, #4    ; 0x4   64:    e88d4001     stm    sp, {r0, lr} …
	1d4:    e1a00000     .word    0xe1a00000 1d8:    e1a00000     .word    0xe1a00000 1dc:    e1a00000     .word    0xe1a00000 000001e0 : /* * Undef instr entry dispatcher * Enter in UND mode, spsr = SVC/USR CPSR, lr = SVC/USR PC */ …
	__vectors_start:     swi    SYS_ERROR0 284:    ef9f0000     svc    0x009f0000     b    vector_und + stubs_offset  288:    ea0000dd     b    604     ldr    pc, .LCvswi + stubs_offset 28c:    e59ff410     ldr    pc, [pc, #1040]    ; 6a4     b    vector_pabt + stubs_offset 290:    ea0000bb     b    584     b    vector_dabt + stubs_offset 294:    ea00009a     b    504     b    vector_addrexcptn + stubs_offset 298:    ea0000fa     b    688     b    vector_irq + stubs_offset 29c:    ea000078     b    484     b    vector_fiq + stubs_offset 2a0:    ea0000f7     b    684

                              0x1e0 – 0x60 + 0x200 – ( 0x288 + 8 ) – 0x284 = 0xdd*4