一．ARM linux的中斷向量表初始化分析
ARM linux內核啟動時，通過start_kernel()->trap_init()的調用關系，初始化內核的中斷異常向量表．
／* arch/arm/kernel/traps.c */
void __init trap_init(void)
{
extern void __trap_init(unsigned long);
unsigned long base = vectors_base();
__trap_init(base);
if (base != 0)
oopsprintk(KERN_DEBUG "Relocating machine vectors to 0x%08lx\\n", base);
#ifdef CONFIG_CPU_32
modify_domain(DOMAIN_USER, DOMAIN_CLIENT);
#endif
}
vectors_base是一個宏，它的作用是獲取ARM異常向量的地址，該宏在include/arch/asm-arm/proc-armv/system.h中定義：
extern unsigned long cr_no_alignment; /* defined in entry-armv.S */
extern unsigned long cr_alignment; /* defined in entry-armv.S */
#if __LINUX_ARM_ARCH__ >= 4
#define vectors_base() ((cr_alignment & CR_V) ? 0xffff0000 : 0)
#else
#define vectors_base() (0)
#endif
對于ARMv4以下的版本，這個地址固定為0；ARMv4及其以上的版本，ARM異常向量表的地址受協處理器CP15的c1寄存器(control register)中V位(bit[13])的控制，如果V=1，則異常向量表的地址為0x00000000~0x0000001C；如果V=0,則為:0xffff0000~0xffff001C。（詳情請參考ARM Architecture Reference Manual)
下面分析一下cr_alginment的值是在哪確定的，我們在arch/arm/kernel/entry-armv.S找到cr_alignment的定義：
.globl SYMBOL_NAME(cr_alignment)
.globl SYMBOL_NAME(cr_no_alignment)
SYMBOL_NAME(cr_alignment):
.space 4
SYMBOL_NAME(cr_no_alignment):
.space 4
分析過head-armv.S文件的朋友都會知道，head-armv.S是非壓縮內核的入口：
１ .section ".text.init",#alloc,#execinstr
２ .type stext, #function
３ENTRY(stext)
４ mov r12, r0
５
６ mov r0, #F_BIT | I_BIT | MODE_SVC @ make sure svc mode
７ msr cpsr_c, r0 @ and all irqs disabled
８ bl __lookup_processor_type
９ teq r10, #0 @ invalid processor?
10 moveq r0, #\'p\' @ yes, error \'p\'
11 beq __error
12 bl __lookup_architecture_type
13 teq r7, #0 @ invalid architecture?
14 moveq r0, #\'a\' @ yes, error \'a\'
15 beq __error
16 bl __create_page_tables
17 adr lr, __ret @ return address
18 add pc, r10, #12 @ initialise processor
19 @ (return control reg)
20
21 .type __switch_data, %object
22__switch_data: .long __mmap_switched
23 .long SYMBOL_NAME(__bss_start)
24 .long SYMBOL_NAME(_end)
25 .long SYMBOL_NAME(processor_id)
26 .long SYMBOL_NAME(__machine_arch_type)
27 .long SYMBOL_NAME(cr_alignment)
28 .long SYMBOL_NAME(init_task_union)+8192
29
30 .type __ret, %function
31__ret: ldr lr, __switch_data
32 mcr p15, 0, r0, c1, c0
33 mrc p15, 0, r0, c1, c0, 0 @ read it back.
34 mov r0, r0
35 mov r0, r0
36 mov pc, lr
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