ARM处理器模式弹跳机制的初始化 笔记版 转载请注明出处[e-mail]

void cpu_init(void)
{
unsigned int cpu = smp_processor_id();
struct stack *stk = &stacks[cpu];


if (cpu >= NR_CPUS) {
printk(KERN_CRIT "CPU%u: bad primary CPU number\n", cpu);
BUG();
}


/*
* Define the placement constraint for the inline asm directive below.
* In Thumb-2, msr with an immediate value is not allowed.
*/
#ifdef CONFIG_THUMB2_KERNEL
#define PLC "r"
#else
#define PLC "I"
#endif


/*
* setup stacks for re-entrant exception handlers
*/
__asm__ (
"msr cpsr_c, %1\n\t"
"add r14, %0, %2\n\t"
"mov sp, r14\n\t"
"msr cpsr_c, %3\n\t"
"add r14, %0, %4\n\t"
"mov sp, r14\n\t"
"msr cpsr_c, %5\n\t"
"add r14, %0, %6\n\t"
"mov sp, r14\n\t"
"msr cpsr_c, %7"
   :
   : "r" (stk),
     PLC (PSR_F_BIT | PSR_I_BIT | IRQ_MODE),
     "I" (offsetof(struct stack, irq[0])),
     PLC (PSR_F_BIT | PSR_I_BIT | ABT_MODE),
     "I" (offsetof(struct stack, abt[0])),
     PLC (PSR_F_BIT | PSR_I_BIT | UND_MODE),
     "I" (offsetof(struct stack, und[0])),
     PLC (PSR_F_BIT | PSR_I_BIT | SVC_MODE)
   : "r14");
}

依次进入arm的IRQ、ABT、UND模式，每进到一种模式CPU就看到了自己在这个模式下的SP寄存器，然后将这个栈指针指向实现准备好一块内存，stacks[cpu]为这些模式准备了相应的栈，虽然很小，但足够了，因为对于这些模式ARM是蜻蜓点水，刚进去就跳出来。