text: /*
   *	Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
   *
   * This file contains the lowest level x86-specific interrupt
   * entry, irq-stacks and irq statistics code. All the remaining
   * irq logic is done by the generic kernel/irq/ code and
   * by the x86-specific irq controller code. (e.g. i8259.c and
   * io_apic.c.)
   */
  
  #include <linux/module.h>
  #include <linux/seq_file.h>
  #include <linux/interrupt.h>
  #include <linux/kernel_stat.h>
  #include <linux/notifier.h>
  #include <linux/cpu.h>
  #include <linux/delay.h>
  #include <linux/uaccess.h>
  #include <linux/percpu.h>
  #include <linux/mm.h>
  
  #include <asm/apic.h>
  
  #ifdef CONFIG_DEBUG_STACKOVERFLOW
  
  int sysctl_panic_on_stackoverflow __read_mostly;
  
  /* Debugging check for stack overflow: is there less than 1KB free? */
  static int check_stack_overflow(void)
  {
  	long sp;
  
  	__asm__ __volatile__("andl %%esp,%0" :
  			     "=r" (sp) : "0" (THREAD_SIZE - 1));
  
  	return sp < (sizeof(struct thread_info) + STACK_WARN);
  }
  
  static void print_stack_overflow(void)
  {
  	printk(KERN_WARNING "low stack detected by irq handler\n");
  	dump_stack();
  	if (sysctl_panic_on_stackoverflow)
  		panic("low stack detected by irq handler - check messages\n");
  }
  
  #else
  static inline int check_stack_overflow(void) { return 0; }
  static inline void print_stack_overflow(void) { }
  #endif
  
  DEFINE_PER_CPU(struct irq_stack *, hardirq_stack);
  DEFINE_PER_CPU(struct irq_stack *, softirq_stack);
  
  static void call_on_stack(void *func, void *stack)
  {
  	asm volatile("xchgl	%%ebx,%%esp	\n"
  		     "call	*%%edi		\n"
  		     "movl	%%ebx,%%esp	\n"
  		     : "=b" (stack)
  		     : "0" (stack),
  		       "D"(func)
  		     : "memory", "cc", "edx", "ecx", "eax");
  }
  
  static inline void *current_stack(void)
  {
  	return (void *)(current_stack_pointer() & ~(THREAD_SIZE - 1));
  }
  
  static inline int
  execute_on_irq_stack(int overflow, struct irq_desc *desc, int irq)
  {
  	struct irq_stack *curstk, *irqstk;
  	u32 *isp, *prev_esp, arg1, arg2;
  
  	curstk = (struct irq_stack *) current_stack();
  	irqstk = __this_cpu_read(hardirq_stack);
  
  	/*
  	 * this is where we switch to the IRQ stack. However, if we are
  	 * already using the IRQ stack (because we interrupted a hardirq
  	 * handler) we can't do that and just have to keep using the
  	 * current stack (which is the irq stack already after all)
  	 */
  	if (unlikely(curstk == irqstk))
  		return 0;
  
  	isp = (u32 *) ((char *)irqstk + sizeof(*irqstk));
  
  	/* Save the next esp at the bottom of the stack */
  	prev_esp = (u32 *)irqstk;
  	*prev_esp = current_stack_pointer();
  
  	if (unlikely(overflow))
  		call_on_stack(print_stack_overflow, isp);
  
  	asm volatile("xchgl	%%ebx,%%esp	\n"
  		     "call	*%%edi		\n"
  		     "movl	%%ebx,%%esp	\n"
  		     : "=a" (arg1), "=d" (arg2), "=b" (isp)
  		     :  "0" (irq),   "1" (desc),  "2" (isp),
  			"D" (desc->handle_irq)
  		     : "memory", "cc", "ecx");
  	return 1;
  }
  
  /*
   * allocate per-cpu stacks for hardirq and for softirq processing
   */
  void irq_ctx_init(int cpu)
  {
  	struct irq_stack *irqstk;
  
  	if (per_cpu(hardirq_stack, cpu))
  		return;
  
  	irqstk = page_address(alloc_pages_node(cpu_to_node(cpu),
  					       THREADINFO_GFP,
  					       THREAD_SIZE_ORDER));
  	per_cpu(hardirq_stack, cpu) = irqstk;
  
  	irqstk = page_address(alloc_pages_node(cpu_to_node(cpu),
  					       THREADINFO_GFP,
  					       THREAD_SIZE_ORDER));
  	per_cpu(softirq_stack, cpu) = irqstk;
  
  	printk(KERN_DEBUG "CPU %u irqstacks, hard=%p soft=%p\n",
  	       cpu, per_cpu(hardirq_stack, cpu),  per_cpu(softirq_stack, cpu));
  }
  
  void do_softirq_own_stack(void)
  {
  	struct thread_info *curstk;
  	struct irq_stack *irqstk;
  	u32 *isp, *prev_esp;
  
  	curstk = current_stack();
  	irqstk = __this_cpu_read(softirq_stack);
  
  	/* build the stack frame on the softirq stack */
  	isp = (u32 *) ((char *)irqstk + sizeof(*irqstk));
  
  	/* Push the previous esp onto the stack */
  	prev_esp = (u32 *)irqstk;
  	*prev_esp = current_stack_pointer();
  
  	call_on_stack(__do_softirq, isp);
  }
  
  bool handle_irq(unsigned irq, struct pt_regs *regs)
  {
  	struct irq_desc *desc;
  	int overflow;
  
  	overflow = check_stack_overflow();
  
  	desc = irq_to_desc(irq);
  	if (unlikely(!desc))
  		return false;
  
  	if (user_mode(regs) || !execute_on_irq_stack(overflow, desc, irq)) {
  		if (unlikely(overflow))
  			print_stack_overflow();
  		desc->handle_irq(irq, desc);
  	}
  
  	return true;
  }
  