时钟中断TIMER_BH(bottom_half)实现分析

时钟中断TIMER_BH(bottom_half)实现分析
1.3.100
1. 时钟0号中断安装
    setup_x86_irq(0, &irq0);@arch/i386/kernel/time.c
        |- set_intr_gate(0x20+irq,interrupt[irq]);//interrupt[0]=IRQ0_interrupt
        
        附：IRQ0_interrupt宏函数定义：BUILD_TIMER_IRQ(FIRST,0,0x01)

        #define BUILD_TIMER_IRQ(chip,nr,mask)
asmlinkage void IRQ_NAME(nr);
asmlinkage void FAST_IRQ_NAME(nr);
asmlinkage void BAD_IRQ_NAME(nr);
__asm__(
" "__ALIGN_STR" "
SYMBOL_NAME_STR(fast_IRQ) #nr "_interrupt: "
SYMBOL_NAME_STR(bad_IRQ) #nr "_interrupt: "
SYMBOL_NAME_STR(IRQ) #nr "_interrupt: "
    "pushl $-"#nr"-2 "
    SAVE_ALL
    ACK_##chip(mask)
    "incl "SYMBOL_NAME_STR(intr_count)" "
    "movl %esp,%ebx "
    "pushl %ebx "
    "pushl $" #nr " "
    "call "SYMBOL_NAME_STR(do_IRQ)" "
    "addl $8,%esp "
    "cli "
    UNBLK_##chip(mask)
    "decl "SYMBOL_NAME_STR(intr_count)" "
    "jmp ret_from_sys_call ");
        
       
2. 时钟中断调用
    IRQ0_interrupt->do_IRQ->timer_interrupt->do_timer
     ->ret_from_sys_call->handle_bottom_half->do_bottom_half@kernel/softirq.c
    
    
另1：do_bottom_half会开启中断
asmlinkage void do_bottom_half(void)
{
    unsigned long active;
    unsigned long mask, left;
    void (**bh)(void);

    sti();
    bh = bh_base;
    active = bh_active & bh_mask;
    for (mask = 1, left = ~0 ; left & active ; bh++,mask += mask,left += left) {
        if (mask & active) {
            void (*fn)(void);
            bh_active &= ~mask;
            fn = *bh;
            if (!fn)
                goto bad_bh;
            fn();
        }
    }
    return;
bad_bh:
    printk ("irq.c:bad bottom half entry %08lx ", mask);
}



    
另2：ret_from_sys_call段如下：
handle_bottom_half:
    incl SYMBOL_NAME(intr_count)
    call SYMBOL_NAME(do_bottom_half)
    decl SYMBOL_NAME(intr_count)
    jmp 9f
    
...
     ret_from_sys_call:
    cmpl $0,SYMBOL_NAME(intr_count)
    jne 2f
9:    movl SYMBOL_NAME(bh_mask),%eax
    andl SYMBOL_NAME(bh_active),%eax
    jne handle_bottom_half
    movl EFLAGS(%esp),%eax        # check VM86 flag: CS/SS are
    testl $(VM_MASK),%eax        # different then
    jne 1f
    cmpw $(KERNEL_CS),CS(%esp)    # was old code segment supervisor ?
    je 2f
1:    sti
    orl $(IF_MASK),%eax        # these just try to make sure
    andl $~NT_MASK,%eax        # the program doesn't do anything
    movl %eax,EFLAGS(%esp)        # stupid
    cmpl $0,SYMBOL_NAME(need_resched)
    jne reschedule
#ifdef __SMP__
    GET_PROCESSOR_OFFSET(%eax)
    movl SYMBOL_NAME(current_set)(,%eax), %eax
#else
    movl SYMBOL_NAME(current_set),%eax
#endif
    cmpl SYMBOL_NAME(task),%eax    # task[0] cannot have signals
    je 2f
    movl blocked(%eax),%ecx
    movl %ecx,%ebx            # save blocked in %ebx for signal handling
    notl %ecx
    andl signal(%eax),%ecx
    jne signal_return
2:    RESTORE_ALL