init_ir_技术实现篇

1. 中断的初始化

中断向量号是8位的，那么它一共有256项(0-255)，所以中断描述符表最多只有256项，中断向量表也是256项。

对于不同的中断，在中断初始化和中断处理过程中，其处理方式是不一样的，尤其是不同类型的中断，其处理响应机制差别较大，后面会详述。这里先描述中断的初始化过程。

从中断触发的源角度，可以将中断分为内部中断（0~31号中断向量号）和外部中断（32~255号中断向量号），linux初始化过程中，会先初始化内部中断，再初始化外部中断。这两种中断的初始化区别如下：

1. 内部中断(0~31号、0x80作为中断号)
只要初始化:
    1) 相关的中断向量表
2. 外部中断(0~255中的除了0~31号、0x80的其他中断号)
需要初始化:
    1) 相关的中断向量表
    2) 以及中断控制器(控制器负责优先级排队、屏蔽等工作)

0x1: 内部中断初始化

内部中断的初始化需要对0~31号和0x80号系统保留中断向量的初始化，这部分草走在trap_init()中完成

linux-3.15.5archx86kernel raps

void __init trap_init(void)
{
    int i;

#ifdef CONFIG_EISA
    void __iomem *p = early_ioremap(0x0FFFD9, 4);

    if (readl(p) == 'E' + ('I'<<8) + ('S'<<16) + ('A'<<24))
        EISA_bus = 1;
    early_iounmap(p, 4);
#endif
/*
trap_init()主要是调用set_xxx_gate(中断向量, 中断处理函数)
set_xxx_gate()就是按照中断门的格式填写中断向量表的

Intel x86支持4种"门描述符":
1) 调用门(call gate) 
2) 陷阱门(trap gate)   
3) 中断门(iinterrupt gate)   
4) 任务门(task gate)
*/
    set_intr_gate(X86_TRAP_DE, divide_error);
    set_intr_gate_ist(X86_TRAP_NMI, &nmi, NMI_STACK);
    /* int4 can be called from all */
    set_system_intr_gate(X86_TRAP_OF, &overflow);
    set_intr_gate(X86_TRAP_BR, bounds);
    set_intr_gate(X86_TRAP_UD, invalid_op);
    set_intr_gate(X86_TRAP_NM, device_not_available);
#ifdef CONFIG_X86_32
    set_task_gate(X86_TRAP_DF, GDT_ENTRY_DOUBLEFAULT_TSS);
#else
    set_intr_gate_ist(X86_TRAP_DF, &double_fault, DOUBLEFAULT_STACK);
#endif
    set_intr_gate(X86_TRAP_OLD_MF, coprocessor_segment_overrun);
    set_intr_gate(X86_TRAP_TS, invalid_TSS);
    set_intr_gate(X86_TRAP_NP, segment_not_present);
    set_intr_gate_ist(X86_TRAP_SS, &stack_segment, STACKFAULT_STACK);
    set_intr_gate(X86_TRAP_GP, general_protection);
    set_intr_gate(X86_TRAP_SPURIOUS, spurious_interrupt_bug);
    set_intr_gate(X86_TRAP_MF, coprocessor_error);
    set_intr_gate(X86_TRAP_AC, alignment_check);
#ifdef CONFIG_X86_MCE
    set_intr_gate_ist(X86_TRAP_MC, &machine_check, MCE_STACK);
#endif
    set_intr_gate(X86_TRAP_XF, simd_coprocessor_error);

    /* Reserve all the builtin and the syscall vector: */
    for (i = 0; i < FIRST_EXTERNAL_VECTOR; i++)
        set_bit(i, used_vectors);

#ifdef CONFIG_IA32_EMULATION
    set_system_intr_gate(IA32_SYSCALL_VECTOR, ia32_syscall);
    set_bit(IA32_SYSCALL_VECTOR, used_vectors);
#endif
//设置系统调用中断
#ifdef CONFIG_X86_32
    set_system_trap_gate(SYSCALL_VECTOR, &system_call);
    set_bit(SYSCALL_VECTOR, used_vectors);
#endif

    /*
     * Set the IDT descriptor to a fixed read-only location, so that the
     * "sidt" instruction will not leak the location of the kernel, and
     * to defend the IDT against arbitrary memory write vulnerabilities.
     * It will be reloaded in cpu_init() */
    __set_fixmap(FIX_RO_IDT, __pa_symbol(idt_table), PAGE_KERNEL_RO);
    idt_descr.address = fix_to_virt(FIX_RO_IDT);

    /*
     * Should be a barrier for any external CPU state:
     */
    cpu_init();

    x86_init.irqs.trap_init();

#ifdef CONFIG_X86_64
    memcpy(&debug_idt_table, &idt_table, IDT_ENTRIES * 16);
    set_nmi_gate(X86_TRAP_DB, &debug);
    set_nmi_gate(X86_TRAP_BP, &int3);
#endif
}

0x2: 外部中断初始化

外部中断的初始化需要:

1. 对除了0~31、0x80中断号之外的其它中断向量
2. 中断控制器的初始化(相比内部中断初始化多了这一步)
这两步操作都在在init_IRQ()中完成

linux-3.15.5archx86kerneli8259.c

void __init init_IRQ(void)
{
    int i;

    /*
     * We probably need a better place for this, but it works for
     * now ...
     */
    x86_add_irq_domains();

    /*
     * On cpu 0, Assign IRQ0_VECTOR..IRQ15_VECTOR's to IRQ 0..15.
     * If these IRQ's are handled by legacy interrupt-controllers like PIC,
     * then this configuration will likely be static after the boot. If
     * these IRQ's are handled by more mordern controllers like IO-APIC,
     * then this vector space can be freed and re-used dynamically as the
     * irq's migrate etc.
     */
    for (i = 0; i < legacy_pic->nr_legacy_irqs; i++) //对于单CPU结构，
        per_cpu(vector_irq, 0)[IRQ0_VECTOR + i] = i;

    //x86_init.irqs.intr_init()等价于调用：native_init_IRQ()
    x86_init.irqs.intr_init();
}


void __init native_init_IRQ(void)
{
    int i;

    /* Execute any quirks before the call gates are initialised: */
    x86_init.irqs.pre_vector_init(); //调用 init_ISA_irqs 

    apic_intr_init();  

    /*
     * Cover the whole vector space, no vector can escape
     * us. (some of these will be overridden and become
     * 'special' SMP interrupts)
     */
     /*
     interrupt数组，它保存的是每个中断服务程序的入口地址，它的定义是在linux-3.15.5archx86kernelentry_32.S中
     */
    for (i = FIRST_EXTERNAL_VECTOR; i < NR_VECTORS; i++) 
    { 
    //设置32~255号中断
        /* IA32_SYSCALL_VECTOR could be used in trap_init already. */
        if (!test_bit(i, used_vectors)) 
    {
        //要除去0x80中断
        set_intr_gate(i, interrupt[i-FIRST_EXTERNAL_VECTOR]);
    } 
    }


    if (!acpi_ioapic && !of_ioapic)
        setup_irq(2, &irq2);

#ifdef CONFIG_X86_32
    /*
     * External FPU? Set up irq13 if so, for
     * original braindamaged IBM FERR coupling.
     */
    if (boot_cpu_data.hard_math && !cpu_has_fpu)
        setup_irq(FPU_IRQ, &fpu_irq);

    irq_ctx_init(smp_processor_id());
#endif
}