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

    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(X86_TRAP_SS, stack_segment);
    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:
    将前32个中断号都设置为已使用状态
     */
    for (i = 0; i < FIRST_EXTERNAL_VECTOR; i++)
        set_bit(i, used_vectors);
    //设置0x80系统调用的系统中断门
#ifdef CONFIG_IA32_EMULATION
    set_system_intr_gate(IA32_SYSCALL_VECTOR, entry_INT80_compat);
    set_bit(IA32_SYSCALL_VECTOR, used_vectors);
#endif

#ifdef CONFIG_X86_32
    set_system_intr_gate(IA32_SYSCALL_VECTOR, entry_INT80_32);
    set_bit(IA32_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:
     执行CPU的初始化，对于中断而言，在 cpu_init() 中主要是将 idt_descr 放入idtr寄存器中
     */
    cpu_init();

    /*
     * X86_TRAP_DB and X86_TRAP_BP have been set
     * in early_trap_init(). However, ITS works only after
     * cpu_init() loads TSS. See comments in early_trap_init().
     */
    set_intr_gate_ist(X86_TRAP_DB, &debug, DEBUG_STACK);
    /* int3 can be called from all */
    set_system_intr_gate_ist(X86_TRAP_BP, &int3, DEBUG_STACK);

    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
}

/* May run on IST stack. */
dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
{
#ifdef CONFIG_DYNAMIC_FTRACE
    /*
     * ftrace must be first, everything else may cause a recursive crash.
     * See note by declaration of modifying_ftrace_code in ftrace.c
     */
    if (unlikely(atomic_read(&modifying_ftrace_code)) &&
        ftrace_int3_handler(regs))
        return;
#endif
    if (poke_int3_handler(regs))
        return;

    ist_enter(regs);
    RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
    if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
                SIGTRAP) == NOTIFY_STOP)
        goto exit;
#endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */

#ifdef CONFIG_KPROBES
    if (kprobe_int3_handler(regs))
        goto exit;
#endif

    if (notify_die(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
            SIGTRAP) == NOTIFY_STOP)
        goto exit;

    /*
     * Let others (NMI) know that the debug stack is in use
     * as we may switch to the interrupt stack.
     */
    debug_stack_usage_inc();
    preempt_disable();
    cond_local_irq_enable(regs);
    do_trap(X86_TRAP_BP, SIGTRAP, "int3", regs, error_code, NULL);//核心代码
    cond_local_irq_disable(regs);
    preempt_enable_no_resched();
    debug_stack_usage_dec();
exit:
    ist_exit(regs);
}

/* Call softirq on interrupt stack. Interrupts are off. */
ENTRY(do_softirq_own_stack)
    pushq    %rbp
    mov    %rsp, %rbp
    incl    PER_CPU_VAR(irq_count)
    cmove    PER_CPU_VAR(irq_stack_ptr), %rsp
    push    %rbp                /* frame pointer backlink */
    call    __do_softirq
    leaveq
    decl    PER_CPU_VAR(irq_count)
    ret
END(do_softirq_own_stack)

└─# strace cat 1.txt
execve("/usr/bin/cat", ["cat", "1.txt"], 0x7ffd36672918 /* 51 vars */) = 0
brk(NULL)                               = 0x55cbf772d000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=94692, ...}) = 0
mmap(NULL, 94692, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fc9c4d5e000
close(3)                                = 0
openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0@n\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1839792, ...}) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc9c4d5c000
mmap(NULL, 1852680, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc9c4b97000
mprotect(0x7fc9c4bbc000, 1662976, PROT_NONE) = 0
mmap(0x7fc9c4bbc000, 1355776, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x25000) = 0x7fc9c4bbc000
mmap(0x7fc9c4d07000, 303104, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x170000) = 0x7fc9c4d07000
mmap(0x7fc9c4d52000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1ba000) = 0x7fc9c4d52000
mmap(0x7fc9c4d58000, 13576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fc9c4d58000
close(3)                                = 0
arch_prctl(ARCH_SET_FS, 0x7fc9c4d5d580) = 0
mprotect(0x7fc9c4d52000, 12288, PROT_READ) = 0
mprotect(0x55cbf6e3e000, 4096, PROT_READ) = 0
mprotect(0x7fc9c4da0000, 4096, PROT_READ) = 0
munmap(0x7fc9c4d5e000, 94692)           = 0
brk(NULL)                               = 0x55cbf772d000
brk(0x55cbf774e000)                     = 0x55cbf774e000
openat(AT_FDCWD, "/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=3041456, ...}) = 0
mmap(NULL, 3041456, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fc9c48b0000
close(3)                                = 0
fstat(1, {st_mode=S_IFCHR|0600, st_rdev=makedev(0x88, 0), ...}) = 0
openat(AT_FDCWD, "1.txt", O_RDONLY)     = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=5, ...}) = 0
fadvise64(3, 0, 0, POSIX_FADV_SEQUENTIAL) = 0
mmap(NULL, 139264, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc9c488e000
read(3, "11111", 131072)                = 5
write(1, "11111", 511111)                    = 5
read(3, "", 131072)                     = 0                                                                        
munmap(0x7fc9c488e000, 139264)          = 0
close(3)                                = 0
close(1)                                = 0
close(2)                                = 0
exit_group(0)                           = ?
+++ exited with 0 +++