今天看了 CSAPP （深入理解计算机系统）的异常控制流篇，直接来简单分析一下 Linux 内核的 中断描述符表 的初始化
源码版本：Linux kernel 5.6
内核启动时会在 start_kernel 里面调用 trap_init 去初始化中断向量表
以此为入口，开始分析
start_kernel
/init/main.c
trap_init();
trap_init
/arch/x86/kernel/traps.c
void __init trap_init(void)
{
.......
idt_setup_traps(); // 使用默认 trap（陷阱） 初始化 中断描述符表
/*
* 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() */
cea_set_pte(CPU_ENTRY_AREA_RO_IDT_VADDR, __pa_symbol(idt_table),
PAGE_KERNEL_RO);
idt_descr.address = CPU_ENTRY_AREA_RO_IDT;
/*
* Should be a barrier for any external CPU state:
*/
cpu_init();
idt_setup_ist_traps();
...........
}
idt_setup_traps
核心就在这里了
struct idt_data { // 中断描述符表 idt 的每一个表项都由一个 idt_data 结构去描述
unsigned int vector; // 中断向量
unsigned int segment; // 中断代码处于的代码段
struct idt_bits bits; // 应该是标志位
const void *addr; // 指向中断处理函数
};
#define G(_vector, _addr, _ist, _type, _dpl, _segment)
{
.vector = _vector,
.bits.ist = _ist,
.bits.type = _type,
.bits.dpl = _dpl,
.bits.p = 1,
.addr = _addr,
.segment = _segment,
}
// __KERNEL_CS 表示内核代码段
/* Interrupt gate */
// 中断陷阱
#define INTG(_vector, _addr)
G(_vector, _addr, DEFAULT_STACK, GATE_INTERRUPT, DPL0, __KERNEL_CS)
/* System interrupt gate */
// 系统中断陷阱
#define SYSG(_vector, _addr)
G(_vector, _addr, DEFAULT_STACK, GATE_INTERRUPT, DPL3, __KERNEL_CS)
/*
* Interrupt gate with interrupt stack. The _ist index is the index in
* the tss.ist[] array, but for the descriptor it needs to start at 1.
*/
// 使用中断栈（可以去看看 struct cpu_entry_area）
#define ISTG(_vector, _addr, _ist)
G(_vector, _addr, _ist + 1, GATE_INTERRUPT, DPL0, __KERNEL_CS)
/* Task gate */
// 任务陷阱
#define TSKG(_vector, _gdt)
G(_vector, NULL, DEFAULT_STACK, GATE_TASK, DPL0, _gdt << 3)
/* Interrupts/Exceptions */
// 中断向量，其实是一个 枚举，0~32 号由 intel 规定
enum {
// 除 0 异常
X86_TRAP_DE = 0, /* 0, Divide-by-zero */
// 发生调试异常
X86_TRAP_DB, /* 1, Debug */
X86_TRAP_NMI, /* 2, Non-maskable Interrupt */
// 断点（int3）
X86_TRAP_BP, /* 3, Breakpoint */
// 算术溢出
X86_TRAP_OF, /* 4, Overflow */
// 越界访问
X86_TRAP_BR, /* 5, Bound Range Exceeded */
// cpu 执行到无效操作码
X86_TRAP_UD, /* 6, Invalid Opcode */
// 在 没有 浮点运算单元 时（或者设置了 cr0 的标志位标识 FPU/MMX/SSE 不可用）进行浮点运算
X86_TRAP_NM, /* 7, Device Not Available */
// 双重异常（比如在发生异常后调用异常处理函数时又触发了异常）
X86_TRAP_DF, /* 8, Double Fault */
X86_TRAP_OLD_MF, /* 9, Coprocessor Segment Overrun */
// TSS 无效
X86_TRAP_TS, /* 10, Invalid TSS */
X86_TRAP_NP, /* 11, Segment Not Present */
X86_TRAP_SS, /* 12, Stack Segment Fault */
X86_TRAP_GP, /* 13, General Protection Fault */
// 缺页
X86_TRAP_PF, /* 14, Page Fault */
X86_TRAP_SPURIOUS, /* 15, Spurious Interrupt */
X86_TRAP_MF, /* 16, x87 Floating-Point Exception */
X86_TRAP_AC, /* 17, Alignment Check */
X86_TRAP_MC, /* 18, Machine Check */
X86_TRAP_XF, /* 19, SIMD Floating-Point Exception */
X86_TRAP_IRET = 32, /* 32, IRET Exception */
};
/*
* The default IDT entries which are set up in trap_init() before
* cpu_init() is invoked. Interrupt stacks cannot be used at that point and
* the traps which use them are reinitialized with IST after cpu_init() has
* set up TSS.
*/
static const __initconst struct idt_data def_idts[] = {
// 每一个 INTG 就是设置一个 idt_data 表项（第一个参数是中断向量）
INTG(X86_TRAP_DE, divide_error),
INTG(X86_TRAP_NMI, nmi),
INTG(X86_TRAP_BR, bounds),
INTG(X86_TRAP_UD, invalid_op),
INTG(X86_TRAP_NM, device_not_available),
INTG(X86_TRAP_OLD_MF, coprocessor_segment_overrun),
INTG(X86_TRAP_TS, invalid_TSS),
INTG(X86_TRAP_NP, segment_not_present),
INTG(X86_TRAP_SS, stack_segment),
INTG(X86_TRAP_GP, general_protection),
INTG(X86_TRAP_SPURIOUS, spurious_interrupt_bug),
INTG(X86_TRAP_MF, coprocessor_error),
INTG(X86_TRAP_AC, alignment_check),
INTG(X86_TRAP_XF, simd_coprocessor_error),
#ifdef CONFIG_X86_32
TSKG(X86_TRAP_DF, GDT_ENTRY_DOUBLEFAULT_TSS),
#else
INTG(X86_TRAP_DF, double_fault),
#endif
INTG(X86_TRAP_DB, debug),
#ifdef CONFIG_X86_MCE
INTG(X86_TRAP_MC, &machine_check),
#endif
SYSG(X86_TRAP_OF, overflow),
#if defined(CONFIG_IA32_EMULATION)
SYSG(IA32_SYSCALL_VECTOR, entry_INT80_compat),
#elif defined(CONFIG_X86_32)
SYSG(IA32_SYSCALL_VECTOR, entry_INT80_32), // x86_32 的系统调用 int 0x80
#endif
};
/**
* idt_setup_traps - Initialize the idt table with default traps
*/
void __init idt_setup_traps(void)
{
// 使用预设的 def_idts 来设置 中断描述符表 idt_table
idt_setup_from_table(idt_table, def_idts, ARRAY_SIZE(def_idts), true);
}
| Name | Vector nr. | Type | Mnemonic | Error code? |
|---|---|---|---|---|
| Divide-by-zero Error | 0 (0x0) | Fault | #DE | No |
| Debug | 1 (0x1) | Fault/Trap | #DB | No |
| Non-maskable Interrupt | 2 (0x2) | Interrupt | - | No |
| Breakpoint | 3 (0x3) | Trap | #BP | No |
| Overflow | 4 (0x4) | Trap | #OF | No |
| Bound Range Exceeded | 5 (0x5) | Fault | #BR | No |
| Invalid Opcode | 6 (0x6) | Fault | #UD | No |
| Device Not Available | 7 (0x7) | Fault | #NM | No |
| Double Fault | 8 (0x8) | Abort | #DF | Yes (Zero) |
| 9 (0x9) | Fault | - | No | |
| Invalid TSS | 10 (0xA) | Fault | #TS | Yes |
| Segment Not Present | 11 (0xB) | Fault | #NP | Yes |
| Stack-Segment Fault | 12 (0xC) | Fault | #SS | Yes |
| General Protection Fault | 13 (0xD) | Fault | #GP | Yes |
| Page Fault | 14 (0xE) | Fault | #PF | Yes |
| Reserved | 15 (0xF) | - | - | No |
| x87 Floating-Point Exception | 16 (0x10) | Fault | #MF | No |
| Alignment Check | 17 (0x11) | Fault | #AC | Yes |
| Machine Check | 18 (0x12) | Abort | #MC | No |
| SIMD Floating-Point Exception | 19 (0x13) | Fault | #XM/#XF | No |
| Virtualization Exception | 20 (0x14) | Fault | #VE | No |
| Reserved | 21-29 (0x15-0x1D) | - | - | No |
| Security Exception | 30 (0x1E) | - | #SX | Yes |
| Reserved | 31 (0x1F) | - | - | No |
| Triple Fault | - | - | - | No |
| IRQ 13 | Interrupt | #FERR | No |
static inline void idt_init_desc(gate_desc *gate, const struct idt_data *d)
{
unsigned long addr = (unsigned long) d->addr;
gate->offset_low = (u16) addr;
gate->segment = (u16) d->segment;
gate->bits = d->bits;
gate->offset_middle = (u16) (addr >> 16);
#ifdef CONFIG_X86_64
gate->offset_high = (u32) (addr >> 32);
gate->reserved = 0;
#endif
}
#define write_idt_entry(dt, entry, g) native_write_idt_entry(dt, entry, g)
static inline void native_write_idt_entry(gate_desc *idt, int entry, const gate_desc *gate)
{
memcpy(&idt[entry], gate, sizeof(*gate));
}
static void
idt_setup_from_table(gate_desc *idt, const struct idt_data *t, int size, bool sys)
{
gate_desc desc;
// 循环拷贝每个表项
for (; size > 0; t++, size--) {
idt_init_desc(&desc, t); // 把每个表项的数据拷贝到 desc
write_idt_entry(idt, t->vector, &desc); // 直接使用 memcpy 拷贝，t->vector 就是 对应 desc 的中断向量，拷贝到对应的 idt 的中断向量是 t->vector 的表项
if (sys)
set_bit(t->vector, system_vectors);
}
}
总结
其实开机时初始化中断描述符表（idt_table）就是从默认的描述符表（def_idts）拷贝需要的表项