src/arch/x86/exception.c

/*
 * This file is part of the coreboot project.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2 of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#include <arch/cpu.h>
#include <arch/early_variables.h>
#include <arch/exception.h>
#include <commonlib/helpers.h>
#include <console/console.h>
#include <console/streams.h>
#include <cpu/x86/cr.h>
#include <cpu/x86/lapic.h>
#include <stdint.h>
#include <string.h>

#if IS_ENABLED(CONFIG_GDB_STUB)

/* BUFMAX defines the maximum number of characters in inbound/outbound buffers.
 * At least NUM_REGBYTES*2 are needed for register packets
 */
#define BUFMAX 400
enum regnames {
	EAX = 0, ECX, EDX, EBX, ESP, EBP, ESI, EDI,
	PC /* also known as eip */,
	PS /* also known as eflags */,
	CS, SS, DS, ES, FS, GS,
	NUM_REGS /* Number of registers. */
};

static uint32_t gdb_stub_registers[NUM_REGS];

#define GDB_SIG0         0     /* Signal 0 */
#define GDB_SIGHUP       1     /* Hangup */
#define GDB_SIGINT       2     /* Interrupt */
#define GDB_SIGQUIT      3     /* Quit */
#define GDB_SIGILL       4     /* Illegal instruction */
#define GDB_SIGTRAP      5     /* Trace/breakpoint trap */
#define GDB_SIGABRT      6     /* Aborted */
#define GDB_SIGEMT       7     /* Emulation trap */
#define GDB_SIGFPE       8     /* Arithmetic exception */
#define GDB_SIGKILL      9     /* Killed */
#define GDB_SIGBUS       10    /* Bus error */
#define GDB_SIGSEGV      11    /* Segmentation fault */
#define GDB_SIGSYS       12    /* Bad system call */
#define GDB_SIGPIPE      13    /* Broken pipe */
#define GDB_SIGALRM      14    /* Alarm clock */
#define GDB_SIGTERM      15    /* Terminated */
#define GDB_SIGURG       16    /* Urgent I/O condition */
#define GDB_SIGSTOP      17    /* Stopped (signal) */
#define GDB_SIGTSTP      18    /* Stopped (user) */
#define GDB_SIGCONT      19    /* Continued */
#define GDB_SIGCHLD      20    /* Child status changed */
#define GDB_SIGTTIN      21    /* Stopped (tty input) */
#define GDB_SIGTTOU      22    /* Stopped (tty output) */
#define GDB_SIGIO        23    /* I/O possible */
#define GDB_SIGXCPU      24    /* CPU time limit exceeded */
#define GDB_SIGXFSZ      25    /* File size limit exceeded */
#define GDB_SIGVTALRM    26    /* Virtual timer expired */
#define GDB_SIGPROF      27    /* Profiling timer expired */
#define GDB_SIGWINCH     28    /* Window size changed */
#define GDB_SIGLOST      29    /* Resource lost */
#define GDB_SIGUSR1      30    /* User defined signal 1 */
#define GDB_SUGUSR2      31    /* User defined signal 2 */
#define GDB_SIGPWR       32    /* Power fail/restart */
#define GDB_SIGPOLL      33    /* Pollable event occurred */
#define GDB_SIGWIND      34    /* SIGWIND */
#define GDB_SIGPHONE     35    /* SIGPHONE */
#define GDB_SIGWAITING   36    /* Process's LWPs are blocked */
#define GDB_SIGLWP       37    /* Signal LWP */
#define GDB_SIGDANGER    38    /* Swap space dangerously low */
#define GDB_SIGGRANT     39    /* Monitor mode granted */
#define GDB_SIGRETRACT   40    /* Need to relinquish monitor mode */
#define GDB_SIGMSG       41    /* Monitor mode data available */
#define GDB_SIGSOUND     42    /* Sound completed */
#define GDB_SIGSAK       43    /* Secure attention */
#define GDB_SIGPRIO      44    /* SIGPRIO */

#define GDB_SIG33        45    /* Real-time event 33 */
#define GDB_SIG34        46    /* Real-time event 34 */
#define GDB_SIG35        47    /* Real-time event 35 */
#define GDB_SIG36        48    /* Real-time event 36 */
#define GDB_SIG37        49    /* Real-time event 37 */
#define GDB_SIG38        50    /* Real-time event 38 */
#define GDB_SIG39        51    /* Real-time event 39 */
#define GDB_SIG40        52    /* Real-time event 40 */
#define GDB_SIG41        53    /* Real-time event 41 */
#define GDB_SIG42        54    /* Real-time event 42 */
#define GDB_SIG43        55    /* Real-time event 43 */
#define GDB_SIG44        56    /* Real-time event 44 */
#define GDB_SIG45        57    /* Real-time event 45 */
#define GDB_SIG46        58    /* Real-time event 46 */
#define GDB_SIG47        59    /* Real-time event 47 */
#define GDB_SIG48        60    /* Real-time event 48 */
#define GDB_SIG49        61    /* Real-time event 49 */
#define GDB_SIG50        62    /* Real-time event 50 */
#define GDB_SIG51        63    /* Real-time event 51 */
#define GDB_SIG52        64    /* Real-time event 52 */
#define GDB_SIG53        65    /* Real-time event 53 */
#define GDB_SIG54        66    /* Real-time event 54 */
#define GDB_SIG55        67    /* Real-time event 55 */
#define GDB_SIG56        68    /* Real-time event 56 */
#define GDB_SIG57        69    /* Real-time event 57 */
#define GDB_SIG58        70    /* Real-time event 58 */
#define GDB_SIG59        71    /* Real-time event 59 */
#define GDB_SIG60        72    /* Real-time event 60 */
#define GDB_SIG61        73    /* Real-time event 61 */
#define GDB_SIG62        74    /* Real-time event 62 */
#define GDB_SIG63        75    /* Real-time event 63 */
#define GDB_SIGCANCEL    76    /* LWP internal signal */
#define GDB_SIG32        77    /* Real-time event 32 */
#define GDB_SIG64        78    /* Real-time event 64 */
#define GDB_SIG65        79    /* Real-time event 65 */
#define GDB_SIG66        80    /* Real-time event 66 */
#define GDB_SIG67        81    /* Real-time event 67 */
#define GDB_SIG68        82    /* Real-time event 68 */
#define GDB_SIG69        83    /* Real-time event 69 */
#define GDB_SIG70        84    /* Real-time event 70 */
#define GDB_SIG71        85    /* Real-time event 71 */
#define GDB_SIG72        86    /* Real-time event 72 */
#define GDB_SIG73        87    /* Real-time event 73 */
#define GDB_SIG74        88    /* Real-time event 74 */
#define GDB_SIG75        89    /* Real-time event 75 */
#define GDB_SIG76        90    /* Real-time event 76 */
#define GDB_SIG77        91    /* Real-time event 77 */
#define GDB_SIG78        92    /* Real-time event 78 */
#define GDB_SIG79        93    /* Real-time event 79 */
#define GDB_SIG80        94    /* Real-time event 80 */
#define GDB_SIG81        95    /* Real-time event 81 */
#define GDB_SIG82        96    /* Real-time event 82 */
#define GDB_SIG83        97    /* Real-time event 83 */
#define GDB_SIG84        98    /* Real-time event 84 */
#define GDB_SIG85        99    /* Real-time event 85 */
#define GDB_SIG86       100    /* Real-time event 86 */
#define GDB_SIG87       101    /* Real-time event 87 */
#define GDB_SIG88       102    /* Real-time event 88 */
#define GDB_SIG89       103    /* Real-time event 89 */
#define GDB_SIG90       104    /* Real-time event 90 */
#define GDB_SIG91       105    /* Real-time event 91 */
#define GDB_SIG92       106    /* Real-time event 92 */
#define GDB_SIG93       107    /* Real-time event 93 */
#define GDB_SIG94       108    /* Real-time event 94 */
#define GDB_SIG95       109    /* Real-time event 95 */
#define GDB_SIG96       110    /* Real-time event 96 */
#define GDB_SIG97       111    /* Real-time event 97 */
#define GDB_SIG98       112    /* Real-time event 98 */
#define GDB_SIG99       113    /* Real-time event 99 */
#define GDB_SIG100      114    /* Real-time event 100 */
#define GDB_SIG101      115    /* Real-time event 101 */
#define GDB_SIG102      116    /* Real-time event 102 */
#define GDB_SIG103      117    /* Real-time event 103 */
#define GDB_SIG104      118    /* Real-time event 104 */
#define GDB_SIG105      119    /* Real-time event 105 */
#define GDB_SIG106      120    /* Real-time event 106 */
#define GDB_SIG107      121    /* Real-time event 107 */
#define GDB_SIG108      122    /* Real-time event 108 */
#define GDB_SIG109      123    /* Real-time event 109 */
#define GDB_SIG110      124    /* Real-time event 110 */
#define GDB_SIG111      125    /* Real-time event 111 */
#define GDB_SIG112      126    /* Real-time event 112 */
#define GDB_SIG113      127    /* Real-time event 113 */
#define GDB_SIG114      128    /* Real-time event 114 */
#define GDB_SIG115      129    /* Real-time event 115 */
#define GDB_SIG116      130    /* Real-time event 116 */
#define GDB_SIG117      131    /* Real-time event 117 */
#define GDB_SIG118      132    /* Real-time event 118 */
#define GDB_SIG119      133    /* Real-time event 119 */
#define GDB_SIG120      134    /* Real-time event 120 */
#define GDB_SIG121      135    /* Real-time event 121 */
#define GDB_SIG122      136    /* Real-time event 122 */
#define GDB_SIG123      137    /* Real-time event 123 */
#define GDB_SIG124      138    /* Real-time event 124 */
#define GDB_SIG125      139    /* Real-time event 125 */
#define GDB_SIG126      140    /* Real-time event 126 */
#define GDB_SIG127      141    /* Real-time event 127 */
#define GDB_SIGINFO     142    /* Information request */
#define GDB_UNKNOWN     143    /* Unknown signal */
#define GDB_DEFAULT     144    /* error: default signal */
/* Mach exceptions */
#define GDB_EXC_BAD_ACCESS     145 /* Could not access memory */
#define GDB_EXC_BAD_INSTRCTION 146 /* Illegal instruction/operand */
#define GDB_EXC_ARITHMETIC     147 /* Arithmetic exception */
#define GDB_EXC_EMULATION      148 /* Emulation instruction */
#define GDB_EXC_SOFTWARE       149 /* Software generated exception */
#define GDB_EXC_BREAKPOINT     150 /* Breakpoint */



static unsigned char exception_to_signal[] = {
	[0]  = GDB_SIGFPE,  /* divide by zero */
	[1]  = GDB_SIGTRAP, /* debug exception */
	[2]  = GDB_SIGSEGV, /* NMI Interrupt */
	[3]  = GDB_SIGTRAP, /* Breakpoint */
	[4]  = GDB_SIGSEGV, /* into instruction (overflow) */
	[5]  = GDB_SIGSEGV, /* bound instruction */
	[6]  = GDB_SIGILL,  /* Invalid opcode */
	[7]  = GDB_SIGSEGV, /* coprocessor not available */
	[8]  = GDB_SIGSEGV, /* double fault */
	[9]  = GDB_SIGFPE,  /* coprocessor segment overrun */
	[10] = GDB_SIGSEGV, /* Invalid TSS */
	[11] = GDB_SIGBUS,  /* Segment not present */
	[12] = GDB_SIGBUS,  /* stack exception */
	[13] = GDB_SIGSEGV, /* general protection */
	[14] = GDB_SIGSEGV, /* page fault */
	[15] = GDB_UNKNOWN, /* reserved */
	[16] = GDB_SIGEMT,  /* coprocessor error */
	[17] = GDB_SIGBUS,  /* alignment check */
	[18] = GDB_SIGSEGV, /* machine check */
	[19] = GDB_SIGFPE,  /* simd floating point exception */
	[20] = GDB_UNKNOWN,
	[21] = GDB_UNKNOWN,
	[22] = GDB_UNKNOWN,
	[23] = GDB_UNKNOWN,
	[24] = GDB_UNKNOWN,
	[25] = GDB_UNKNOWN,
	[26] = GDB_UNKNOWN,
	[27] = GDB_UNKNOWN,
	[28] = GDB_UNKNOWN,
	[29] = GDB_UNKNOWN,
	[30] = GDB_UNKNOWN,
	[31] = GDB_UNKNOWN,
	[32] = GDB_SIGINT,  /* User interrupt */
};

static const char hexchars[] = "0123456789abcdef";
static char in_buffer[BUFMAX];
static char out_buffer[BUFMAX];


static inline void stub_putc(int ch)
{
	gdb_tx_byte(ch);
}

static inline void stub_flush(void)
{
	gdb_tx_flush();
}

static inline int stub_getc(void)
{
	return gdb_rx_byte();
}

static int hex(char ch)
{
	if ((ch >= 'a') && (ch <= 'f'))
		return (ch - 'a' + 10);
	if ((ch >= '0') && (ch <= '9'))
		return (ch - '0');
	if ((ch >= 'A') && (ch <= 'F'))
		return (ch - 'A' + 10);
	return (-1);
}

/*
 * While we find hexadecimal digits, build an int.
 * Fals is returned if nothing is parsed true otherwise.
 */
static int parse_ulong(char **ptr, unsigned long *value)
{
	int digit;
	char *start;

	start = *ptr;
	*value = 0;

	while ((digit = hex(**ptr)) >= 0) {
		*value = ((*value) << 4) | digit;
		(*ptr)++;
	}
	return start != *ptr;
}

/* convert the memory pointed to by mem into hex, placing result in buf */
/* return a pointer to the last char put in buf (null) */
static void copy_to_hex(char *buf, void *addr, unsigned long count)
{
	unsigned char ch;
	char *mem = addr;

	while (count--) {
		ch = *mem++;
		*buf++ = hexchars[ch >> 4];
		*buf++ = hexchars[ch & 0x0f];
	}
	*buf = 0;
}


/* convert the hex array pointed to by buf into binary to be placed in mem */
/* return a pointer to the character AFTER the last byte written */
static void copy_from_hex(void *addr, char *buf, unsigned long count)
{
	unsigned char ch;
	char *mem = addr;

	while (count--) {
		ch = hex(*buf++) << 4;
		ch = ch + hex(*buf++);
		*mem++ = ch;
	}
}


/* scan for the sequence $<data>#<checksum>	*/

static int get_packet(char *buffer)
{
	unsigned char checksum;
	unsigned char xmitcsum;
	int count;
	char ch;

	/* Wishlit implement a timeout in get_packet */
	do {
		/* wait around for the start character, ignore all other
		 * characters
		 */
		while ((ch = (stub_getc() & 0x7f)) != '$')
			;
		checksum = 0;
		xmitcsum = -1;

		count = 0;

		/* now, read until a # or end of buffer is found */
		while (count < BUFMAX) {
			ch = stub_getc() & 0x7f;
			if (ch == '#')
				break;
			checksum = checksum + ch;
			buffer[count] = ch;
			count = count + 1;
		}
		buffer[count] = 0;

		if (ch == '#') {
			xmitcsum = hex(stub_getc() & 0x7f) << 4;
			xmitcsum += hex(stub_getc() & 0x7f);

			if (checksum != xmitcsum) {
				stub_putc('-');	/* failed checksum */
				stub_flush();
			} else {
				stub_putc('+');	/* successful transfer */
				stub_flush();
			}
		}
	} while (checksum != xmitcsum);
	return 1;
}

/* send the packet in buffer.*/
static void put_packet(char *buffer)
{
	unsigned char checksum;
	int count;
	char ch;

	/*  $<packet info>#<checksum>. */
	do {
		stub_putc('$');
		checksum = 0;
		count = 0;

		while ((ch = buffer[count])) {
			stub_putc(ch);
			checksum += ch;
			count += 1;
		}

		stub_putc('#');
		stub_putc(hexchars[checksum >> 4]);
		stub_putc(hexchars[checksum % 16]);
		stub_flush();

	} while ((stub_getc() & 0x7f) != '+');

}
#endif /* CONFIG_GDB_STUB */

#include <arch/registers.h>

void x86_exception(struct eregs *info);

void x86_exception(struct eregs *info)
{
#if IS_ENABLED(CONFIG_GDB_STUB)
	int signo;
	memcpy(gdb_stub_registers, info, 8*sizeof(uint32_t));
	gdb_stub_registers[PC] = info->eip;
	gdb_stub_registers[CS] = info->cs;
	gdb_stub_registers[PS] = info->eflags;
	signo = GDB_UNKNOWN;
	if (info->vector < ARRAY_SIZE(exception_to_signal))
		signo = exception_to_signal[info->vector];

	/* reply to the host that an exception has occurred */
	out_buffer[0] = 'S';
	out_buffer[1] = hexchars[(signo>>4) & 0xf];
	out_buffer[2] = hexchars[signo & 0xf];
	out_buffer[3] = '\0';
	put_packet(out_buffer);

	while (1) {
		unsigned long addr, length;
		char *ptr;
		out_buffer[0] = '\0';
		out_buffer[1] = '\0';
		if (!get_packet(in_buffer))
			break;
		switch (in_buffer[0]) {
		case '?': /* last signal */
			out_buffer[0] = 'S';
			out_buffer[1] = hexchars[(signo >> 4) & 0xf];
			out_buffer[2] = hexchars[signo & 0xf];
			out_buffer[3] = '\0';
			break;
		case 'g': /* return the value of the CPU registers */
			copy_to_hex(out_buffer, &gdb_stub_registers,
				sizeof(gdb_stub_registers));
			break;
		case 'G': /* set the value of the CPU registers - return OK */
			copy_from_hex(&gdb_stub_registers, in_buffer + 1,
				sizeof(gdb_stub_registers));
			memcpy(info, gdb_stub_registers, 8*sizeof(uint32_t));
			info->eip    = gdb_stub_registers[PC];
			info->cs     = gdb_stub_registers[CS];
			info->eflags = gdb_stub_registers[PS];
			memcpy(out_buffer, "OK", 3);
			break;
		case 'm':
			/* mAA..AA,LLLL  Read LLLL bytes at address AA..AA */
			ptr = &in_buffer[1];
			if (parse_ulong(&ptr, &addr) &&
				(*ptr++ == ',') &&
				parse_ulong(&ptr, &length)) {
				copy_to_hex(out_buffer, (void *)addr, length);
			} else
				memcpy(out_buffer, "E01", 4);
			break;
		case 'M':
			/* MAA..AA,LLLL: Write LLLL bytes at address AA.AA
			 * return OK
			 */
			ptr = &in_buffer[1];
			if (parse_ulong(&ptr, &addr) &&
				(*(ptr++) == ',') &&
				parse_ulong(&ptr, &length) &&
				(*(ptr++) == ':')) {
				copy_from_hex((void *)addr, ptr, length);
				memcpy(out_buffer, "OK", 3);
			} else
				memcpy(out_buffer, "E02", 4);
			break;
		case 's':
		case 'c':
			/* cAA..AA    Continue at address AA..AA(optional)
			 * sAA..AA    Step one instruction from AA..AA(optional)
			 */
			ptr = &in_buffer[1];
			if (parse_ulong(&ptr, &addr))
				info->eip = addr;

			/* Clear the trace bit */
			info->eflags &= ~(1 << 8);
			/* Set the trace bit if we are single stepping */
			if (in_buffer[0] == 's')
				info->eflags |= (1 << 8);
			return;
		case 'D':
			memcpy(out_buffer, "OK", 3);
			break;
		case 'k':  /* kill request? */
			break;
		case 'q':  /* query */
			break;
		case 'z':  /* z0AAAA,LLLL remove memory breakpoint */
			   /* z1AAAA,LLLL remove hardware breakpoint */
			   /* z2AAAA,LLLL remove write watchpoint */
			   /* z3AAAA,LLLL remove read watchpoint */
			   /* z4AAAA,LLLL remove access watchpoint */
		case 'Z':  /* Z0AAAA,LLLL insert memory breakpoint */
			   /* Z1AAAA,LLLL insert hardware breakpoint */
			   /* Z2AAAA,LLLL insert write watchpoint */
			   /* Z3AAAA,LLLL insert read watchpoint */
			   /* Z4AAAA,LLLL insert access watchpoint */
			break;
		default:
			break;
		}
		put_packet(out_buffer);
	}
#else /* !CONFIG_GDB_STUB */
#define MDUMP_SIZE 0x80
	unsigned int logical_processor = 0;

#if ENV_RAMSTAGE
	logical_processor = cpu_index();
#endif
	printk(BIOS_EMERG,
		"CPU Index %d - APIC %d Unexpected Exception:"
		"%d @ %02x:%08x - Halting\n"
		"Code: %d eflags: %08x cr2: %08x\n"
		"eax: %08x ebx: %08x ecx: %08x edx: %08x\n"
		"edi: %08x esi: %08x ebp: %08x esp: %08x\n",
		logical_processor, (unsigned int)lapicid(),
		info->vector, info->cs, info->eip,
		info->error_code, info->eflags, read_cr2(),
		info->eax, info->ebx, info->ecx, info->edx,
		info->edi, info->esi, info->ebp, info->esp);
	u8 *code = (u8 *)((uintptr_t)info->eip - (MDUMP_SIZE >> 1));
	/* Align to 8-byte boundary please, and print eight bytes per row.
	 * This is done to make DRAM burst timing/reordering errors more
	 * evident from the looking at the dump */
	code = (u8 *)((uintptr_t)code & ~0x7);
	int i;
	for (i = 0; i < MDUMP_SIZE; i++) {
		if ((i & 0x07) == 0)
			printk(BIOS_EMERG, "\n%p:\t", code + i);
		printk(BIOS_EMERG, "%.2x ", code[i]);
	}
	die("");
#endif
}

#define GATE_P		(1 << 15)
#define GATE_DPL(x)	(((x) & 0x3) << 13)
#define GATE_SIZE_16	(0 << 11)
#define GATE_SIZE_32	(1 << 11)

#define IGATE_FLAGS (GATE_P | GATE_DPL(0) | GATE_SIZE_32 | (0x6 << 8))

struct intr_gate {
	uint16_t offset_0;
	uint16_t segsel;
	uint16_t flags;
	uint16_t offset_1;
#if ENV_X86_64
	uint32_t offset_2;
	uint32_t reserved;
#endif
} __packed;

/* Even though the vecX symbols are interrupt entry points just treat them
   like data to more easily get the pointer values in C. Because IDT entries
   format splits the offset field up, one can't use the linker to resolve
   parts of a relocation on x86 ABI. An array of pointers is used to gather
   the symbols. The IDT is initialized at runtime when exception_init() is
   called. */
extern u8 vec0[], vec1[], vec2[], vec3[], vec4[], vec5[], vec6[], vec7[];
extern u8 vec8[], vec9[], vec10[], vec11[], vec12[], vec13[], vec14[], vec15[];
extern u8 vec16[], vec17[], vec18[], vec19[];

static const uintptr_t intr_entries[] = {
	(uintptr_t)vec0, (uintptr_t)vec1, (uintptr_t)vec2, (uintptr_t)vec3,
	(uintptr_t)vec4, (uintptr_t)vec5, (uintptr_t)vec6, (uintptr_t)vec7,
	(uintptr_t)vec8, (uintptr_t)vec9, (uintptr_t)vec10, (uintptr_t)vec11,
	(uintptr_t)vec12, (uintptr_t)vec13, (uintptr_t)vec14, (uintptr_t)vec15,
	(uintptr_t)vec16, (uintptr_t)vec17, (uintptr_t)vec18, (uintptr_t)vec19,
};

static struct intr_gate idt[ARRAY_SIZE(intr_entries)] __aligned(8) CAR_GLOBAL;

static inline uint16_t get_cs(void)
{
	uint16_t segment;

	asm volatile (
		"mov	%%cs, %0\n"
		: "=r" (segment)
		:
		: "memory"
	);

	return segment;
}

struct lidtarg {
	uint16_t limit;
#if ENV_X86_32
	uint32_t base;
#else
	uint64_t base;
#endif
} __packed;

/* This global is for src/cpu/x86/lapic/secondary.S usage which is only
   used during ramstage. */
struct lidtarg idtarg;

static void load_idt(void *table, size_t sz)
{
	struct lidtarg lidtarg = {
		.limit = sz - 1,
		.base = (uintptr_t)table,
	};

	asm volatile (
		"lidt	%0"
		:
		: "m" (lidtarg)
		: "memory"
	);

	if (ENV_RAMSTAGE)
		memcpy(&idtarg, &lidtarg, sizeof(idtarg));
}

asmlinkage void exception_init(void)
{
	int i;
	uint16_t segment;
	struct intr_gate *gates;

	segment = get_cs();
	gates = car_get_var_ptr(idt);

	/* Initialize IDT. */
	for (i = 0; i < ARRAY_SIZE(idt); i++) {
		gates[i].offset_0 = intr_entries[i];
		gates[i].segsel = segment;
		gates[i].flags = IGATE_FLAGS;
		gates[i].offset_1 = intr_entries[i] >> 16;
#if ENV_X86_64
		gates[i].offset_2 = intr_entries[i] >> 32;
#endif
	}

	load_idt(gates, sizeof(idt));
}