kgdb.c

Kernel code of linux kernel

/*
 * KGDB stub.
 *
 * Maintainer: Jason Wessel <[e-mail]>
 *
 * Copyright (C) 2000-2001 VERITAS Software Corporation.
 * Copyright (C) 2002-2004 Timesys Corporation
 * Copyright (C) 2003-2004 Amit S. Kale <[e-mail]>
 * Copyright (C) 2004 Pavel Machek <[e-mail]>
 * Copyright (C) 2004-2006 Tom Rini <[e-mail]>
 * Copyright (C) 2004-2006 LinSysSoft Technologies Pvt. Ltd.
 * Copyright (C) 2005-2008 Wind River Systems, Inc.
 * Copyright (C) 2007 MontaVista Software, Inc.
 * Copyright (C) 2008 Red Hat, Inc., Ingo Molnar <[e-mail]>
 *
 * Contributors at various stages not listed above:
 *  Jason Wessel ( [e-mail] )
 *  George Anzinger <[e-mail]>
 *  Anurekh Saxena ([e-mail])
 *  Lake Stevens Instrument Division (Glenn Engel)
 *  Jim Kingdon, Cygnus Support.
 *
 * Original KGDB stub: David Grothe <[e-mail]>,
 * Tigran Aivazian <[e-mail]>
 *
 * This file is licensed under the terms of the GNU General Public License
 * version 2. This program is licensed "as is" without any warranty of any
 * kind, whether express or implied.
 */
#include <linux/pid_namespace.h>
#include <linux/clocksource.h>
#include <linux/interrupt.h>
#include <linux/spinlock.h>
#include <linux/console.h>
#include <linux/threads.h>
#include <linux/uaccess.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/ptrace.h>
#include <linux/reboot.h>
#include <linux/string.h>
#include <linux/delay.h>
#include <linux/sched.h>
#include <linux/sysrq.h>
#include <linux/init.h>
#include <linux/kgdb.h>
#include <linux/pid.h>
#include <linux/smp.h>
#include <linux/mm.h>

#include <asm/cacheflush.h>
#include <asm/byteorder.h>
#include <asm/atomic.h>
#include <asm/system.h>
#include <asm/unaligned.h>

static int kgdb_break_asap;

#define KGDB_MAX_THREAD_QUERY 17
struct kgdb_state {
	int			ex_vector;
	int			signo;
	int			err_code;
	int			cpu;
	int			pass_exception;
	unsigned long		thr_query;
	unsigned long		threadid;
	long			kgdb_usethreadid;
	struct pt_regs		*linux_regs;
};

static struct debuggerinfo_struct {
	void			*debuggerinfo;
	struct task_struct	*task;
} kgdb_info[NR_CPUS];

/**
 * kgdb_connected - Is a host GDB connected to us?
 */
int				kgdb_connected;
EXPORT_SYMBOL_GPL(kgdb_connected);

/* All the KGDB handlers are installed */
static int			kgdb_io_module_registered;

/* Guard for recursive entry */
static int			exception_level;

static struct kgdb_io		*kgdb_io_ops;
static DEFINE_SPINLOCK(kgdb_registration_lock);

/* kgdb console driver is loaded */
static int kgdb_con_registered;
/* determine if kgdb console output should be used */
static int kgdb_use_con;

static int __init opt_kgdb_con(char *str)
{
	kgdb_use_con = 1;
	return 0;
}

early_param("kgdbcon", opt_kgdb_con);

module_param(kgdb_use_con, int, 0644);

/*
 * Holds information about breakpoints in a kernel. These breakpoints are
 * added and removed by gdb.
 */
static struct kgdb_bkpt		kgdb_break[KGDB_MAX_BREAKPOINTS] = {
	[0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
};

/*
 * The CPU# of the active CPU, or -1 if none:
 */
atomic_t			kgdb_active = ATOMIC_INIT(-1);

/*
 * We use NR_CPUs not PERCPU, in case kgdb is used to debug early
 * bootup code (which might not have percpu set up yet):
 */
static atomic_t			passive_cpu_wait[NR_CPUS];
static atomic_t			cpu_in_kgdb[NR_CPUS];
atomic_t			kgdb_setting_breakpoint;

struct task_struct		*kgdb_usethread;
struct task_struct		*kgdb_contthread;

int				kgdb_single_step;

/* Our I/O buffers. */
static char			remcom_in_buffer[BUFMAX];
static char			remcom_out_buffer[BUFMAX];

/* Storage for the registers, in GDB format. */
static unsigned long		gdb_regs[(NUMREGBYTES +
					sizeof(unsigned long) - 1) /
					sizeof(unsigned long)];

/* to keep track of the CPU which is doing the single stepping*/
atomic_t			kgdb_cpu_doing_single_step = ATOMIC_INIT(-1);

/*
 * If you are debugging a problem where roundup (the collection of
 * all other CPUs) is a problem [this should be extremely rare],
 * then use the nokgdbroundup option to avoid roundup. In that case
 * the other CPUs might interfere with your debugging context, so
 * use this with care:
 */
static int kgdb_do_roundup = 1;

static int __init opt_nokgdbroundup(char *str)
{
	kgdb_do_roundup = 0;

	return 0;
}

early_param("nokgdbroundup", opt_nokgdbroundup);

/*
 * Finally, some KGDB code :-)
 */

/*
 * Weak aliases for breakpoint management,
 * can be overriden by architectures when needed:
 */
int __weak kgdb_arch_set_breakpoint(unsigned long addr, char *saved_instr)
{
	int err;

	err = probe_kernel_read(saved_instr, (char *)addr, BREAK_INSTR_SIZE);
	if (err)
		return err;

	return probe_kernel_write((char *)addr, arch_kgdb_ops.gdb_bpt_instr,
				  BREAK_INSTR_SIZE);
}

int __weak kgdb_arch_remove_breakpoint(unsigned long addr, char *bundle)
{
	return probe_kernel_write((char *)addr,
				  (char *)bundle, BREAK_INSTR_SIZE);
}

int __weak kgdb_validate_break_address(unsigned long addr)
{
	char tmp_variable[BREAK_INSTR_SIZE];
	int err;
	/* Validate setting the breakpoint and then removing it.  In the
	 * remove fails, the kernel needs to emit a bad message because we
	 * are deep trouble not being able to put things back the way we
	 * found them.
	 */
	err = kgdb_arch_set_breakpoint(addr, tmp_variable);
	if (err)
		return err;
	err = kgdb_arch_remove_breakpoint(addr, tmp_variable);
	if (err)
		printk(KERN_ERR "KGDB: Critical breakpoint error, kernel "
		   "memory destroyed at: %lx", addr);
	return err;
}

unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
{
	return instruction_pointer(regs);
}

int __weak kgdb_arch_init(void)
{
	return 0;
}

int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
{
	return 0;
}

void __weak
kgdb_post_primary_code(struct pt_regs *regs, int e_vector, int err_code)
{
	return;
}

/**
 *	kgdb_disable_hw_debug - Disable hardware debugging while we in kgdb.
 *	@regs: Current &struct pt_regs.
 *
 *	This function will be called if the particular architecture must
 *	disable hardware debugging while it is processing gdb packets or
 *	handling exception.
 */
void __weak kgdb_disable_hw_debug(struct pt_regs *regs)
{
}

/*
 * GDB remote protocol parser:
 */

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;
}

/* scan for the sequence $<data>#<checksum> */
static void get_packet(char *buffer)
{
	unsigned char checksum;
	unsigned char xmitcsum;
	int count;
	char ch;

	do {
		/*
		 * Spin and wait around for the start character, ignore all
		 * other characters:
		 */
		while ((ch = (kgdb_io_ops->read_char())) != '$')
			/* nothing */;

		kgdb_connected = 1;
		checksum = 0;
		xmitcsum = -1;

		count = 0;

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

		if (ch == '#') {
			xmitcsum = hex(kgdb_io_ops->read_char()) << 4;
			xmitcsum += hex(kgdb_io_ops->read_char());

			if (checksum != xmitcsum)
				/* failed checksum */
				kgdb_io_ops->write_char('-');
			else
				/* successful transfer */
				kgdb_io_ops->write_char('+');
			if (kgdb_io_ops->flush)
				kgdb_io_ops->flush();
		}
	} while (checksum != xmitcsum);
}

/*
 * Send the packet in buffer.
 * Check for gdb connection if asked for.
 */
static void put_packet(char *buffer)
{
	unsigned char checksum;
	int count;
	char ch;

	/*
	 * $<packet info>#<checksum>.
	 */
	while (1) {
		kgdb_io_ops->write_char('$');
		checksum = 0;
		count = 0;

		while ((ch = buffer[count])) {
			kgdb_io_ops->write_char(ch);
			checksum += ch;
			count++;
		}

		kgdb_io_ops->write_char('#');
		kgdb_io_ops->write_char(hex_asc_hi(checksum));
		kgdb_io_ops->write_char(hex_asc_lo(checksum));
		if (kgdb_io_ops->flush)
			kgdb_io_ops->flush();

		/* Now see what we get in reply. */
		ch = kgdb_io_ops->read_char();

		if (ch == 3)
			ch = kgdb_io_ops->read_char();

		/* If we get an ACK, we are done. */
		if (ch == '+')
			return;

		/*
		 * If we get the start of another packet, this means
		 * that GDB is attempting to reconnect.  We will NAK
		 * the packet being sent, and stop trying to send this
		 * packet.
		 */
		if (ch == '$') {
			kgdb_io_ops->write_char('-');
			if (kgdb_io_ops->flush)
				kgdb_io_ops->flush();
			return;
		}
	}
}

/*
 * Convert the memory pointed to by mem into hex, placing result in buf.
 * Return a pointer to the last char put in buf (null). May return an error.
 */
int kgdb_mem2hex(char *mem, char *buf, int count)
{
	char *tmp;
	int err;

	/*
	 * We use the upper half of buf as an intermediate buffer for the
	 * raw memory copy.  Hex conversion will work against this one.
	 */
	tmp = buf + count;

	err = probe_kernel_read(tmp, mem, count);
	if (!err) {
		while (count > 0) {
			buf = pack_hex_byte(buf, *tmp);
			tmp++;
			count--;
		}

		*buf = 0;
	}

	return err;
}

/*
 * Copy the binary array pointed to by buf into mem.  Fix $, #, and
 * 0x7d escaped with 0x7d.  Return a pointer to the character after
 * the last byte written.
 */
static int kgdb_ebin2mem(char *buf, char *mem, int count)
{
	int err = 0;
	char c;

	while (count-- > 0) {
		c = *buf++;
		if (c == 0x7d)
			c = *buf++ ^ 0x20;

		err = probe_kernel_write(mem, &c, 1);
		if (err)
			break;

		mem++;
	}

	return err;
}

/*
 * 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.
 * May return an error.
 */
int kgdb_hex2mem(char *buf, char *mem, int count)
{
	char *tmp_raw;
	char *tmp_hex;

	/*
	 * We use the upper half of buf as an intermediate buffer for the
	 * raw memory that is converted from hex.
	 */
	tmp_raw = buf + count * 2;

	tmp_hex = tmp_raw - 1;
	while (tmp_hex >= buf) {
		tmp_raw--;
		*tmp_raw = hex(*tmp_hex--);
		*tmp_raw |= hex(*tmp_hex--) << 4;
	}

	return probe_kernel_write(mem, tmp_raw, count);
}

/*
 * While we find nice hex chars, build a long_val.
 * Return number of chars processed.
 */
int kgdb_hex2long(char **ptr, unsigned long *long_val)
{
	int hex_val;
	int num = 0;
	int negate = 0;

	*long_val = 0;

	if (**ptr == '-') {
		negate = 1;
		(*ptr)++;
	}
	while (**ptr) {
		hex_val = hex(**ptr);
		if (hex_val < 0)
			break;

		*long_val = (*long_val << 4) | hex_val;
		num++;
		(*ptr)++;
	}

	if (negate)
		*long_val = -*long_val;

	return num;
}

/* Write memory due to an 'M' or 'X' packet. */
static int write_mem_msg(int binary)
{
	char *ptr = &remcom_in_buffer[1];
	unsigned long addr;
	unsigned long length;
	int err;

	if (kgdb_hex2long(&ptr, &addr) > 0 && *(ptr++) == ',' &&
	    kgdb_hex2long(&ptr, &length) > 0 && *(ptr++) == ':') {
		if (binary)
			err = kgdb_ebin2mem(ptr, (char *)addr, length);
		else
			err = kgdb_hex2mem(ptr, (char *)addr, length);
		if (err)
			return err;
		if (CACHE_FLUSH_IS_SAFE)
			flush_icache_range(addr, addr + length);
		return 0;
	}

	return -EINVAL;
}

static void error_packet(char *pkt, int error)
{
	error = -error;
	pkt[0] = 'E';
	pkt[1] = hex_asc[(error / 10)];
	pkt[2] = hex_asc[(error % 10)];
	pkt[3] = '\0';
}

/*
 * Thread ID accessors. We represent a flat TID space to GDB, where
 * the per CPU idle threads (which under Linux all have PID 0) are
 * remapped to negative TIDs.
 */

#define BUF_THREAD_ID_SIZE	16

static char *pack_threadid(char *pkt, unsigned char *id)
{
	char *limit;

	limit = pkt + BUF_THREAD_ID_SIZE;
	while (pkt < limit)
		pkt = pack_hex_byte(pkt, *id++);

	return pkt;
}

static void int_to_threadref(unsigned char *id, int value)
{
	unsigned char *scan;
	int i = 4;

	scan = (unsigned char *)id;
	while (i--)
		*scan++ = 0;
	put_unaligned_be32(value, scan);
}

static struct task_struct *getthread(struct pt_regs *regs, int tid)
{
	/*
	 * Non-positive TIDs are remapped to the cpu shadow information
	 */
	if (tid == 0 || tid == -1)
		tid = -atomic_read(&kgdb_active) - 2;
	if (tid < 0) {
		if (kgdb_info[-tid - 2].task)
			return kgdb_info[-tid - 2].task;
		else
			return idle_task(-tid - 2);
	}

	/*
	 * find_task_by_pid_ns() does not take the tasklist lock anymore
	 * but is nicely RCU locked - hence is a pretty resilient
	 * thing to use:
	 */
	return find_task_by_pid_ns(tid, &init_pid_ns);
}

/*
 * CPU debug state control:
 */

#ifdef CONFIG_SMP
static void kgdb_wait(struct pt_regs *regs)
{
	unsigned long flags;
	int cpu;

	local_irq_save(flags);
	cpu = raw_smp_processor_id();
	kgdb_info[cpu].debuggerinfo = regs;
	kgdb_info[cpu].task = current;
	/*
	 * Make sure the above info reaches the primary CPU before
	 * our cpu_in_kgdb[] flag setting does:
	 */
	smp_wmb();
	atomic_set(&cpu_in_kgdb[cpu], 1);