Release 4.15 kernel/debug/gdbstub.c

/*
 * Kernel Debug Core
 *
 * Maintainer: Jason Wessel <jason.wessel@windriver.com>
 *
 * Copyright (C) 2000-2001 VERITAS Software Corporation.
 * Copyright (C) 2002-2004 Timesys Corporation
 * Copyright (C) 2003-2004 Amit S. Kale <amitkale@linsyssoft.com>
 * Copyright (C) 2004 Pavel Machek <pavel@ucw.cz>
 * Copyright (C) 2004-2006 Tom Rini <trini@kernel.crashing.org>
 * Copyright (C) 2004-2006 LinSysSoft Technologies Pvt. Ltd.
 * Copyright (C) 2005-2009 Wind River Systems, Inc.
 * Copyright (C) 2007 MontaVista Software, Inc.
 * Copyright (C) 2008 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 *
 * Contributors at various stages not listed above:
 *  Jason Wessel ( jason.wessel@windriver.com )
 *  George Anzinger <george@mvista.com>
 *  Anurekh Saxena (anurekh.saxena@timesys.com)
 *  Lake Stevens Instrument Division (Glenn Engel)
 *  Jim Kingdon, Cygnus Support.
 *
 * Original KGDB stub: David Grothe <dave@gcom.com>,
 * Tigran Aivazian <tigran@sco.com>
 *
 * 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/kernel.h>
#include <linux/sched/signal.h>
#include <linux/kgdb.h>
#include <linux/kdb.h>
#include <linux/serial_core.h>
#include <linux/reboot.h>
#include <linux/uaccess.h>
#include <asm/cacheflush.h>
#include <asm/unaligned.h>
#include "debug_core.h"


#define KGDB_MAX_THREAD_QUERY 17

/* Our I/O buffers. */

static char			remcom_in_buffer[BUFMAX];

static char			remcom_out_buffer[BUFMAX];

static int			gdbstub_use_prev_in_buf;

static int			gdbstub_prev_in_buf_pos;

/* Storage for the registers, in GDB format. */

static unsigned long		gdb_regs[(NUMREGBYTES +
					sizeof(unsigned long) - 1) /
					sizeof(unsigned long)];

/*
 * GDB remote protocol parser:
 */

#ifdef CONFIG_KGDB_KDB


static int gdbstub_read_wait(void)
{
	int ret = -1;
	int i;

	if (unlikely(gdbstub_use_prev_in_buf)) {
		if (gdbstub_prev_in_buf_pos < gdbstub_use_prev_in_buf)
			return remcom_in_buffer[gdbstub_prev_in_buf_pos++];
		else
			gdbstub_use_prev_in_buf = 0;
	}

	/* poll any additional I/O interfaces that are defined */
	while (ret < 0)
		for (i = 0; kdb_poll_funcs[i] != NULL; i++) {
			ret = kdb_poll_funcs[i]();
			if (ret > 0)
				break;
		}
	return ret;
}
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#else


static int gdbstub_read_wait(void)
{
	int ret = dbg_io_ops->read_char();
	while (ret == NO_POLL_CHAR)
		ret = dbg_io_ops->read_char();
	return ret;
}
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#endif
/* 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 = (gdbstub_read_wait())) != '$')
			/* 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 = gdbstub_read_wait();
			if (ch == '#')
				break;
			checksum = checksum + ch;
			buffer[count] = ch;
			count = count + 1;
		}

		if (ch == '#') {
			xmitcsum = hex_to_bin(gdbstub_read_wait()) << 4;
			xmitcsum += hex_to_bin(gdbstub_read_wait());

			if (checksum != xmitcsum)
				/* failed checksum */
				dbg_io_ops->write_char('-');
			else
				/* successful transfer */
				dbg_io_ops->write_char('+');
			if (dbg_io_ops->flush)
				dbg_io_ops->flush();
		}
		buffer[count] = 0;
	} while (checksum != xmitcsum);
}

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/*
 * 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;

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

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

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

		/* Now see what we get in reply. */
		ch = gdbstub_read_wait();

		if (ch == 3)
			ch = gdbstub_read_wait();

		/* 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 == '$') {
			dbg_io_ops->write_char('-');
			if (dbg_io_ops->flush)
				dbg_io_ops->flush();
			return;
		}
	}
}

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static char gdbmsgbuf[BUFMAX + 1];



void gdbstub_msg_write(const char *s, int len)
{
	char *bufptr;
	int wcount;
	int i;

	if (len == 0)
		len = strlen(s);

	/* 'O'utput */
	gdbmsgbuf[0] = 'O';

	/* Fill and send buffers... */
	while (len > 0) {
		bufptr = gdbmsgbuf + 1;

		/* Calculate how many this time */
		if ((len << 1) > (BUFMAX - 2))
			wcount = (BUFMAX - 2) >> 1;
		else
			wcount = len;

		/* Pack in hex chars */
		for (i = 0; i < wcount; i++)
			bufptr = hex_byte_pack(bufptr, s[i]);
		*bufptr = '\0';

		/* Move up */
		s += wcount;
		len -= wcount;

		/* Write packet */
		put_packet(gdbmsgbuf);
	}
}

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/*
 * 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.
 */


char *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)
		return NULL;
	while (count > 0) {
		buf = hex_byte_pack(buf, *tmp);
		tmp++;
		count--;
	}
	*buf = 0;

	return buf;
}

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/*
 * 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_to_bin(*tmp_hex--);
		*tmp_raw |= hex_to_bin(*tmp_hex--) << 4;
	}

	return probe_kernel_write(mem, tmp_raw, count);
}

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/*
 * 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_to_bin(**ptr);
		if (hex_val < 0)
			break;

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

	if (negate)
		*long_val = -*long_val;

	return num;
}

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/*
 * Copy the binary array pointed to by buf into mem.  Fix $, #, and
 * 0x7d escaped with 0x7d. Return -EFAULT on failure or 0 on success.
 * The input buf is overwitten with the result to write to mem.
 */


static int kgdb_ebin2mem(char *buf, char *mem, int count)
{
	int size = 0;
	char *c = buf;

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

	return probe_kernel_write(mem, c, size);
}

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#if DBG_MAX_REG_NUM > 0


void pt_regs_to_gdb_regs(unsigned long *gdb_regs, struct pt_regs *regs)
{
	int i;
	int idx = 0;
	char *ptr = (char *)gdb_regs;

	for (i = 0; i < DBG_MAX_REG_NUM; i++) {
		dbg_get_reg(i, ptr + idx, regs);
		idx += dbg_reg_def[i].size;
	}
}

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void gdb_regs_to_pt_regs(unsigned long *gdb_regs, struct pt_regs *regs)
{
	int i;
	int idx = 0;
	char *ptr = (char *)gdb_regs;

	for (i = 0; i < DBG_MAX_REG_NUM; i++) {
		dbg_set_reg(i, ptr + idx, regs);
		idx += dbg_reg_def[i].size;
	}
}
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#endif /* DBG_MAX_REG_NUM > 0 */

/* 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;
}

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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';
}

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/*
 * 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	8



static char *pack_threadid(char *pkt, unsigned char *id)
{
	unsigned char *limit;
	int lzero = 1;

	limit = id + (BUF_THREAD_ID_SIZE / 2);
	while (id < limit) {
		if (!lzero || *id != 0) {
			pkt = hex_byte_pack(pkt, *id);
			lzero = 0;
		}
		id++;
	}

	if (lzero)
		pkt = hex_byte_pack(pkt, 0);

	return pkt;
}

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static void int_to_threadref(unsigned char *id, int value)
{
	put_unaligned_be32(value, id);
}

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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 < -1 && tid > -NR_CPUS - 2) {
		if (kgdb_info[-tid - 2].task)
			return kgdb_info[-tid - 2].task;
		else
			return idle_task(-tid - 2);
	}
	if (tid <= 0) {
		printk(KERN_ERR "KGDB: Internal thread select error\n");
		dump_stack();
		return NULL;
	}

	/*
         * 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);
}


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/*
 * Remap normal tasks to their real PID,
 * CPU shadow threads are mapped to -CPU - 2
 */


static inline int shadow_pid(int realpid)
{
	if (realpid)
		return realpid;

	return -raw_smp_processor_id() - 2;
}

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/*
 * All the functions that start with gdb_cmd are the various
 * operations to implement the handlers for the gdbserial protocol
 * where KGDB is communicating with an external debugger
 */

/* Handle the '?' status packets */


static void gdb_cmd_status(struct kgdb_state *ks)
{
	/*
         * We know that this packet is only sent
         * during initial connect.  So to be safe,
         * we clear out our breakpoints now in case
         * GDB is reconnecting.
         */
	dbg_remove_all_break();

	remcom_out_buffer[0] = 'S';
	hex_byte_pack(&remcom_out_buffer[1], ks->signo);
}

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static void gdb_get_regs_helper(struct kgdb_state *ks)
{
	struct task_struct *thread;
	void *local_debuggerinfo;
	int i;

	thread = kgdb_usethread;
	if (!thread) {
		thread = kgdb_info[ks->cpu].task;
		local_debuggerinfo = kgdb_info[ks->cpu].debuggerinfo;
	} else {
		local_debuggerinfo = NULL;
		for_each_online_cpu(i) {
			/*
                         * Try to find the task on some other
                         * or possibly this node if we do not
                         * find the matching task then we try
                         * to approximate the results.
                         */
			if (thread == kgdb_info[i].task)
				local_debuggerinfo = kgdb_info[i].debuggerinfo;
		}
	}

	/*
         * All threads that don't have debuggerinfo should be
         * in schedule() sleeping, since all other CPUs
         * are in kgdb_wait, and thus have debuggerinfo.
         */
	if (local_debuggerinfo) {
		pt_regs_to_gdb_regs(gdb_regs, local_debuggerinfo);
	} else {
		/*
                 * Pull stuff saved during switch_to; nothing
                 * else is accessible (or even particularly
                 * relevant).
                 *
                 * This should be enough for a stack trace.
                 */
		sleeping_thread_to_gdb_regs(gdb_regs, thread);
	}
}

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/* Handle the 'g' get registers request */


static void gdb_cmd_getregs(struct kgdb_state *ks)
{
	gdb_get_regs_helper(ks);
	kgdb_mem2hex((char *)gdb_regs, remcom_out_buffer, NUMREGBYTES);
}

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/* Handle the 'G' set registers request */


static void gdb_cmd_setregs(struct kgdb_state *ks)
{
	kgdb_hex2mem(&remcom_in_buffer[1], (char *)gdb_regs, NUMREGBYTES);

	if (kgdb_usethread && kgdb_usethread != current) {
		error_packet(remcom_out_buffer, -EINVAL);
	} else {
		gdb_regs_to_pt_regs(gdb_regs, ks->linux_regs);
		strcpy(remcom_out_buffer, "OK");
	}
}

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/* Handle the 'm' memory read bytes */


static void gdb_cmd_memread(struct kgdb_state *ks)
{
	char *ptr = &remcom_in_buffer[1];
	unsigned long length;
	unsigned long addr;
	char *err;

	if (kgdb_hex2long(&ptr, &addr) > 0 && *ptr++ == ',' &&
					kgdb_hex2long(&ptr, &length) > 0) {
		err = kgdb_mem2hex((char *)addr, remcom_out_buffer, length);
		if (!err)
			error_packet(remcom_out_buffer, -EINVAL);
	} else {
		error_packet(remcom_out_buffer, -EINVAL);
	}
}

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/* Handle the 'M' memory write bytes */


static void gdb_cmd_memwrite(struct kgdb_state *ks)
{
	int err = write_mem_msg(0);

	if (err)
		error_packet(remcom_out_buffer, err);
	else
		strcpy(remcom_out_buffer, "OK");
}

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#if DBG_MAX_REG_NUM > 0


static char *gdb_hex_reg_helper(int regnum, char *out)
{
	int i;
	int offset = 0;

	for (i = 0; i < regnum; i++)
		offset += dbg_reg_def[i].size;
	return kgdb_mem2hex((char *)gdb_regs + offset, out,
			    dbg_reg_def[i].size);
}

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/* Handle the 'p' individual regster get */


static void gdb_cmd_reg_get(struct kgdb_state *ks)
{
	unsigned long regnum;
	char *ptr = &remcom_in_buffer[1];

	kgdb_hex2long(&ptr, &regnum);
	if (regnum >= DBG_MAX_REG_NUM) {
		error_packet(remcom_out_buffer, -EINVAL);
		return;
	}
	gdb_get_regs_helper(ks);
	gdb_hex_reg_helper(regnum, remcom_out_buffer);
}

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/* Handle the 'P' individual regster set */


static void gdb_cmd_reg_set(struct kgdb_state *ks)
{
	unsigned long regnum;
	char *ptr = &remcom_in_buffer[1];
	int i = 0;

	kgdb_hex2long(&ptr, &regnum);
	if (*ptr++ != '=' ||
	    !(!kgdb_usethread || kgdb_usethread == current) ||
	    !dbg_get_reg(regnum, gdb_regs, ks->linux_regs)) {
		error_packet(remcom_out_buffer, -EINVAL);
		return;
	}
	memset(gdb_regs, 0, sizeof(gdb_regs));
	while (i < sizeof(gdb_regs) * 2)
		if (hex_to_bin(ptr[i]) >= 0)
			i++;
		else
			break;
	i = i / 2;
	kgdb_hex2mem(ptr, (char *)gdb_regs, i);
	dbg_set_reg(regnum, gdb_regs, ks->linux_regs);
	strcpy(remcom_out_buffer, "OK");
}
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#endif /* DBG_MAX_REG_NUM > 0 */

/* Handle the 'X' memory binary write bytes */


static void gdb_cmd_binwrite(struct kgdb_state *ks)
{
	int err = write_mem_msg(1);

	if (err)
		error_packet(remcom_out_buffer, err);
	else
		strcpy(remcom_out_buffer, "OK");
}

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/* Handle the 'D' or 'k', detach or kill packets */


static void gdb_cmd_detachkill(struct kgdb_state *ks)
{
	int error;

	/* The detach case */
	if (remcom_in_buffer[0] == 'D') {
		error = dbg_remove_all_break();
		if (error < 0) {
			error_packet(remcom_out_buffer, error);
		} else {
			strcpy(remcom_out_buffer, "OK");
			kgdb_connected = 0;
		}
		put_packet(remcom_out_buffer);
	} else {
		/*
                 * Assume the kill case, with no exit code checking,
                 * trying to force detach the debugger:
                 */
		dbg_remove_all_break();
		kgdb_connected = 0;
	}
}

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/* Handle the 'R' reboot packets */


static int gdb_cmd_reboot(struct kgdb_state *ks)
{
	/* For now, only honor R0 */
	if (strcmp(remcom_in_buffer, "R0") == 0) {
		printk(KERN_CRIT "Executing emergency reboot\n");
		strcpy(remcom_out_buffer, "OK");
		put_packet(remcom_out_buffer);

		/*
                 * Execution should not return from
                 * machine_emergency_restart()
                 */
		machine_emergency_restart();
		kgdb_connected = 0;

		return 1;
	}
	return 0;
}

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/* Handle the 'q' query packets */


static void gdb_cmd_query(struct kgdb_state *ks)
{
	struct task_struct *g;
	struct task_struct *p;
	unsigned char thref[BUF_THREAD_ID_SIZE];
	char *ptr;
	int i;
	int cpu;
	int finished = 0;

	switch (remcom_in_buffer[1]) {
	case 's':
	case 'f':
		if (memcmp(remcom_in_buffer + 2, "ThreadInfo", 10))
			break;

		i = 0;
		remcom_out_buffer[0] = 'm';
		ptr = remcom_out_buffer + 1;
		if (remcom_in_buffer[1] == 'f') {
			/* Each cpu is a shadow thread */
			for_each_online_cpu(cpu) {
				ks->thr_query = 0;
				int_to_threadref(thref, -cpu - 2);
				ptr = pack_threadid(ptr, thref);
				*(ptr++) = ',';
				i++;
			}
		}

		do_each_thread(g, p) {
			if (i >= ks->thr_query && !finished) {
				int_to_threadref(thref, p->pid);
				ptr = pack_threadid(ptr, thref);
				*(ptr++) = ',';
				ks->thr_query++;
				if (ks->thr_query % KGDB_MAX_THREAD_QUERY == 0)
					finished = 1;
			}
			i++;
		} while_each_thread(g, p);

		*(--ptr) = '\0';
		break;

	case 'C':
		/* Current thread id */
		strcpy(remcom_out_buffer, "QC");
		ks->threadid = shadow_pid(current->pid);
		int_to_threadref(thref, ks->threadid);
		pack_threadid(remcom_out_buffer + 2, thref);
		break;
	case 'T':
		if (memcmp(remcom_in_buffer + 1, "ThreadExtraInfo,", 16))
			break;

		ks->threadid = 0;
		ptr = remcom_in_buffer + 17;
		kgdb_hex2long(&ptr, &ks->threadid);
		if (!getthread(ks->linux_regs, ks->threadid)