diff --git a/sys/amd64/amd64/amd64-gdbstub.c b/sys/amd64/amd64/amd64-gdbstub.c
new file mode 100644
index 000000000000..41b72afaff3c
--- /dev/null
+++ b/sys/amd64/amd64/amd64-gdbstub.c
@@ -0,0 +1,583 @@
+/****************************************************************************
+
+		THIS SOFTWARE IS NOT COPYRIGHTED
+
+   HP offers the following for use in the public domain.  HP makes no
+   warranty with regard to the software or it's performance and the
+   user accepts the software "AS IS" with all faults.
+
+   HP DISCLAIMS ANY WARRANTIES, EXPRESS OR IMPLIED, WITH REGARD
+   TO THIS SOFTWARE INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+   OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+
+****************************************************************************/
+
+/****************************************************************************
+ *  Header: remcom.c,v 1.34 91/03/09 12:29:49 glenne Exp $
+ *
+ *  Module name: remcom.c $
+ *  Revision: 1.34 $
+ *  Date: 91/03/09 12:29:49 $
+ *  Contributor:     Lake Stevens Instrument Division$
+ *
+ *  Description:     low level support for gdb debugger. $
+ *
+ *  Considerations:  only works on target hardware $
+ *
+ *  Written by:      Glenn Engel $
+ *  ModuleState:     Experimental $
+ *
+ *  NOTES:           See Below $
+ *
+ *  Modified for FreeBSD by Stu Grossman.
+ *
+ *  To enable debugger support, two things need to happen.  One, a
+ *  call to set_debug_traps() is necessary in order to allow any breakpoints
+ *  or error conditions to be properly intercepted and reported to gdb.
+ *  Two, a breakpoint needs to be generated to begin communication.  This
+ *  is most easily accomplished by a call to breakpoint().  Breakpoint()
+ *  simulates a breakpoint by executing a trap #1.
+ *
+ *  The external function exceptionHandler() is
+ *  used to attach a specific handler to a specific 386 vector number.
+ *  It should use the same privilege level it runs at.  It should
+ *  install it as an interrupt gate so that interrupts are masked
+ *  while the handler runs.
+ *  Also, need to assign exceptionHook and oldExceptionHook.
+ *
+ *  Because gdb will sometimes write to the stack area to execute function
+ *  calls, this program cannot rely on using the supervisor stack so it
+ *  uses it's own stack area reserved in the int array remcomStack.
+ *
+ *************
+ *
+ *    The following gdb commands are supported:
+ *
+ * command          function                               Return value
+ *
+ *    g             return the value of the CPU registers  hex data or ENN
+ *    G             set the value of the CPU registers     OK or ENN
+ *
+ *    mAA..AA,LLLL  Read LLLL bytes at address AA..AA      hex data or ENN
+ *    MAA..AA,LLLL: Write LLLL bytes at address AA.AA      OK or ENN
+ *
+ *    c             Resume at current address              SNN   ( signal NN)
+ *    cAA..AA       Continue at address AA..AA             SNN
+ *
+ *    s             Step one instruction                   SNN
+ *    sAA..AA       Step one instruction from AA..AA       SNN
+ *
+ *    k             kill
+ *
+ *    ?             What was the last sigval ?             SNN   (signal NN)
+ *
+ * All commands and responses are sent with a packet which includes a
+ * checksum.  A packet consists of
+ *
+ * $<packet info>#<checksum>.
+ *
+ * where
+ * <packet info> :: <characters representing the command or response>
+ * <checksum>    :: < two hex digits computed as modulo 256 sum of <packetinfo>>
+ *
+ * When a packet is received, it is first acknowledged with either '+' or '-'.
+ * '+' indicates a successful transfer.  '-' indicates a failed transfer.
+ *
+ * Example:
+ *
+ * Host:                  Reply:
+ * $m0,10#2a               +$00010203040506070809101112131415#42
+ *
+ ****************************************************************************/
+
+#include <sys/types.h>
+#include <setjmp.h>
+#include <stdio.h>
+#include <string.h>
+#include <machine/db_machdep.h>
+#include <machine/trap.h>
+#include <machine/psl.h>
+
+/************************************************************************/
+
+void		gdb_handle_exception (db_regs_t *, int, int);
+
+extern jmp_buf	db_jmpbuf;
+extern void	db_read_bytes (vm_offset_t addr, int size, char *data);
+extern void	db_write_bytes (vm_offset_t addr, int size, char *data);
+extern void	siocnputc (dev_t, int c);
+extern int	siocngetc (dev_t);
+
+/************************************************************************/
+/* BUFMAX defines the maximum number of characters in inbound/outbound buffers*/
+/* at least NUMREGBYTES*2 are needed for register packets */
+#define BUFMAX 400
+
+/* Create private copies of common functions used by the stub.  This prevents
+   nasty interactions between app code and the stub (for instance if user steps
+   into strlen, etc..) */
+
+static int
+strlen (const char *s)
+{
+  const char *s1 = s;
+
+  while (*s1++ != '\000');
+
+  return s1 - s;
+}
+
+static char *
+strcpy (char *dst, const char *src)
+{
+  char *retval = dst;
+
+  while ((*dst++ = *src++) != '\000');
+
+  return retval;
+}
+
+static int
+putDebugChar (int c)		/* write a single character      */
+{
+  siocnputc (NULL, c);
+  return 1;
+}
+
+static int
+getDebugChar (void)		/* read and return a single char */
+{
+  return siocngetc (NULL);
+}
+
+static const char hexchars[]="0123456789abcdef";
+
+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 $<data>#<checksum>     */
+static void
+getpacket (char *buffer)
+{
+  unsigned char checksum;
+  unsigned char xmitcsum;
+  int i;
+  int count;
+  unsigned char ch;
+
+  do
+    {
+      /* wait around for the start character, ignore all other characters */
+
+      while ((ch = (getDebugChar () & 0x7f)) != '$');
+
+      checksum = 0;
+      xmitcsum = -1;
+
+      count = 0;
+
+      /* now, read until a # or end of buffer is found */
+
+      while (count < BUFMAX)
+	{
+	  ch = getDebugChar () & 0x7f;
+	  if (ch == '#')
+	    break;
+	  checksum = checksum + ch;
+	  buffer[count] = ch;
+	  count = count + 1;
+	}
+      buffer[count] = 0;
+
+      if (ch == '#')
+	{
+	  xmitcsum = hex (getDebugChar () & 0x7f) << 4;
+	  xmitcsum += hex (getDebugChar () & 0x7f);
+
+	  if (checksum != xmitcsum)
+	    putDebugChar ('-');  /* failed checksum */
+	  else
+	    {
+	      putDebugChar ('+'); /* successful transfer */
+	      /* if a sequence char is present, reply the sequence ID */
+	      if (buffer[2] == ':')
+		{
+		  putDebugChar (buffer[0]);
+		  putDebugChar (buffer[1]);
+
+		  /* remove sequence chars from buffer */
+
+		  count = strlen (buffer);
+		  for (i=3; i <= count; i++)
+		    buffer[i-3] = buffer[i];
+		}
+	    }
+	}
+    }
+  while (checksum != xmitcsum);
+}
+
+/* send the packet in buffer.  */
+
+static void
+putpacket (char *buffer)
+{
+  unsigned char checksum;
+  int count;
+  unsigned char ch;
+
+  /*  $<packet info>#<checksum>. */
+  do
+    {
+      putDebugChar ('$');
+      checksum = 0;
+      count = 0;
+
+      while (ch=buffer[count])
+	{
+	  putDebugChar (ch);
+	  checksum += ch;
+	  count += 1;
+	}
+
+      putDebugChar ('#');
+      putDebugChar (hexchars[checksum >> 4]);
+      putDebugChar (hexchars[checksum & 0xf]);
+    }
+  while ((getDebugChar () & 0x7f) != '+');
+}
+
+static char  remcomInBuffer[BUFMAX];
+static char  remcomOutBuffer[BUFMAX];
+
+static int
+get_char (vm_offset_t addr)
+{
+  char data;
+
+  if (setjmp (db_jmpbuf))
+    return -1;
+
+  db_read_bytes (addr, 1, &data);
+
+  return data & 0xff;
+}
+
+static int
+set_char (vm_offset_t addr, int val)
+{
+  char data;
+
+  if (setjmp (db_jmpbuf))
+    return -1;
+
+  data = val;
+
+  db_write_bytes (addr, 1, &data);
+  return 0;
+}
+
+/* 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 char *
+mem2hex (vm_offset_t mem, char *buf, int count)
+{
+      int i;
+      int ch;
+
+      for (i=0;i<count;i++) {
+          ch = get_char (mem++);
+	  if (ch == -1)
+	    return NULL;
+          *buf++ = hexchars[ch >> 4];
+          *buf++ = hexchars[ch % 16];
+      }
+      *buf = 0;
+      return(buf);
+}
+
+/* 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 char *
+hex2mem (char *buf, vm_offset_t mem, int count)
+{
+      int i;
+      int ch;
+      int rv;
+
+      for (i=0;i<count;i++) {
+          ch = hex(*buf++) << 4;
+          ch = ch + hex(*buf++);
+          rv = set_char (mem++, ch);
+	  if (rv == -1)
+	    return NULL;
+      }
+      return(buf);
+}
+
+/* this function takes the 386 exception vector and attempts to
+   translate this number into a unix compatible signal value */
+static int
+computeSignal (int exceptionVector)
+{
+  int sigval;
+  switch (exceptionVector & ~T_USER)
+    {
+    case 0: sigval = 8; break; /* divide by zero */
+    case 1: sigval = 5; break; /* debug exception */
+    case 3: sigval = 5; break; /* breakpoint */
+    case 4: sigval = 16; break; /* into instruction (overflow) */
+    case 5: sigval = 16; break; /* bound instruction */
+    case 6: sigval = 4; break; /* Invalid opcode */
+    case 7: sigval = 8; break; /* coprocessor not available */
+    case 8: sigval = 7; break; /* double fault */
+    case 9: sigval = 11; break; /* coprocessor segment overrun */
+    case 10: sigval = 5; break; /* Invalid TSS (also single-step) */
+    case 11: sigval = 11; break; /* Segment not present */
+    case 12: sigval = 11; break; /* stack exception */
+    case 13: sigval = 11; break; /* general protection */
+    case 14: sigval = 11; break; /* page fault */
+    case 16: sigval = 7; break; /* coprocessor error */
+    default:
+      sigval = 7;         /* "software generated"*/
+    }
+  return (sigval);
+}
+
+/*
+ * While we find nice hex chars, build an int.
+ * Return number of chars processed.
+ */
+
+static int
+hexToInt(char **ptr, int *intValue)
+{
+    int numChars = 0;
+    int hexValue;
+
+    *intValue = 0;
+
+    while (**ptr)
+    {
+        hexValue = hex(**ptr);
+        if (hexValue >=0)
+        {
+            *intValue = (*intValue <<4) | hexValue;
+            numChars ++;
+        }
+        else
+            break;
+
+        (*ptr)++;
+    }
+
+    return (numChars);
+}
+
+#define NUMREGBYTES (sizeof registers)
+#define PC 8
+#define SP 4
+#define FP 5
+#define NUM_REGS 14
+
+/*
+ * This function does all command procesing for interfacing to gdb.
+ */
+void
+gdb_handle_exception (db_regs_t *raw_regs, int type, int code)
+{
+  int    sigval;
+  int    addr, length;
+  char * ptr;
+  struct i386regs {
+    unsigned int eax;
+    unsigned int ecx;
+    unsigned int edx;
+    unsigned int ebx;
+    unsigned int esp;
+    unsigned int ebp;
+    unsigned int esi;
+    unsigned int edi;
+    unsigned int eip;
+    unsigned int eflags;
+    unsigned int cs;
+    unsigned int ss;
+    unsigned int ds;
+    unsigned int es;
+  };
+  struct i386regs registers;
+
+  registers.eax = raw_regs->tf_eax;
+  registers.ebx = raw_regs->tf_ebx;
+  registers.ecx = raw_regs->tf_ecx;
+  registers.edx = raw_regs->tf_edx;
+
+  registers.esp = raw_regs->tf_esp;
+  registers.ebp = raw_regs->tf_ebp;
+  registers.esi = raw_regs->tf_esi;
+  registers.edi = raw_regs->tf_edi;
+
+  registers.eip = raw_regs->tf_eip;
+  registers.eflags = raw_regs->tf_eflags;
+
+  registers.cs = raw_regs->tf_cs;
+  registers.ss = raw_regs->tf_ss;
+  registers.ds = raw_regs->tf_ds;
+  registers.es = raw_regs->tf_es;
+
+  /* reply to host that an exception has occurred */
+  sigval = computeSignal (type);
+  ptr = remcomOutBuffer;
+
+  *ptr++ = 'T';
+  *ptr++ = hexchars[sigval >> 4];
+  *ptr++ = hexchars[sigval & 0xf];
+
+  *ptr++ = hexchars[PC >> 4];
+  *ptr++ = hexchars[PC & 0xf];
+  *ptr++ = ':';
+  ptr = mem2hex ((vm_offset_t)&registers.eip, ptr, 4);
+  *ptr++ = ';';
+
+  *ptr++ = hexchars[FP >> 4];
+  *ptr++ = hexchars[FP & 0xf];
+  *ptr++ = ':';
+  ptr = mem2hex ((vm_offset_t)&registers.ebp, ptr, 4);
+  *ptr++ = ';';
+
+  *ptr++ = hexchars[SP >> 4];
+  *ptr++ = hexchars[SP & 0xf];
+  *ptr++ = ':';
+  ptr = mem2hex ((vm_offset_t)&registers.esp, ptr, 4);
+  *ptr++ = ';';
+
+  *ptr++ = 0;
+
+  putpacket (remcomOutBuffer);
+
+  while (1)
+    {
+      remcomOutBuffer[0] = 0;
+
+      getpacket (remcomInBuffer);
+      switch (remcomInBuffer[0]) 
+	{
+	case '?':
+	  remcomOutBuffer[0] = 'S';
+	  remcomOutBuffer[1] = hexchars[sigval >> 4];
+	  remcomOutBuffer[2] = hexchars[sigval % 16];
+	  remcomOutBuffer[3] = 0;
+	  break;
+
+	case 'g':		/* return the value of the CPU registers */
+	  mem2hex ((vm_offset_t)&registers, remcomOutBuffer, NUMREGBYTES);
+	  break;
+
+	case 'G':		/* set the value of the CPU registers - return OK */
+	  hex2mem (&remcomInBuffer[1], (vm_offset_t)&registers, NUMREGBYTES);
+	  strcpy (remcomOutBuffer, "OK");
+	  break;
+
+	case 'P':		/* Set the value of one register */
+	  {
+	    int regno;
+
+	    ptr = &remcomInBuffer[1];
+
+	    if (hexToInt (&ptr, &regno)
+		&& *ptr++ == '='
+		&& regno < NUM_REGS)
+	      {
+		hex2mem (ptr, (vm_offset_t)&registers + regno * 4, 4);
+		strcpy(remcomOutBuffer,"OK");
+	      }
+	    else
+	      strcpy (remcomOutBuffer, "P01");
+	    break;
+	  }
+	case 'm':	/* mAA..AA,LLLL  Read LLLL bytes at address AA..AA */
+	  /* Try to read %x,%x.  */
+
+	  ptr = &remcomInBuffer[1];
+
+	  if (hexToInt (&ptr, &addr)
+	      && *(ptr++) == ','
+	      && hexToInt (&ptr, &length))
+	    {
+	      if (mem2hex((vm_offset_t) addr, remcomOutBuffer, length) == NULL)
+		strcpy (remcomOutBuffer, "E03");
+	      break;
+	    }
+	  else
+	    strcpy (remcomOutBuffer, "E01");
+	  break;
+
+	case 'M': /* MAA..AA,LLLL: Write LLLL bytes at address AA.AA return OK */
+
+	  /* Try to read '%x,%x:'.  */
+
+	  ptr = &remcomInBuffer[1];
+
+	  if (hexToInt(&ptr,&addr)
+	      && *(ptr++) == ','
+	      && hexToInt(&ptr, &length)
+	      && *(ptr++) == ':')
+	    {
+	      if (hex2mem(ptr, (vm_offset_t) addr, length) == NULL)
+		strcpy (remcomOutBuffer, "E03");
+	      else
+		strcpy (remcomOutBuffer, "OK");
+	    }
+	  else
+	    strcpy (remcomOutBuffer, "E02");
+	  break;
+
+	  /* cAA..AA    Continue at address AA..AA(optional) */
+	  /* sAA..AA   Step one instruction from AA..AA(optional) */
+	case 'c' :
+	case 's' :
+	  /* try to read optional parameter, pc unchanged if no parm */
+
+	  ptr = &remcomInBuffer[1];
+	  if (hexToInt(&ptr,&addr))
+	    registers.eip = addr;
+
+
+	  /* set the trace bit if we're stepping */
+	  if (remcomInBuffer[0] == 's')
+	    registers.eflags |= PSL_T;
+	  else
+	    registers.eflags &= ~PSL_T;
+
+	  raw_regs->tf_eax = registers.eax;
+	  raw_regs->tf_ebx = registers.ebx;
+	  raw_regs->tf_ecx = registers.ecx;
+	  raw_regs->tf_edx = registers.edx;
+
+	  raw_regs->tf_esp = registers.esp;
+	  raw_regs->tf_ebp = registers.ebp;
+	  raw_regs->tf_esi = registers.esi;
+	  raw_regs->tf_edi = registers.edi;
+
+	  raw_regs->tf_eip = registers.eip;
+	  raw_regs->tf_eflags = registers.eflags;
+
+	  raw_regs->tf_cs = registers.cs;
+	  raw_regs->tf_ss = registers.ss;
+	  raw_regs->tf_ds = registers.ds;
+	  raw_regs->tf_es = registers.es;
+	  return;
+
+	} /* switch */
+
+      /* reply to the request */
+      putpacket (remcomOutBuffer);
+    }
+}
diff --git a/sys/amd64/amd64/db_interface.c b/sys/amd64/amd64/db_interface.c
index db7e06031524..159400c4dbae 100644
--- a/sys/amd64/amd64/db_interface.c
+++ b/sys/amd64/amd64/db_interface.c
@@ -23,7 +23,7 @@
  * any improvements or extensions that they make and grant Carnegie the
  * rights to redistribute these changes.
  *
- *	$Id: db_interface.c,v 1.18 1996/04/07 18:34:59 bde Exp $
+ *	$Id: db_interface.c,v 1.19 1996/05/03 21:00:51 phk Exp $
  */
 
 /*
@@ -48,6 +48,7 @@
 #include <setjmp.h>
 
 static int	db_active = 0;
+extern void	gdb_handle_exception __P((db_regs_t *, int, int));
 
 db_regs_t ddb_regs;
 
@@ -93,7 +94,7 @@ kdb_trap(type, code, regs)
 	 * our breakpoints by disarming our breakpoints and fixing up
 	 * %eip.
 	 */
-	if (cons_unavail) {
+	if (cons_unavail && !(boothowto & RB_GDB)) {
 		if (type == T_TRCTRAP) {
 			regs->tf_eflags &= ~PSL_T;
 			return (1);
@@ -133,7 +134,10 @@ kdb_trap(type, code, regs)
 
 	db_active++;
 	cnpollc(TRUE);
-	db_trap(type, code);
+	if (boothowto & RB_GDB)
+	    gdb_handle_exception(&ddb_regs, type, code);
+	else
+	    db_trap(type, code);
 	cnpollc(FALSE);
 	db_active--;
 
@@ -267,7 +271,7 @@ Debugger(msg)
 	 * OK if the call is for the debugger hotkey but not if the call
 	 * is a weak form of panicing.
 	 */
-	if (cons_unavail)
+	if (cons_unavail & !(boothowto & RB_GDB))
 		return;
 
 	if (!in_Debugger) {
diff --git a/sys/conf/files.i386 b/sys/conf/files.i386
index 9b217436cca4..090296cc41f7 100644
--- a/sys/conf/files.i386
+++ b/sys/conf/files.i386
@@ -1,7 +1,7 @@
 # This file tells config what files go into building a kernel,
 # files marked standard are always included.
 #
-#	$Id: files.i386,v 1.137 1996/07/05 18:49:01 jhay Exp $
+#	$Id: files.i386,v 1.138 1996/07/08 19:44:30 wollman Exp $
 #
 aic7xxx_asm			optional	ahc	device-driver	   \
 	dependency 	"$S/dev/aic7xxx/aic7xxx_asm.c"			   \
@@ -40,6 +40,7 @@ i386/i386/cons.c		standard
 i386/i386/db_disasm.c		optional	ddb
 i386/i386/db_interface.c	optional	ddb
 i386/i386/db_trace.c		optional	ddb
+i386/i386/i386-gdbstub.c	optional	ddb
 i386/i386/exception.s		standard
 i386/i386/identcpu.c		standard
 i386/i386/in_cksum.c		optional	inet
diff --git a/sys/i386/boot/biosboot/boot.c b/sys/i386/boot/biosboot/boot.c
index 2decc57d0ea7..fc190003bfc3 100644
--- a/sys/i386/boot/biosboot/boot.c
+++ b/sys/i386/boot/biosboot/boot.c
@@ -24,7 +24,7 @@
  * the rights to redistribute these changes.
  *
  *	from: Mach, [92/04/03  16:51:14  rvb]
- *	$Id: boot.c,v 1.52 1996/07/09 02:28:20 julian Exp $
+ *	$Id: boot.c,v 1.53 1996/07/12 05:25:45 bde Exp $
  */
 
 
@@ -332,6 +332,8 @@ nextarg:
 					if (*howto & RB_SERIAL)
 						init_serial();
 				}
+				if (c == 'g')
+					*howto |= RB_GDB;
 				if (c == 'r')
 					*howto |= RB_DFLTROOT;
 				if (c == 's')
diff --git a/sys/i386/boot/dosboot/fbsdboot.c b/sys/i386/boot/dosboot/fbsdboot.c
index fd77aae814d1..4bb18e415b68 100644
--- a/sys/i386/boot/dosboot/fbsdboot.c
+++ b/sys/i386/boot/dosboot/fbsdboot.c
@@ -94,6 +94,7 @@ int main(int argc, char *argv[])
 				case 'a': howto |= RB_ASKNAME; break;
 				case 'c': howto |= RB_CONFIG; break;
 				case 'd': howto |= RB_KDB; break;
+				case 'g': howto |= RB_GDB; break;
 				case 'v': howto |= RB_VERBOSE; break;
 				case 'C': howto |= RB_CDROM; break;
 				case 'D': dos = 1; kernel = "c:\\kernel"; break;
diff --git a/sys/i386/boot/dosboot/reboot.h b/sys/i386/boot/dosboot/reboot.h
index 51b5f1f98f75..c21858a75cfc 100644
--- a/sys/i386/boot/dosboot/reboot.h
+++ b/sys/i386/boot/dosboot/reboot.h
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)reboot.h	8.1 (Berkeley) 6/2/93
- * $Id: reboot.h,v 1.7 1994/11/26 09:08:40 phk Exp $
+ * $Id: reboot.h,v 1.2 1995/04/27 18:22:32 phk Exp $
  */
 
 #ifndef _SYS_REBOOT_H_
@@ -56,8 +56,10 @@
 #define	RB_MINIROOT	0x200	/* mini-root present in memory at boot time */
 #define RB_CONFIG	0x400	/* invoke user configuration routing */
 #define RB_VERBOSE	0x800	/* print all potentially useful info */
-#define	RB_SERIAL	0x1000	/* user serial port as console */
-#define	RB_CDROM	0x2000	/* use cdrom as root */
+#define RB_SERIAL	0x1000	/* user serial port as console */
+#define RB_CDROM	0x2000	/* use cdrom as root */
+#define RB_POWEROFF     0x4000  /* if you can, turn the power off */
+#define RB_GDB          0x8000  /* use GDB remote debugger instead of DDB */
 
 #define	RB_BOOTINFO	0x80000000	/* have `struct bootinfo *' arg */
 
diff --git a/sys/i386/boot/netboot/bootmenu.c b/sys/i386/boot/netboot/bootmenu.c
index d8f23306379b..7e5b0157001c 100644
--- a/sys/i386/boot/netboot/bootmenu.c
+++ b/sys/i386/boot/netboot/bootmenu.c
@@ -299,6 +299,7 @@ cmd_flags(buf)
 	case 'b':	flags |= RB_HALT; break;
 	case 'c':	flags |= RB_CONFIG; break;
 	case 'd':	flags |= RB_KDB; break;
+	case 'g':	flags |= RB_GDB; break;
 	case 'h':	flags ^= RB_SERIAL; break;
 	case 's':	flags |= RB_SINGLE; break;
 	case 'v':	flags |= RB_VERBOSE; break;
diff --git a/sys/i386/conf/files.i386 b/sys/i386/conf/files.i386
index 9b217436cca4..090296cc41f7 100644
--- a/sys/i386/conf/files.i386
+++ b/sys/i386/conf/files.i386
@@ -1,7 +1,7 @@
 # This file tells config what files go into building a kernel,
 # files marked standard are always included.
 #
-#	$Id: files.i386,v 1.137 1996/07/05 18:49:01 jhay Exp $
+#	$Id: files.i386,v 1.138 1996/07/08 19:44:30 wollman Exp $
 #
 aic7xxx_asm			optional	ahc	device-driver	   \
 	dependency 	"$S/dev/aic7xxx/aic7xxx_asm.c"			   \
@@ -40,6 +40,7 @@ i386/i386/cons.c		standard
 i386/i386/db_disasm.c		optional	ddb
 i386/i386/db_interface.c	optional	ddb
 i386/i386/db_trace.c		optional	ddb
+i386/i386/i386-gdbstub.c	optional	ddb
 i386/i386/exception.s		standard
 i386/i386/identcpu.c		standard
 i386/i386/in_cksum.c		optional	inet
diff --git a/sys/i386/i386/db_interface.c b/sys/i386/i386/db_interface.c
index db7e06031524..159400c4dbae 100644
--- a/sys/i386/i386/db_interface.c
+++ b/sys/i386/i386/db_interface.c
@@ -23,7 +23,7 @@
  * any improvements or extensions that they make and grant Carnegie the
  * rights to redistribute these changes.
  *
- *	$Id: db_interface.c,v 1.18 1996/04/07 18:34:59 bde Exp $
+ *	$Id: db_interface.c,v 1.19 1996/05/03 21:00:51 phk Exp $
  */
 
 /*
@@ -48,6 +48,7 @@
 #include <setjmp.h>
 
 static int	db_active = 0;
+extern void	gdb_handle_exception __P((db_regs_t *, int, int));
 
 db_regs_t ddb_regs;
 
@@ -93,7 +94,7 @@ kdb_trap(type, code, regs)
 	 * our breakpoints by disarming our breakpoints and fixing up
 	 * %eip.
 	 */
-	if (cons_unavail) {
+	if (cons_unavail && !(boothowto & RB_GDB)) {
 		if (type == T_TRCTRAP) {
 			regs->tf_eflags &= ~PSL_T;
 			return (1);
@@ -133,7 +134,10 @@ kdb_trap(type, code, regs)
 
 	db_active++;
 	cnpollc(TRUE);
-	db_trap(type, code);
+	if (boothowto & RB_GDB)
+	    gdb_handle_exception(&ddb_regs, type, code);
+	else
+	    db_trap(type, code);
 	cnpollc(FALSE);
 	db_active--;
 
@@ -267,7 +271,7 @@ Debugger(msg)
 	 * OK if the call is for the debugger hotkey but not if the call
 	 * is a weak form of panicing.
 	 */
-	if (cons_unavail)
+	if (cons_unavail & !(boothowto & RB_GDB))
 		return;
 
 	if (!in_Debugger) {
diff --git a/sys/i386/i386/i386-gdbstub.c b/sys/i386/i386/i386-gdbstub.c
new file mode 100644
index 000000000000..41b72afaff3c
--- /dev/null
+++ b/sys/i386/i386/i386-gdbstub.c
@@ -0,0 +1,583 @@
+/****************************************************************************
+
+		THIS SOFTWARE IS NOT COPYRIGHTED
+
+   HP offers the following for use in the public domain.  HP makes no
+   warranty with regard to the software or it's performance and the
+   user accepts the software "AS IS" with all faults.
+
+   HP DISCLAIMS ANY WARRANTIES, EXPRESS OR IMPLIED, WITH REGARD
+   TO THIS SOFTWARE INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+   OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+
+****************************************************************************/
+
+/****************************************************************************
+ *  Header: remcom.c,v 1.34 91/03/09 12:29:49 glenne Exp $
+ *
+ *  Module name: remcom.c $
+ *  Revision: 1.34 $
+ *  Date: 91/03/09 12:29:49 $
+ *  Contributor:     Lake Stevens Instrument Division$
+ *
+ *  Description:     low level support for gdb debugger. $
+ *
+ *  Considerations:  only works on target hardware $
+ *
+ *  Written by:      Glenn Engel $
+ *  ModuleState:     Experimental $
+ *
+ *  NOTES:           See Below $
+ *
+ *  Modified for FreeBSD by Stu Grossman.
+ *
+ *  To enable debugger support, two things need to happen.  One, a
+ *  call to set_debug_traps() is necessary in order to allow any breakpoints
+ *  or error conditions to be properly intercepted and reported to gdb.
+ *  Two, a breakpoint needs to be generated to begin communication.  This
+ *  is most easily accomplished by a call to breakpoint().  Breakpoint()
+ *  simulates a breakpoint by executing a trap #1.
+ *
+ *  The external function exceptionHandler() is
+ *  used to attach a specific handler to a specific 386 vector number.
+ *  It should use the same privilege level it runs at.  It should
+ *  install it as an interrupt gate so that interrupts are masked
+ *  while the handler runs.
+ *  Also, need to assign exceptionHook and oldExceptionHook.
+ *
+ *  Because gdb will sometimes write to the stack area to execute function
+ *  calls, this program cannot rely on using the supervisor stack so it
+ *  uses it's own stack area reserved in the int array remcomStack.
+ *
+ *************
+ *
+ *    The following gdb commands are supported:
+ *
+ * command          function                               Return value
+ *
+ *    g             return the value of the CPU registers  hex data or ENN
+ *    G             set the value of the CPU registers     OK or ENN
+ *
+ *    mAA..AA,LLLL  Read LLLL bytes at address AA..AA      hex data or ENN
+ *    MAA..AA,LLLL: Write LLLL bytes at address AA.AA      OK or ENN
+ *
+ *    c             Resume at current address              SNN   ( signal NN)
+ *    cAA..AA       Continue at address AA..AA             SNN
+ *
+ *    s             Step one instruction                   SNN
+ *    sAA..AA       Step one instruction from AA..AA       SNN
+ *
+ *    k             kill
+ *
+ *    ?             What was the last sigval ?             SNN   (signal NN)
+ *
+ * All commands and responses are sent with a packet which includes a
+ * checksum.  A packet consists of
+ *
+ * $<packet info>#<checksum>.
+ *
+ * where
+ * <packet info> :: <characters representing the command or response>
+ * <checksum>    :: < two hex digits computed as modulo 256 sum of <packetinfo>>
+ *
+ * When a packet is received, it is first acknowledged with either '+' or '-'.
+ * '+' indicates a successful transfer.  '-' indicates a failed transfer.
+ *
+ * Example:
+ *
+ * Host:                  Reply:
+ * $m0,10#2a               +$00010203040506070809101112131415#42
+ *
+ ****************************************************************************/
+
+#include <sys/types.h>
+#include <setjmp.h>
+#include <stdio.h>
+#include <string.h>
+#include <machine/db_machdep.h>
+#include <machine/trap.h>
+#include <machine/psl.h>
+
+/************************************************************************/
+
+void		gdb_handle_exception (db_regs_t *, int, int);
+
+extern jmp_buf	db_jmpbuf;
+extern void	db_read_bytes (vm_offset_t addr, int size, char *data);
+extern void	db_write_bytes (vm_offset_t addr, int size, char *data);
+extern void	siocnputc (dev_t, int c);
+extern int	siocngetc (dev_t);
+
+/************************************************************************/
+/* BUFMAX defines the maximum number of characters in inbound/outbound buffers*/
+/* at least NUMREGBYTES*2 are needed for register packets */
+#define BUFMAX 400
+
+/* Create private copies of common functions used by the stub.  This prevents
+   nasty interactions between app code and the stub (for instance if user steps
+   into strlen, etc..) */
+
+static int
+strlen (const char *s)
+{
+  const char *s1 = s;
+
+  while (*s1++ != '\000');
+
+  return s1 - s;
+}
+
+static char *
+strcpy (char *dst, const char *src)
+{
+  char *retval = dst;
+
+  while ((*dst++ = *src++) != '\000');
+
+  return retval;
+}
+
+static int
+putDebugChar (int c)		/* write a single character      */
+{
+  siocnputc (NULL, c);
+  return 1;
+}
+
+static int
+getDebugChar (void)		/* read and return a single char */
+{
+  return siocngetc (NULL);
+}
+
+static const char hexchars[]="0123456789abcdef";
+
+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 $<data>#<checksum>     */
+static void
+getpacket (char *buffer)
+{
+  unsigned char checksum;
+  unsigned char xmitcsum;
+  int i;
+  int count;
+  unsigned char ch;
+
+  do
+    {
+      /* wait around for the start character, ignore all other characters */
+
+      while ((ch = (getDebugChar () & 0x7f)) != '$');
+
+      checksum = 0;
+      xmitcsum = -1;
+
+      count = 0;
+
+      /* now, read until a # or end of buffer is found */
+
+      while (count < BUFMAX)
+	{
+	  ch = getDebugChar () & 0x7f;
+	  if (ch == '#')
+	    break;
+	  checksum = checksum + ch;
+	  buffer[count] = ch;
+	  count = count + 1;
+	}
+      buffer[count] = 0;
+
+      if (ch == '#')
+	{
+	  xmitcsum = hex (getDebugChar () & 0x7f) << 4;
+	  xmitcsum += hex (getDebugChar () & 0x7f);
+
+	  if (checksum != xmitcsum)
+	    putDebugChar ('-');  /* failed checksum */
+	  else
+	    {
+	      putDebugChar ('+'); /* successful transfer */
+	      /* if a sequence char is present, reply the sequence ID */
+	      if (buffer[2] == ':')
+		{
+		  putDebugChar (buffer[0]);
+		  putDebugChar (buffer[1]);
+
+		  /* remove sequence chars from buffer */
+
+		  count = strlen (buffer);
+		  for (i=3; i <= count; i++)
+		    buffer[i-3] = buffer[i];
+		}
+	    }
+	}
+    }
+  while (checksum != xmitcsum);
+}
+
+/* send the packet in buffer.  */
+
+static void
+putpacket (char *buffer)
+{
+  unsigned char checksum;
+  int count;
+  unsigned char ch;
+
+  /*  $<packet info>#<checksum>. */
+  do
+    {
+      putDebugChar ('$');
+      checksum = 0;
+      count = 0;
+
+      while (ch=buffer[count])
+	{
+	  putDebugChar (ch);
+	  checksum += ch;
+	  count += 1;
+	}
+
+      putDebugChar ('#');
+      putDebugChar (hexchars[checksum >> 4]);
+      putDebugChar (hexchars[checksum & 0xf]);
+    }
+  while ((getDebugChar () & 0x7f) != '+');
+}
+
+static char  remcomInBuffer[BUFMAX];
+static char  remcomOutBuffer[BUFMAX];
+
+static int
+get_char (vm_offset_t addr)
+{
+  char data;
+
+  if (setjmp (db_jmpbuf))
+    return -1;
+
+  db_read_bytes (addr, 1, &data);
+
+  return data & 0xff;
+}
+
+static int
+set_char (vm_offset_t addr, int val)
+{
+  char data;
+
+  if (setjmp (db_jmpbuf))
+    return -1;
+
+  data = val;
+
+  db_write_bytes (addr, 1, &data);
+  return 0;
+}
+
+/* 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 char *
+mem2hex (vm_offset_t mem, char *buf, int count)
+{
+      int i;
+      int ch;
+
+      for (i=0;i<count;i++) {
+          ch = get_char (mem++);
+	  if (ch == -1)
+	    return NULL;
+          *buf++ = hexchars[ch >> 4];
+          *buf++ = hexchars[ch % 16];
+      }
+      *buf = 0;
+      return(buf);
+}
+
+/* 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 char *
+hex2mem (char *buf, vm_offset_t mem, int count)
+{
+      int i;
+      int ch;
+      int rv;
+
+      for (i=0;i<count;i++) {
+          ch = hex(*buf++) << 4;
+          ch = ch + hex(*buf++);
+          rv = set_char (mem++, ch);
+	  if (rv == -1)
+	    return NULL;
+      }
+      return(buf);
+}
+
+/* this function takes the 386 exception vector and attempts to
+   translate this number into a unix compatible signal value */
+static int
+computeSignal (int exceptionVector)
+{
+  int sigval;
+  switch (exceptionVector & ~T_USER)
+    {
+    case 0: sigval = 8; break; /* divide by zero */
+    case 1: sigval = 5; break; /* debug exception */
+    case 3: sigval = 5; break; /* breakpoint */
+    case 4: sigval = 16; break; /* into instruction (overflow) */
+    case 5: sigval = 16; break; /* bound instruction */
+    case 6: sigval = 4; break; /* Invalid opcode */
+    case 7: sigval = 8; break; /* coprocessor not available */
+    case 8: sigval = 7; break; /* double fault */
+    case 9: sigval = 11; break; /* coprocessor segment overrun */
+    case 10: sigval = 5; break; /* Invalid TSS (also single-step) */
+    case 11: sigval = 11; break; /* Segment not present */
+    case 12: sigval = 11; break; /* stack exception */
+    case 13: sigval = 11; break; /* general protection */
+    case 14: sigval = 11; break; /* page fault */
+    case 16: sigval = 7; break; /* coprocessor error */
+    default:
+      sigval = 7;         /* "software generated"*/
+    }
+  return (sigval);
+}
+
+/*
+ * While we find nice hex chars, build an int.
+ * Return number of chars processed.
+ */
+
+static int
+hexToInt(char **ptr, int *intValue)
+{
+    int numChars = 0;
+    int hexValue;
+
+    *intValue = 0;
+
+    while (**ptr)
+    {
+        hexValue = hex(**ptr);
+        if (hexValue >=0)
+        {
+            *intValue = (*intValue <<4) | hexValue;
+            numChars ++;
+        }
+        else
+            break;
+
+        (*ptr)++;
+    }
+
+    return (numChars);
+}
+
+#define NUMREGBYTES (sizeof registers)
+#define PC 8
+#define SP 4
+#define FP 5
+#define NUM_REGS 14
+
+/*
+ * This function does all command procesing for interfacing to gdb.
+ */
+void
+gdb_handle_exception (db_regs_t *raw_regs, int type, int code)
+{
+  int    sigval;
+  int    addr, length;
+  char * ptr;
+  struct i386regs {
+    unsigned int eax;
+    unsigned int ecx;
+    unsigned int edx;
+    unsigned int ebx;
+    unsigned int esp;
+    unsigned int ebp;
+    unsigned int esi;
+    unsigned int edi;
+    unsigned int eip;
+    unsigned int eflags;
+    unsigned int cs;
+    unsigned int ss;
+    unsigned int ds;
+    unsigned int es;
+  };
+  struct i386regs registers;
+
+  registers.eax = raw_regs->tf_eax;
+  registers.ebx = raw_regs->tf_ebx;
+  registers.ecx = raw_regs->tf_ecx;
+  registers.edx = raw_regs->tf_edx;
+
+  registers.esp = raw_regs->tf_esp;
+  registers.ebp = raw_regs->tf_ebp;
+  registers.esi = raw_regs->tf_esi;
+  registers.edi = raw_regs->tf_edi;
+
+  registers.eip = raw_regs->tf_eip;
+  registers.eflags = raw_regs->tf_eflags;
+
+  registers.cs = raw_regs->tf_cs;
+  registers.ss = raw_regs->tf_ss;
+  registers.ds = raw_regs->tf_ds;
+  registers.es = raw_regs->tf_es;
+
+  /* reply to host that an exception has occurred */
+  sigval = computeSignal (type);
+  ptr = remcomOutBuffer;
+
+  *ptr++ = 'T';
+  *ptr++ = hexchars[sigval >> 4];
+  *ptr++ = hexchars[sigval & 0xf];
+
+  *ptr++ = hexchars[PC >> 4];
+  *ptr++ = hexchars[PC & 0xf];
+  *ptr++ = ':';
+  ptr = mem2hex ((vm_offset_t)&registers.eip, ptr, 4);
+  *ptr++ = ';';
+
+  *ptr++ = hexchars[FP >> 4];
+  *ptr++ = hexchars[FP & 0xf];
+  *ptr++ = ':';
+  ptr = mem2hex ((vm_offset_t)&registers.ebp, ptr, 4);
+  *ptr++ = ';';
+
+  *ptr++ = hexchars[SP >> 4];
+  *ptr++ = hexchars[SP & 0xf];
+  *ptr++ = ':';
+  ptr = mem2hex ((vm_offset_t)&registers.esp, ptr, 4);
+  *ptr++ = ';';
+
+  *ptr++ = 0;
+
+  putpacket (remcomOutBuffer);
+
+  while (1)
+    {
+      remcomOutBuffer[0] = 0;
+
+      getpacket (remcomInBuffer);
+      switch (remcomInBuffer[0]) 
+	{
+	case '?':
+	  remcomOutBuffer[0] = 'S';
+	  remcomOutBuffer[1] = hexchars[sigval >> 4];
+	  remcomOutBuffer[2] = hexchars[sigval % 16];
+	  remcomOutBuffer[3] = 0;
+	  break;
+
+	case 'g':		/* return the value of the CPU registers */
+	  mem2hex ((vm_offset_t)&registers, remcomOutBuffer, NUMREGBYTES);
+	  break;
+
+	case 'G':		/* set the value of the CPU registers - return OK */
+	  hex2mem (&remcomInBuffer[1], (vm_offset_t)&registers, NUMREGBYTES);
+	  strcpy (remcomOutBuffer, "OK");
+	  break;
+
+	case 'P':		/* Set the value of one register */
+	  {
+	    int regno;
+
+	    ptr = &remcomInBuffer[1];
+
+	    if (hexToInt (&ptr, &regno)
+		&& *ptr++ == '='
+		&& regno < NUM_REGS)
+	      {
+		hex2mem (ptr, (vm_offset_t)&registers + regno * 4, 4);
+		strcpy(remcomOutBuffer,"OK");
+	      }
+	    else
+	      strcpy (remcomOutBuffer, "P01");
+	    break;
+	  }
+	case 'm':	/* mAA..AA,LLLL  Read LLLL bytes at address AA..AA */
+	  /* Try to read %x,%x.  */
+
+	  ptr = &remcomInBuffer[1];
+
+	  if (hexToInt (&ptr, &addr)
+	      && *(ptr++) == ','
+	      && hexToInt (&ptr, &length))
+	    {
+	      if (mem2hex((vm_offset_t) addr, remcomOutBuffer, length) == NULL)
+		strcpy (remcomOutBuffer, "E03");
+	      break;
+	    }
+	  else
+	    strcpy (remcomOutBuffer, "E01");
+	  break;
+
+	case 'M': /* MAA..AA,LLLL: Write LLLL bytes at address AA.AA return OK */
+
+	  /* Try to read '%x,%x:'.  */
+
+	  ptr = &remcomInBuffer[1];
+
+	  if (hexToInt(&ptr,&addr)
+	      && *(ptr++) == ','
+	      && hexToInt(&ptr, &length)
+	      && *(ptr++) == ':')
+	    {
+	      if (hex2mem(ptr, (vm_offset_t) addr, length) == NULL)
+		strcpy (remcomOutBuffer, "E03");
+	      else
+		strcpy (remcomOutBuffer, "OK");
+	    }
+	  else
+	    strcpy (remcomOutBuffer, "E02");
+	  break;
+
+	  /* cAA..AA    Continue at address AA..AA(optional) */
+	  /* sAA..AA   Step one instruction from AA..AA(optional) */
+	case 'c' :
+	case 's' :
+	  /* try to read optional parameter, pc unchanged if no parm */
+
+	  ptr = &remcomInBuffer[1];
+	  if (hexToInt(&ptr,&addr))
+	    registers.eip = addr;
+
+
+	  /* set the trace bit if we're stepping */
+	  if (remcomInBuffer[0] == 's')
+	    registers.eflags |= PSL_T;
+	  else
+	    registers.eflags &= ~PSL_T;
+
+	  raw_regs->tf_eax = registers.eax;
+	  raw_regs->tf_ebx = registers.ebx;
+	  raw_regs->tf_ecx = registers.ecx;
+	  raw_regs->tf_edx = registers.edx;
+
+	  raw_regs->tf_esp = registers.esp;
+	  raw_regs->tf_ebp = registers.ebp;
+	  raw_regs->tf_esi = registers.esi;
+	  raw_regs->tf_edi = registers.edi;
+
+	  raw_regs->tf_eip = registers.eip;
+	  raw_regs->tf_eflags = registers.eflags;
+
+	  raw_regs->tf_cs = registers.cs;
+	  raw_regs->tf_ss = registers.ss;
+	  raw_regs->tf_ds = registers.ds;
+	  raw_regs->tf_es = registers.es;
+	  return;
+
+	} /* switch */
+
+      /* reply to the request */
+      putpacket (remcomOutBuffer);
+    }
+}
diff --git a/sys/sys/reboot.h b/sys/sys/reboot.h
index ecf6cb89bd71..d4b5ccbb0540 100644
--- a/sys/sys/reboot.h
+++ b/sys/sys/reboot.h
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)reboot.h	8.3 (Berkeley) 12/13/94
- * $Id: reboot.h,v 1.11 1996/03/11 02:09:55 hsu Exp $
+ * $Id: reboot.h,v 1.12 1996/08/22 03:50:32 julian Exp $
  */
 
 #ifndef _SYS_REBOOT_H_
@@ -58,6 +58,7 @@
 #define	RB_SERIAL	0x1000	/* user serial port as console */
 #define	RB_CDROM	0x2000	/* use cdrom as root */
 #define	RB_POWEROFF	0x4000	/* if you can, turn the power off */
+#define	RB_GDB		0x8000	/* use GDB remote debugger instead of DDB */
 
 #define	RB_BOOTINFO	0x80000000	/* have `struct bootinfo *' arg */