gdb/

2012-03-08  Tristan Gingold  <gingold@adacore.com>

	* sparc-stub.c: Move to stubs/
	* sh-stub.c: Likewise.
	* m68k-stub.c: Likewise.
	* m32r-stub.c: Likewise.
	* i386-stub.c: Likewise.

gdb/stubs/
2012-03-08  Tristan Gingold  <gingold@adacore.com>

	* sparc-stub.c: Move from ..
	* sh-stub.c: Likewise.
	* m68k-stub.c: Likewise.
	* m32r-stub.c: Likewise.
	* i386-stub.c: Likewise.

1 files changed, 1098 insertions, 0 deletions

diff --git a/gdb/stubs/m68k-stub.c b/gdb/stubs/m68k-stub.c
new file mode 100644
index 0000000..4ef4069
--- /dev/null
+++ b/gdb/stubs/m68k-stub.c
@@ -0,0 +1,1098 @@
+/****************************************************************************
+
+		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 $
+ * 
+ *  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 breakpoint instruction
+ *  is hardwired to trap #1 because not to do so is a compatibility problem--
+ *  there either should be a standard breakpoint instruction, or the protocol
+ *  should be extended to provide some means to communicate which breakpoint
+ *  instruction is in use (or have the stub insert the breakpoint).
+ *  
+ *  Some explanation is probably necessary to explain how exceptions are
+ *  handled.  When an exception is encountered the 68000 pushes the current
+ *  program counter and status register onto the supervisor stack and then
+ *  transfers execution to a location specified in it's vector table.
+ *  The handlers for the exception vectors are hardwired to jmp to an address
+ *  given by the relation:  (exception - 256) * 6.  These are decending 
+ *  addresses starting from -6, -12, -18, ...  By allowing 6 bytes for
+ *  each entry, a jsr, jmp, bsr, ... can be used to enter the exception 
+ *  handler.  Using a jsr to handle an exception has an added benefit of
+ *  allowing a single handler to service several exceptions and use the
+ *  return address as the key differentiation.  The vector number can be
+ *  computed from the return address by [ exception = (addr + 1530) / 6 ].
+ *  The sole purpose of the routine _catchException is to compute the
+ *  exception number and push it on the stack in place of the return address.
+ *  The external function exceptionHandler() is
+ *  used to attach a specific handler to a specific m68k exception.
+ *  For 68020 machines, the ability to have a return address around just
+ *  so the vector can be determined is not necessary because the '020 pushes an
+ *  extra word onto the stack containing the vector offset
+ * 
+ *  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 <stdio.h>
+#include <string.h>
+#include <setjmp.h>
+
+/************************************************************************
+ *
+ * external low-level support routines 
+ */
+typedef void (*ExceptionHook)(int);   /* pointer to function with int parm */
+typedef void (*Function)();           /* pointer to a function */
+
+extern void putDebugChar();	/* write a single character      */
+extern int getDebugChar();	/* read and return a single char */
+
+extern Function exceptionHandler();  /* assign an exception handler */
+extern ExceptionHook exceptionHook;  /* hook variable for errors/exceptions */
+
+/************************/
+/* FORWARD DECLARATIONS */
+/************************/
+static void
+initializeRemcomErrorFrame ();
+
+/************************************************************************/
+/* BUFMAX defines the maximum number of characters in inbound/outbound buffers*/
+/* at least NUMREGBYTES*2 are needed for register packets */
+#define BUFMAX 400
+
+static char initialized;  /* boolean flag. != 0 means we've been initialized */
+
+int     remote_debug;
+/*  debug >  0 prints ill-formed commands in valid packets & checksum errors */ 
+
+static const char hexchars[]="0123456789abcdef";
+
+/* there are 180 bytes of registers on a 68020 w/68881      */
+/* many of the fpa registers are 12 byte (96 bit) registers */
+#define NUMREGBYTES 180
+enum regnames {D0,D1,D2,D3,D4,D5,D6,D7, 
+               A0,A1,A2,A3,A4,A5,A6,A7, 
+               PS,PC,
+               FP0,FP1,FP2,FP3,FP4,FP5,FP6,FP7,
+               FPCONTROL,FPSTATUS,FPIADDR
+              };
+
+
+/* We keep a whole frame cache here.  "Why?", I hear you cry, "doesn't
+   GDB handle that sort of thing?"  Well, yes, I believe the only
+   reason for this cache is to save and restore floating point state
+   (fsave/frestore).  A cleaner way to do this would be to make the
+ fsave data part of the registers which GDB deals with like any
+   other registers.  This should not be a performance problem if the
+   ability to read individual registers is added to the protocol.  */
+
+typedef struct FrameStruct
+{
+    struct FrameStruct  *previous;
+    int       exceptionPC;      /* pc value when this frame created */
+    int       exceptionVector;  /* cpu vector causing exception     */
+    short     frameSize;        /* size of cpu frame in words       */
+    short     sr;               /* for 68000, this not always sr    */
+    int       pc;
+    short     format;
+    int       fsaveHeader;
+    int       morejunk[0];        /* exception frame, fp save... */
+} Frame;
+
+#define FRAMESIZE 500
+int   gdbFrameStack[FRAMESIZE];
+static Frame *lastFrame;
+
+/*
+ * these should not be static cuz they can be used outside this module
+ */
+int registers[NUMREGBYTES/4];
+int superStack;
+
+#define STACKSIZE 10000
+int remcomStack[STACKSIZE/sizeof(int)];
+static int* stackPtr = &remcomStack[STACKSIZE/sizeof(int) - 1];
+
+/*
+ * In many cases, the system will want to continue exception processing
+ * when a continue command is given.  
+ * oldExceptionHook is a function to invoke in this case.
+ */
+
+static ExceptionHook oldExceptionHook;
+
+#ifdef mc68020
+/* the size of the exception stack on the 68020 varies with the type of
+ * exception.  The following table is the number of WORDS used
+ * for each exception format.
+ */
+const short exceptionSize[] = { 4,4,6,4,4,4,4,4,29,10,16,46,12,4,4,4 };
+#endif
+
+#ifdef mc68332
+static const short exceptionSize[] = { 4,4,6,4,4,4,4,4,4,4,4,4,16,4,4,4 };
+#endif
+
+/************* jump buffer used for setjmp/longjmp **************************/
+jmp_buf remcomEnv;
+
+/***************************  ASSEMBLY CODE MACROS *************************/
+/* 									   */
+
+#ifdef __HAVE_68881__
+/* do an fsave, then remember the address to begin a restore from */
+#define SAVE_FP_REGS()    asm(" fsave   a0@-");		\
+			  asm(" fmovemx fp0-fp7,_registers+72");        \
+			  asm(" fmoveml fpcr/fpsr/fpi,_registers+168"); 
+#define RESTORE_FP_REGS()                              \
+asm("                                                \n\
+    fmoveml  _registers+168,fpcr/fpsr/fpi            \n\
+    fmovemx  _registers+72,fp0-fp7                   \n\
+    cmpl     #-1,a0@     |  skip frestore flag set ? \n\
+    beq      skip_frestore                           \n\
+    frestore a0@+                                    \n\
+skip_frestore:                                       \n\
+");
+
+#else
+#define SAVE_FP_REGS()
+#define RESTORE_FP_REGS()
+#endif /* __HAVE_68881__ */
+
+void return_to_super();
+void return_to_user();
+
+asm("
+.text
+.globl _return_to_super
+_return_to_super:
+        movel   _registers+60,sp /* get new stack pointer */        
+        movel   _lastFrame,a0   /* get last frame info  */              
+        bra     return_to_any
+
+.globl _return_to_user
+_return_to_user:
+        movel   _registers+60,a0 /* get usp */                          
+        movel   a0,usp           /* set usp */				
+        movel   _superStack,sp  /* get original stack pointer */        
+
+return_to_any:
+        movel   _lastFrame,a0   /* get last frame info  */              
+        movel   a0@+,_lastFrame /* link in previous frame     */        
+        addql   #8,a0           /* skip over pc, vector#*/              
+        movew   a0@+,d0         /* get # of words in cpu frame */       
+        addw    d0,a0           /* point to end of data        */       
+        addw    d0,a0           /* point to end of data        */       
+        movel   a0,a1                                                   
+#                                                                       
+# copy the stack frame                                                  
+        subql   #1,d0                                                   
+copyUserLoop:                                                               
+        movew   a1@-,sp@-                                               
+        dbf     d0,copyUserLoop                                             
+");                                                                     
+        RESTORE_FP_REGS()                                              
+   asm("   moveml  _registers,d0-d7/a0-a6");			        
+   asm("   rte");  /* pop and go! */                                    
+
+#define DISABLE_INTERRUPTS()   asm("         oriw   #0x0700,sr");
+#define BREAKPOINT() asm("   trap #1");
+
+/* this function is called immediately when a level 7 interrupt occurs */
+/* if the previous interrupt level was 7 then we're already servicing  */
+/* this interrupt and an rte is in order to return to the debugger.    */
+/* For the 68000, the offset for sr is 6 due to the jsr return address */
+asm("
+.text
+.globl __debug_level7
+__debug_level7:
+	movew   d0,sp@-");
+#if defined (mc68020) || defined (mc68332)
+asm("	movew   sp@(2),d0");
+#else
+asm("	movew   sp@(6),d0");
+#endif
+asm("	andiw   #0x700,d0
+	cmpiw   #0x700,d0
+	beq     _already7
+        movew   sp@+,d0	
+        bra     __catchException
+_already7:
+	movew   sp@+,d0");
+#if !defined (mc68020) && !defined (mc68332)
+asm("	lea     sp@(4),sp");     /* pull off 68000 return address */
+#endif
+asm("	rte");
+
+extern void _catchException ();
+
+#if defined (mc68020) || defined (mc68332)
+/* This function is called when a 68020 exception occurs.  It saves
+ * all the cpu and fpcp regs in the _registers array, creates a frame on a
+ * linked list of frames which has the cpu and fpcp stack frames needed
+ * to properly restore the context of these processors, and invokes
+ * an exception handler (remcom_handler).
+ *
+ * stack on entry:                       stack on exit:
+ *   N bytes of junk                     exception # MSWord
+ *   Exception Format Word               exception # MSWord
+ *   Program counter LSWord              
+ *   Program counter MSWord             
+ *   Status Register                    
+ *                                       
+ *                                       
+ */
+asm(" 
+.text
+.globl __catchException
+__catchException:");
+DISABLE_INTERRUPTS();
+asm("
+        moveml  d0-d7/a0-a6,_registers /* save registers        */
+	movel	_lastFrame,a0	/* last frame pointer */
+");
+SAVE_FP_REGS();        
+asm("
+	lea     _registers,a5   /* get address of registers     */
+        movew   sp@,d1          /* get status register          */
+        movew   d1,a5@(66)      /* save sr		 	*/	
+	movel   sp@(2),a4       /* save pc in a4 for later use  */
+        movel   a4,a5@(68)      /* save pc in _regisers[]      	*/
+
+#
+# figure out how many bytes in the stack frame
+	movew   sp@(6),d0	/* get '020 exception format	*/
+        movew   d0,d2           /* make a copy of format word   */
+        andiw   #0xf000,d0      /* mask off format type         */
+        rolw    #5,d0           /* rotate into the low byte *2  */
+        lea     _exceptionSize,a1   
+        addw    d0,a1           /* index into the table         */
+	movew   a1@,d0          /* get number of words in frame */
+        movew   d0,d3           /* save it                      */
+        subw    d0,a0		/* adjust save pointer          */
+        subw    d0,a0		/* adjust save pointer(bytes)   */
+	movel   a0,a1           /* copy save pointer            */
+	subql   #1,d0           /* predecrement loop counter    */
+#
+# copy the frame
+saveFrameLoop:
+	movew  	sp@+,a1@+
+	dbf     d0,saveFrameLoop
+#
+# now that the stack has been clenaed,
+# save the a7 in use at time of exception
+        movel   sp,_superStack  /* save supervisor sp           */
+        andiw   #0x2000,d1      /* were we in supervisor mode ? */
+        beq     userMode       
+        movel   a7,a5@(60)      /* save a7                  */
+        bra     a7saveDone
+userMode:  
+	movel   usp,a1    	
+        movel   a1,a5@(60)      /* save user stack pointer	*/
+a7saveDone:
+
+#
+# save size of frame
+        movew   d3,a0@-
+
+#
+# compute exception number
+	andl    #0xfff,d2   	/* mask off vector offset	*/
+	lsrw    #2,d2   	/* divide by 4 to get vect num	*/
+        movel   d2,a0@-         /* save it                      */
+#
+# save pc causing exception
+        movel   a4,a0@-
+#
+# save old frame link and set the new value
+	movel	_lastFrame,a1	/* last frame pointer */
+	movel   a1,a0@-		/* save pointer to prev frame	*/
+        movel   a0,_lastFrame
+
+        movel   d2,sp@-		/* push exception num           */
+	movel   _exceptionHook,a0  /* get address of handler */
+        jbsr    a0@             /* and call it */
+        clrl    sp@             /* replace exception num parm with frame ptr */
+        jbsr     __returnFromException   /* jbsr, but never returns */
+");
+#else /* mc68000 */
+/* This function is called when an exception occurs.  It translates the
+ * return address found on the stack into an exception vector # which
+ * is then handled by either handle_exception or a system handler.
+ * _catchException provides a front end for both.  
+ *
+ * stack on entry:                       stack on exit:
+ *   Program counter MSWord              exception # MSWord 
+ *   Program counter LSWord              exception # MSWord
+ *   Status Register                     
+ *   Return Address  MSWord              
+ *   Return Address  LSWord             
+ */
+asm("
+.text
+.globl __catchException
+__catchException:");
+DISABLE_INTERRUPTS();
+asm("
+        moveml d0-d7/a0-a6,_registers  /* save registers               */
+	movel	_lastFrame,a0	/* last frame pointer */
+");
+SAVE_FP_REGS();        
+asm("
+        lea     _registers,a5   /* get address of registers     */
+        movel   sp@+,d2         /* pop return address           */
+	addl 	#1530,d2        /* convert return addr to 	*/
+	divs 	#6,d2   	/*  exception number		*/
+	extl    d2   
+
+        moveql  #3,d3           /* assume a three word frame     */
+
+        cmpiw   #3,d2           /* bus error or address error ? */
+        bgt     normal          /* if >3 then normal error      */
+        movel   sp@+,a0@-       /* copy error info to frame buff*/
+        movel   sp@+,a0@-       /* these are never used         */
+        moveql  #7,d3           /* this is a 7 word frame       */
+     
+normal:   
+	movew   sp@+,d1         /* pop status register          */
+        movel   sp@+,a4         /* pop program counter          */
+        movew   d1,a5@(66)      /* save sr		 	*/	
+        movel   a4,a5@(68)      /* save pc in _regisers[]      	*/
+        movel   a4,a0@-         /* copy pc to frame buffer      */
+	movew   d1,a0@-         /* copy sr to frame buffer      */
+
+        movel   sp,_superStack  /* save supervisor sp          */
+
+        andiw   #0x2000,d1      /* were we in supervisor mode ? */
+        beq     userMode       
+        movel   a7,a5@(60)      /* save a7                  */
+        bra     saveDone             
+userMode:
+        movel   usp,a1    	/* save user stack pointer 	*/
+        movel   a1,a5@(60)      /* save user stack pointer	*/
+saveDone:
+
+        movew   d3,a0@-         /* push frame size in words     */
+        movel   d2,a0@-         /* push vector number           */
+        movel   a4,a0@-         /* push exception pc            */
+
+#
+# save old frame link and set the new value
+	movel	_lastFrame,a1	/* last frame pointer */
+	movel   a1,a0@-		/* save pointer to prev frame	*/
+        movel   a0,_lastFrame
+
+        movel   d2,sp@-		/* push exception num           */
+	movel   _exceptionHook,a0  /* get address of handler */
+        jbsr    a0@             /* and call it */
+        clrl    sp@             /* replace exception num parm with frame ptr */
+        jbsr     __returnFromException   /* jbsr, but never returns */
+");
+#endif
+
+
+/*
+ * remcomHandler is a front end for handle_exception.  It moves the
+ * stack pointer into an area reserved for debugger use in case the
+ * breakpoint happened in supervisor mode.
+ */
+asm("_remcomHandler:");
+asm("           addl    #4,sp");        /* pop off return address     */
+asm("           movel   sp@+,d0");      /* get the exception number   */
+asm("		movel   _stackPtr,sp"); /* move to remcom stack area  */
+asm("		movel   d0,sp@-");	/* push exception onto stack  */
+asm("		jbsr    _handle_exception");    /* this never returns */
+asm("           rts");                  /* return */
+
+void
+_returnFromException (Frame * frame)
+{
+  /* if no passed in frame, use the last one */
+  if (!frame)
+    {
+      frame = lastFrame;
+      frame->frameSize = 4;
+      frame->format = 0;
+      frame->fsaveHeader = -1;	/* restore regs, but we dont have fsave info */
+    }
+
+#if !defined (mc68020) && !defined (mc68332)
+  /* a 68000 cannot use the internal info pushed onto a bus error
+   * or address error frame when doing an RTE so don't put this info
+   * onto the stack or the stack will creep every time this happens.
+   */
+  frame->frameSize = 3;
+#endif
+
+  /* throw away any frames in the list after this frame */
+  lastFrame = frame;
+
+  frame->sr = registers[(int) PS];
+  frame->pc = registers[(int) PC];
+
+  if (registers[(int) PS] & 0x2000)
+    {
+      /* return to supervisor mode... */
+      return_to_super ();
+    }
+  else
+    {				/* return to user mode */
+      return_to_user ();
+    }
+}
+
+int
+hex (ch)
+     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);
+}
+
+static char remcomInBuffer[BUFMAX];
+static char remcomOutBuffer[BUFMAX];
+
+/* scan for the sequence $<data>#<checksum>     */
+
+unsigned char *
+getpacket (void)
+{
+  unsigned char *buffer = &remcomInBuffer[0];
+  unsigned char checksum;
+  unsigned char xmitcsum;
+  int count;
+  char ch;
+
+  while (1)
+    {
+      /* wait around for the start character, ignore all other characters */
+      while ((ch = getDebugChar ()) != '$')
+	;
+
+    retry:
+      checksum = 0;
+      xmitcsum = -1;
+      count = 0;
+
+      /* now, read until a # or end of buffer is found */
+      while (count < BUFMAX - 1)
+	{
+	  ch = getDebugChar ();
+	  if (ch == '$')
+	    goto retry;
+	  if (ch == '#')
+	    break;
+	  checksum = checksum + ch;
+	  buffer[count] = ch;
+	  count = count + 1;
+	}
+      buffer[count] = 0;
+
+      if (ch == '#')
+	{
+	  ch = getDebugChar ();
+	  xmitcsum = hex (ch) << 4;
+	  ch = getDebugChar ();
+	  xmitcsum += hex (ch);
+
+	  if (checksum != xmitcsum)
+	    {
+	      if (remote_debug)
+		{
+		  fprintf (stderr,
+			   "bad checksum.  My count = 0x%x, sent=0x%x. buf=%s\n",
+			   checksum, xmitcsum, buffer);
+		}
+	      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]);
+
+		  return &buffer[3];
+		}
+
+	      return &buffer[0];
+	    }
+	}
+    }
+}
+
+/* send the packet in buffer. */
+
+void
+putpacket (buffer)
+     char *buffer;
+{
+  unsigned char checksum;
+  int count;
+  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 % 16]);
+
+    }
+  while (getDebugChar () != '+');
+
+}
+
+void
+debug_error (format, parm)
+     char *format;
+     char *parm;
+{
+  if (remote_debug)
+    fprintf (stderr, format, parm);
+}
+
+/* convert the memory pointed to by mem into hex, placing result in buf */
+/* return a pointer to the last char put in buf (null) */
+char *
+mem2hex (mem, buf, count)
+     char *mem;
+     char *buf;
+     int count;
+{
+  int i;
+  unsigned char ch;
+  for (i = 0; i < count; i++)
+    {
+      ch = *mem++;
+      *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 */
+char *
+hex2mem (buf, mem, count)
+     char *buf;
+     char *mem;
+     int count;
+{
+  int i;
+  unsigned char ch;
+  for (i = 0; i < count; i++)
+    {
+      ch = hex (*buf++) << 4;
+      ch = ch + hex (*buf++);
+      *mem++ = ch;
+    }
+  return (mem);
+}
+
+/* a bus error has occurred, perform a longjmp
+   to return execution and allow handling of the error */
+
+void
+handle_buserror ()
+{
+  longjmp (remcomEnv, 1);
+}
+
+/* this function takes the 68000 exception number and attempts to 
+   translate this number into a unix compatible signal value */
+int
+computeSignal (exceptionVector)
+     int exceptionVector;
+{
+  int sigval;
+  switch (exceptionVector)
+    {
+    case 2:
+      sigval = 10;
+      break;			/* bus error           */
+    case 3:
+      sigval = 10;
+      break;			/* address error       */
+    case 4:
+      sigval = 4;
+      break;			/* illegal instruction */
+    case 5:
+      sigval = 8;
+      break;			/* zero divide         */
+    case 6:
+      sigval = 8;
+      break;			/* chk instruction     */
+    case 7:
+      sigval = 8;
+      break;			/* trapv instruction   */
+    case 8:
+      sigval = 11;
+      break;			/* privilege violation */
+    case 9:
+      sigval = 5;
+      break;			/* trace trap          */
+    case 10:
+      sigval = 4;
+      break;			/* line 1010 emulator  */
+    case 11:
+      sigval = 4;
+      break;			/* line 1111 emulator  */
+
+      /* Coprocessor protocol violation.  Using a standard MMU or FPU
+         this cannot be triggered by software.  Call it a SIGBUS.  */
+    case 13:
+      sigval = 10;
+      break;
+
+    case 31:
+      sigval = 2;
+      break;			/* interrupt           */
+    case 33:
+      sigval = 5;
+      break;			/* breakpoint          */
+
+      /* This is a trap #8 instruction.  Apparently it is someone's software
+         convention for some sort of SIGFPE condition.  Whose?  How many
+         people are being screwed by having this code the way it is?
+         Is there a clean solution?  */
+    case 40:
+      sigval = 8;
+      break;			/* floating point err  */
+
+    case 48:
+      sigval = 8;
+      break;			/* floating point err  */
+    case 49:
+      sigval = 8;
+      break;			/* floating point err  */
+    case 50:
+      sigval = 8;
+      break;			/* zero divide         */
+    case 51:
+      sigval = 8;
+      break;			/* underflow           */
+    case 52:
+      sigval = 8;
+      break;			/* operand error       */
+    case 53:
+      sigval = 8;
+      break;			/* overflow            */
+    case 54:
+      sigval = 8;
+      break;			/* NAN                 */
+    default:
+      sigval = 7;		/* "software generated" */
+    }
+  return (sigval);
+}
+
+/**********************************************/
+/* WHILE WE FIND NICE HEX CHARS, BUILD AN INT */
+/* RETURN NUMBER OF CHARS PROCESSED           */
+/**********************************************/
+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);
+}
+
+/*
+ * This function does all command procesing for interfacing to gdb.
+ */
+void
+handle_exception (int exceptionVector)
+{
+  int sigval, stepping;
+  int addr, length;
+  char *ptr;
+  int newPC;
+  Frame *frame;
+
+  if (remote_debug)
+    printf ("vector=%d, sr=0x%x, pc=0x%x\n",
+	    exceptionVector, registers[PS], registers[PC]);
+
+  /* reply to host that an exception has occurred */
+  sigval = computeSignal (exceptionVector);
+  remcomOutBuffer[0] = 'S';
+  remcomOutBuffer[1] = hexchars[sigval >> 4];
+  remcomOutBuffer[2] = hexchars[sigval % 16];
+  remcomOutBuffer[3] = 0;
+
+  putpacket (remcomOutBuffer);
+
+  stepping = 0;
+
+  while (1 == 1)
+    {
+      remcomOutBuffer[0] = 0;
+      ptr = getpacket ();
+      switch (*ptr++)
+	{
+	case '?':
+	  remcomOutBuffer[0] = 'S';
+	  remcomOutBuffer[1] = hexchars[sigval >> 4];
+	  remcomOutBuffer[2] = hexchars[sigval % 16];
+	  remcomOutBuffer[3] = 0;
+	  break;
+	case 'd':
+	  remote_debug = !(remote_debug);	/* toggle debug flag */
+	  break;
+	case 'g':		/* return the value of the CPU registers */
+	  mem2hex ((char *) registers, remcomOutBuffer, NUMREGBYTES);
+	  break;
+	case 'G':		/* set the value of the CPU registers - return OK */
+	  hex2mem (ptr, (char *) registers, NUMREGBYTES);
+	  strcpy (remcomOutBuffer, "OK");
+	  break;
+
+	  /* mAA..AA,LLLL  Read LLLL bytes at address AA..AA */
+	case 'm':
+	  if (setjmp (remcomEnv) == 0)
+	    {
+	      exceptionHandler (2, handle_buserror);
+
+	      /* TRY TO READ %x,%x.  IF SUCCEED, SET PTR = 0 */
+	      if (hexToInt (&ptr, &addr))
+		if (*(ptr++) == ',')
+		  if (hexToInt (&ptr, &length))
+		    {
+		      ptr = 0;
+		      mem2hex ((char *) addr, remcomOutBuffer, length);
+		    }
+
+	      if (ptr)
+		{
+		  strcpy (remcomOutBuffer, "E01");
+		}
+	    }
+	  else
+	    {
+	      exceptionHandler (2, _catchException);
+	      strcpy (remcomOutBuffer, "E03");
+	      debug_error ("bus error");
+	    }
+
+	  /* restore handler for bus error */
+	  exceptionHandler (2, _catchException);
+	  break;
+
+	  /* MAA..AA,LLLL: Write LLLL bytes at address AA.AA return OK */
+	case 'M':
+	  if (setjmp (remcomEnv) == 0)
+	    {
+	      exceptionHandler (2, handle_buserror);
+
+	      /* TRY TO READ '%x,%x:'.  IF SUCCEED, SET PTR = 0 */
+	      if (hexToInt (&ptr, &addr))
+		if (*(ptr++) == ',')
+		  if (hexToInt (&ptr, &length))
+		    if (*(ptr++) == ':')
+		      {
+			hex2mem (ptr, (char *) addr, length);
+			ptr = 0;
+			strcpy (remcomOutBuffer, "OK");
+		      }
+	      if (ptr)
+		{
+		  strcpy (remcomOutBuffer, "E02");
+		}
+	    }
+	  else
+	    {
+	      exceptionHandler (2, _catchException);
+	      strcpy (remcomOutBuffer, "E03");
+	      debug_error ("bus error");
+	    }
+
+	  /* restore handler for bus error */
+	  exceptionHandler (2, _catchException);
+	  break;
+
+	  /* cAA..AA    Continue at address AA..AA(optional) */
+	  /* sAA..AA   Step one instruction from AA..AA(optional) */
+	case 's':
+	  stepping = 1;
+	case 'c':
+	  /* try to read optional parameter, pc unchanged if no parm */
+	  if (hexToInt (&ptr, &addr))
+	    registers[PC] = addr;
+
+	  newPC = registers[PC];
+
+	  /* clear the trace bit */
+	  registers[PS] &= 0x7fff;
+
+	  /* set the trace bit if we're stepping */
+	  if (stepping)
+	    registers[PS] |= 0x8000;
+
+	  /*
+	   * look for newPC in the linked list of exception frames.
+	   * if it is found, use the old frame it.  otherwise,
+	   * fake up a dummy frame in returnFromException().
+	   */
+	  if (remote_debug)
+	    printf ("new pc = 0x%x\n", newPC);
+	  frame = lastFrame;
+	  while (frame)
+	    {
+	      if (remote_debug)
+		printf ("frame at 0x%x has pc=0x%x, except#=%d\n",
+			frame, frame->exceptionPC, frame->exceptionVector);
+	      if (frame->exceptionPC == newPC)
+		break;		/* bingo! a match */
+	      /*
+	       * for a breakpoint instruction, the saved pc may
+	       * be off by two due to re-executing the instruction
+	       * replaced by the trap instruction.  Check for this.
+	       */
+	      if ((frame->exceptionVector == 33) &&
+		  (frame->exceptionPC == (newPC + 2)))
+		break;
+	      if (frame == frame->previous)
+		{
+		  frame = 0;	/* no match found */
+		  break;
+		}
+	      frame = frame->previous;
+	    }
+
+	  /*
+	   * If we found a match for the PC AND we are not returning
+	   * as a result of a breakpoint (33),
+	   * trace exception (9), nmi (31), jmp to
+	   * the old exception handler as if this code never ran.
+	   */
+	  if (frame)
+	    {
+	      if ((frame->exceptionVector != 9) &&
+		  (frame->exceptionVector != 31) &&
+		  (frame->exceptionVector != 33))
+		{
+		  /*
+		   * invoke the previous handler.
+		   */
+		  if (oldExceptionHook)
+		    (*oldExceptionHook) (frame->exceptionVector);
+		  newPC = registers[PC];	/* pc may have changed  */
+		  if (newPC != frame->exceptionPC)
+		    {
+		      if (remote_debug)
+			printf ("frame at 0x%x has pc=0x%x, except#=%d\n",
+				frame, frame->exceptionPC,
+				frame->exceptionVector);
+		      /* re-use the last frame, we're skipping it (longjump?) */
+		      frame = (Frame *) 0;
+		      _returnFromException (frame);	/* this is a jump */
+		    }
+		}
+	    }
+
+	  /* if we couldn't find a frame, create one */
+	  if (frame == 0)
+	    {
+	      frame = lastFrame - 1;
+
+	      /* by using a bunch of print commands with breakpoints,
+	         it's possible for the frame stack to creep down.  If it creeps
+	         too far, give up and reset it to the top.  Normal use should
+	         not see this happen.
+	       */
+	      if ((unsigned int) (frame - 2) < (unsigned int) &gdbFrameStack)
+		{
+		  initializeRemcomErrorFrame ();
+		  frame = lastFrame;
+		}
+	      frame->previous = lastFrame;
+	      lastFrame = frame;
+	      frame = 0;	/* null so _return... will properly initialize it */
+	    }
+
+	  _returnFromException (frame);	/* this is a jump */
+
+	  break;
+
+	  /* kill the program */
+	case 'k':		/* do nothing */
+	  break;
+	}			/* switch */
+
+      /* reply to the request */
+      putpacket (remcomOutBuffer);
+    }
+}
+
+
+void
+initializeRemcomErrorFrame (void)
+{
+  lastFrame = ((Frame *) & gdbFrameStack[FRAMESIZE - 1]) - 1;
+  lastFrame->previous = lastFrame;
+}
+
+/* this function is used to set up exception handlers for tracing and 
+   breakpoints */
+void
+set_debug_traps ()
+{
+  extern void _debug_level7 ();
+  extern void remcomHandler ();
+  int exception;
+
+  initializeRemcomErrorFrame ();
+  stackPtr = &remcomStack[STACKSIZE / sizeof (int) - 1];
+
+  for (exception = 2; exception <= 23; exception++)
+    exceptionHandler (exception, _catchException);
+
+  /* level 7 interrupt              */
+  exceptionHandler (31, _debug_level7);
+
+  /* breakpoint exception (trap #1) */
+  exceptionHandler (33, _catchException);
+
+  /* This is a trap #8 instruction.  Apparently it is someone's software
+     convention for some sort of SIGFPE condition.  Whose?  How many
+     people are being screwed by having this code the way it is?
+     Is there a clean solution?  */
+  exceptionHandler (40, _catchException);
+
+  /* 48 to 54 are floating point coprocessor errors */
+  for (exception = 48; exception <= 54; exception++)
+    exceptionHandler (exception, _catchException);
+
+  if (oldExceptionHook != remcomHandler)
+    {
+      oldExceptionHook = exceptionHook;
+      exceptionHook = remcomHandler;
+    }
+
+  initialized = 1;
+
+}
+
+/* This function will generate a breakpoint exception.  It is used at the
+   beginning of a program to sync up with a debugger and can be used
+   otherwise as a quick means to stop program execution and "break" into
+   the debugger. */
+
+void
+breakpoint ()
+{
+  if (initialized)
+    BREAKPOINT ();
+}