m68k-stub.c

RTEMS (Real-Time Executive for Multiprocessor Systems) is a free open source real-time operating sys

#define  GDB_STUB_ENABLE_THREAD_SUPPORT 1
/****************************************************************************

		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
 * 
 ***************************************************************************
 *    added 05/27/02 by IMD, Thomas Doerfler:
 *    XAA..AA,LLLL: Write LLLL binary bytes at address AA.AA      OK or ENN
 ****************************************************************************/

#include <stdio.h>
#include <string.h>
#include <setjmp.h>
/* #include <asm.h>*/
#include <rtems.h>
#include <rtems/score/cpu.h>
#include "gdb_if.h"

#if defined(GDB_STUB_ENABLE_THREAD_SUPPORT)
static char do_threads = 1;      /* != 0 means we are supporting threads */
int current_thread_registers[NUMREGBYTES/4];
#endif

/************************************************************************
 *
 * 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 */


/************************/
/* 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 */ 

const char gdb_hexchars[]="0123456789abcdef";
#define highhex(x) gdb_hexchars [(x >> 4) & 0xf]
#define lowhex(x) gdb_hexchars [x & 0xf]



/* 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;
/* the size of the exception stack on the 68020/30/40/CPU32 varies with 
 * the type of exception.  The following table is the number of WORDS used
 * for each exception format.
 * This table should be common for all 68k with VBR
 * although each member only implements some of the formats
 */
const short exceptionSize[] = { 4,4,6,6,4,4,4,30,29,10,16,46,12,4,4,4 };


/************* 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(" fmovem.x %fp0-%fp7,registers+72");        \
			  asm(" fmovem.l %fpcr/%fpsr/%fpi,registers+168"); 
#define RESTORE_FP_REGS()                              \
asm("                                                \n\
    fmovem.l  registers+168,%fpcr/%fpsr/%fpi            \n\
    fmovem.x  registers+72,%fp0-%fp7                   \n\
    cmp.l     #-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();
extern void _catchException ();

void m68k_exceptionHandler
(
 int vecnum,                            /* vector index to hook at         */
 void *vector                           /* address of handler function     */
)
{
  void **vec_base = NULL;
#if M68K_HAS_VBR
  /*
   * get vector base register
   */
  asm(" movec.l %%vbr,%0":"=a" (vec_base));
#endif
  vec_base[vecnum] = vector;
}

ExceptionHook exceptionHook;  /* hook variable for errors/exceptions */

void m68k_stub_dummy_asm_wrapper() 
     /*
      * this dummy wrapper function ensures, 
      * that the C compiler manages sections properly
      */
{
asm("\n\
.globl return_to_super 							\n\
return_to_super:							\n\
        move.l   registers+60,%sp /* get new stack pointer */         	\n\
        move.l   lastFrame,%a0   /* get last frame info  */           	\n\
        bra     return_to_any                                         	\n\
									\n\
.globl _return_to_user							\n\
return_to_user:								\n\
        move.l   registers+60,%a0 /* get usp */                       	\n\
        move.l   %a0,%usp           /* set usp */		  	\n\
        move.l   superStack,%sp  /* get original stack pointer */       \n\
									\n\
return_to_any: 								\n\
        move.l   lastFrame,%a0   /* get last frame info  */             \n\
        move.l   (%a0)+,lastFrame /* link in previous frame     */      \n\
        addq.l   #8,%a0           /* skip over pc, vector#*/            \n\
        move.w   (%a0)+,%d0         /* get # of words in cpu frame */   \n\
        add.w    %d0,%a0           /* point to end of data        */    \n\
        add.w    %d0,%a0           /* point to end of data        */    \n\
        move.l   %a0,%a1                                                \n\
#                                                                       \n\
# copy the stack frame                                                  \n\
        subq.l   #1,%d0                                                 \n\
copyUserLoop:                                                           \n\
        move.w   -(%a1),-(%sp) 						\n\
        dbf     %d0,copyUserLoop                                        \n\
");
        RESTORE_FP_REGS() 
   asm("   movem.l  registers,%d0-%d7/%a0-%a6");			        
   asm("   rte");  /* pop and go! */                                    

#define DISABLE_INTERRUPTS()   asm("         oriw   #0x0700,%sr");
#define BREAKPOINT() asm("   trap #2");

/* 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("						\n\
.text						\n\
.globl _debug_level7				\n\
_debug_level7:					\n\
	move.w   %d0,-(%sp)");
#if M68K_HAS_VBR
asm("	move.w   2(%sp),%d0");
#else
asm("	move.w   6(%sp),%d0");
#endif
asm("	andi.w   #0x700,%d0			\n\
	cmpi.w   #0x700,%d0			\n\
	beq     already7			\n\
        move.w   (%sp)+,%d0			\n\
        bra     _catchException			\n\
already7:					\n\
	move.w   (%sp)+,%d0");
#if !M68K_HAS_VBR
asm("	lea     4(%sp),%sp");     /* pull off 68000 return address */
#endif
asm("	rte");


#if M68K_HAS_VBR
/* 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(" 						\n\
.text						\n\
.globl _catchException				\n\
_catchException:");
DISABLE_INTERRUPTS();
asm("									\n\
        movem.l  %d0-%d7/%a0-%a6,registers /* save registers        */	\n\
	move.l	lastFrame,%a0	/* last frame pointer */		\n\
");
SAVE_FP_REGS();        
asm("\n\
	lea     registers,%a5   /* get address of registers     */\n\
        move.w  (%sp),%d1        /* get status register          */\n\
        move.w   %d1,66(%a5)      /* save sr		 	*/	\n\
	move.l   2(%sp),%a4      /* save pc in a4 for later use  */\n\
	move.w   6(%sp),%d0	/* get '020 exception format	*/\n\
        move.w   %d0,%d2        /* make a copy of format word   */\n\
#\n\
# compute exception number\n\
	and.l    #0xfff,%d2   	/* mask off vector offset	*/\n\
	lsr.w    #2,%d2   	/* divide by 4 to get vect num	*/\n\
/* #if 1 */\n\
        cmp.l    #33,%d2\n\
        bne      nopc_adjust\n\
        subq.l   #2,%a4\n\
nopc_adjust:\n\
/* #endif */\n\
        move.l   %a4,68(%a5)     /* save pc in _regisers[]      	*/\n\
\n\
#\n\
# figure out how many bytes in the stack frame\n\
        andi.w   #0xf000,%d0    /* mask off format type         */\n\
        rol.w    #5,%d0         /* rotate into the low byte *2  */\n\
        lea     exceptionSize,%a1   \n\
        add.w    %d0,%a1        /* index into the table         */\n\
	move.w   (%a1),%d0      /* get number of words in frame */\n\
        move.w   %d0,%d3        /* save it                      */\n\
        sub.w    %d0,%a0	/* adjust save pointer          */\n\
        sub.w    %d0,%a0	/* adjust save pointer(bytes)   */\n\
	move.l   %a0,%a1        /* copy save pointer            */\n\
	subq.l   #1,%d0         /* predecrement loop counter    */\n\
#\n\
# copy the frame\n\
saveFrameLoop:\n\
	move.w 	(%sp)+,(%a1)+\n\
	dbf     %d0,saveFrameLoop\n\
#\n\
# now that the stack has been clenaed,\n\
# save the a7 in use at time of exception\n\
        move.l   %sp,superStack  /* save supervisor sp           */\n\
        andi.w   #0x2000,%d1      /* were we in supervisor mode ? */\n\
        beq      userMode       \n\
        move.l   %a7,60(%a5)      /* save a7                  */\n\
        bra      a7saveDone\n\
userMode:  \n\
	move.l   %usp,%a1    	\n\
        move.l   %a1,60(%a5)      /* save user stack pointer	*/\n\
a7saveDone:\n\
\n\
#\n\
# save size of frame\n\
        move.w   %d3,-(%a0)\n\
\n\
        move.l   %d2,-(%a0)     /* save vector number           */\n\
#\n\
# save pc causing exception\n\
        move.l   %a4,-(%a0)\n\
#\n\
# save old frame link and set the new value\n\
	move.l	lastFrame,%a1	/* last frame pointer */\n\
	move.l   %a1,-(%a0)		/* save pointer to prev frame	*/\n\
        move.l   %a0,lastFrame\n\
\n\
        move.l   %d2,-(%sp)  	    /* push exception num           */\n\
	move.l   exceptionHook,%a0  /* get address of handler */\n\
        jbsr    (%a0)             /* and call it */\n\
        clr.l   (%sp)            /* replace exception num parm with frame ptr */\n\
        jbsr     _returnFromException   /* jbsr, but never returns */\n\
");
#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("\n\
.text\n\
.globl _catchException\n\