m68k-stub.c

早期freebsd实现

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

		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.
 *  
 *  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 68k 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>
#include "ansidecl.h"

/************************************************************************
 *
 * external low-level support routines 
 */
typedef void (*ExceptionHook)(int);   /* pointer to function with int parm */
typedef void (*Function)();           /* pointer to a function */

extern putDebugChar();   /* write a single character      */
extern 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 PARAMS ((void));

/************************************************************************/
/* 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
              };

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 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 };

/************* 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@-");
#ifdef mc68020
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");
#ifndef mc68020
asm("	lea     sp@(4),sp");     /* pull off 68000 return address */
#endif
asm("	rte");

extern void _catchException PARAMS ((void));

#ifdef mc68020
/* 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)   */