Hello,
please find enclosed the source code to differentiate 
reads from writes.....

THE PAGE FAULT HANDLER ------------------------------------------------

segv_handler(int sig, siginfo_t *sip, ucontext_t *uc)
{
...
     unsigned long pc, *pcptr;
...
     pc = (unsigned long) uc->uc_mcontext.gregs[1];
     pcptr = (unsigned long *) pc;
     instruction = *pcptr; 

...

     write_fault = STORE_INSTRUCTION(instruction);
     read_fault  = LOAD_INSTRUCTION(instruction);

     ASSERT(! (write_fault && read_fault));
     ASSERT(write_fault || read_fault);
...
}

INSTRUCTION DECODING ---------------------------------------------------
(LIFTED FROM QUARKS PROJECT AT RIVERSIDE)

-- start of .H

#ifndef SOLARIS 
THIS FILE IS ONLY FOR SPARC INSTRUCTION SET
#endif

#define op1_mask   0xC0000000
#define op2_mask   0x01F80000
#define op1_shift  24
#define op2_shift  19

#define OP_WIDTH 8
#define num_load_opcodes 20
static char *ld_op_bits[num_load_opcodes] = { 
     "11000000", /* LD        */
     "11000001", /* LDUB      */
     "11000011", /* LDD       */
     "11110011", /* LDDC      */
     "11100011", /* LDDF      */
     "11100000", /* LDF       */
     "11010000", /* LDA   (p) */
     "11110000", /* LDC       */
     "11110001", /* LDCSR     */
     "11010011", /* LDDA  (p) */
     "11100001", /* LDFSR     */
     "11001001", /* LDSB      */
     "11011001", /* LDSBA (p) */
     "11001010", /* LDSH      */
     "11011010", /* LDSHA (p) */
     "11001101", /* LDSTUB    */
     "11011101", /* LDSTUBA(p)*/
     "11010001", /* LDUBA (p) */
     "11000010", /* LDUH      */
     "11010010",	/* LDUHA (p) */
};

#define num_store_opcodes 16
static char *st_op_bits[num_store_opcodes] = {
     "11000100", /* ST        */
     "11010100", /* STA   (p) */
     "11000101", /* STB       */
     "11010101", /* STBA  (p) */
     "11110100", /* STC       */
     "11110101", /* STCR      */
     "11000111", /* STD       */
     "11010111", /* STDA  (p) */
     "11110111", /* STDC      */
     "11110110", /* STDCQ (p) */
     "11100111", /* STDF      */
     "11100110", /* STDFQ (p) */
     "11100100", /* STF       */
     "11100101", /* STFSR     */
     "10000110", /* STH       */
     "11010110", /* STHA  (p) */
};

---- END OF .H

#ifndef SOLARIS
THIS FILE IS ONLY FOR SPARC INSTRUCTION SET
#endif

static unsigned short *load_opcodes = 0;
static unsigned short *store_opcodes = 0;

static void init_opcodes()
{
     int i,j,factor,sum;

     load_opcodes  = (unsigned short *) 
	malloc(sizeof(unsigned short)*num_load_opcodes);
     store_opcodes = (unsigned short *) 
	malloc(sizeof(unsigned short)*num_store_opcodes);

     for (i=0; i<num_load_opcodes; i++)
     {	
	factor = 1;
	sum = 0;
	for (j = OP_WIDTH-1; j >= 0; j--)
	{
	    sum += factor * ((ld_op_bits[i][j] == '1') ? 1 : 0);
	    factor = factor << 1;
	}
	load_opcodes[i] = sum;
     }
     for (i=0; i<num_store_opcodes; i++)
     {	
	factor = 1;
	sum = 0;
	for (j = OP_WIDTH-1; j >= 0; j--)
	{
	    sum += factor * ((st_op_bits[i][j] == '1') ? 1 : 0);
	    factor = factor << 1;
	}
	store_opcodes[i] = sum;
     }
}

int LOAD_INSTRUCTION(unsigned long inst)
{
     int i;

     unsigned long opcode =  ((inst & op1_mask) >> op1_shift) |
	                    ((inst & op2_mask) >> op2_shift);
     
     if (! load_opcodes) init_opcodes();

     for (i=0; i<num_load_opcodes; i++)
     {
	if (opcode == load_opcodes[i])
	{
	    return 1;
	}
     }
     return 0;
}

int STORE_INSTRUCTION(unsigned long inst)
{
     int i;

     unsigned short opcode = (unsigned short) 
	                    ((inst & op1_mask) >> op1_shift) |
	                    ((inst & op2_mask) >> op2_shift);
     
     if (! store_opcodes) init_opcodes();

     for (i=0; i<num_store_opcodes; i++)
     {
	if (opcode == store_opcodes[i])
	{
	    return 1;
	}
     }
     return 0;
}