Beispiel #1
0
static dr_emit_flags_t
bb_event(void* drcontext, void *tag, instrlist_t *bb, bool for_trace, bool translating)
{
    instr_t *instr, *next_instr;
    int opcode;
    for (instr = instrlist_first(bb); instr != NULL; instr = next_instr) {
        next_instr = instr_get_next(instr);
        opcode = instr_get_opcode(instr);
	if(instr_is_floating(instr)){
   	//	dr_fprintf(logF, "Has seen FPU instruction with opcode %d\n",opcode);
	
	}
	else if(is_SIMD_packed(opcode)){
   	//	dr_fprintf(logF, "Has seen SIMD packed instruction with opcode %d\n",opcode);
	}
//AVX?rcpps?

	else if(is_SIMD_arithm(opcode)){
		int is_single = 0;
//		printf("opcode is   %d\n", opcode);
//    		printf("number of sources  %d\n", instr_num_srcs(instr));  
 //   		printf("number of dests  %d\n", instr_num_dsts(instr));
		//assert(number of sources = 2);
		opnd_t source1 = instr_get_src(instr,0);
		opnd_t source2 = instr_get_src(instr,1);
		opnd_t dest = instr_get_dst(instr,0);
		if(opnd_is_memory_reference(source1)){
	//		dr_print_instr(drcontext, logF, instr, "INSTR: ");
//			dr_print_opnd(drcontext, logF, source1, "OPND1: ");
//			dr_print_opnd(drcontext, logF, source2, "OPND2: ");
			reg_id_t rd = opnd_get_reg(source2);
			reg_id_t rs = opnd_get_reg_used(source1, 0);
			dr_insert_clean_call(drcontext, bb, instr, 
				(void*) callback, true, 5, 
				OPND_CREATE_INTPTR(rs), OPND_CREATE_INTPTR(opnd_get_disp(source1)),
				OPND_CREATE_INTPTR(rd), OPND_CREATE_INTPTR(opcode), OPND_CREATE_INTPTR(instr_get_app_pc(instr)));

		}
		else if(opnd_is_reg(source1) && opnd_is_reg(source2)){
			reg_id_t reg1 = opnd_get_reg(source1);
			reg_id_t reg2 = opnd_get_reg(source2);
			dr_insert_clean_call(drcontext,bb,instr, (void*)getRegReg, 
				true, 4, 
				OPND_CREATE_INTPTR(reg1), OPND_CREATE_INTPTR(reg2)
				,OPND_CREATE_INTPTR(opcode), OPND_CREATE_INTPTR(instr_get_app_pc(instr))
			); 
		}
		else{
		//should not be the case, throw an exception
		}
	        fp_count++; 
      }
    }

    return DR_EMIT_DEFAULT;
}
Beispiel #2
0
/* XXX: exporting this so drwrap can use it but I might prefer to have
 * this in drutil or the upcoming drsys
 */
DR_EXPORT
int
drmgr_decode_sysnum_from_wrapper(app_pc entry)
{
    void *drcontext = dr_get_current_drcontext();
    int num = -1;
    byte *pc = entry;
    uint opc;
    instr_t instr;
    instr_init(drcontext, &instr);
    do {
        instr_reset(drcontext, &instr);
        pc = decode(drcontext, pc, &instr);
        if (!instr_valid(&instr))
            break; /* unknown system call sequence */
        opc = instr_get_opcode(&instr);
        /* sanity check: wrapper should be short */
        if (pc - entry > 20)
            break; /* unknown system call sequence */
        if (opc == OP_mov_imm && opnd_is_reg(instr_get_dst(&instr, 0)) &&
            opnd_get_reg(instr_get_dst(&instr, 0)) == DR_REG_EAX &&
            opnd_is_immed_int(instr_get_src(&instr, 0))) {
            num = (int) opnd_get_immed_int(instr_get_src(&instr, 0));
            break; /* success */
        }
        /* stop at call to vsyscall (wow64) or at int itself */
    } while (opc != OP_call_ind && opc != OP_int &&
             opc != OP_sysenter && opc != OP_syscall);
    instr_free(drcontext, &instr);
    return num;
}
Beispiel #3
0
static inline void collect_regs(
        unsigned long *regs,
        instr_t *instr,
        int (*num_ops)(instr_t *),
        opnd_t (*get_op)(instr_t *, uint)
) {
    int i;
    opnd_t opnd;

    // make sure these regs are always seen as "used"
    *regs |= (1 << DR_REG_NULL);

    for(i=0; i < num_ops(instr); i++) {
        opnd = get_op(instr, i);
        if(opnd_is_reg(opnd)) {
            collect_reg(regs, opnd_get_reg(opnd));
        } else if(opnd_is_base_disp(opnd)) {
            collect_reg(regs, opnd_get_base(opnd));
            collect_reg(regs, opnd_get_index(opnd));
        }
    }

    collect_reg(regs, DR_REG_RSP);
    collect_reg(regs, DR_REG_RBP);
    collect_reg(regs, DR_REG_RAX);
    collect_reg(regs, DR_REG_RDX);
}
Beispiel #4
0
static dr_emit_flags_t
event_app_analysis(void *drcontext, void *tag, instrlist_t *bb,
                   bool for_trace, bool translating, OUT void **user_data)
{
    instr_t *inst, *label;
    bool prev_was_mov_const = false;
    ptr_int_t val1, val2;
    *user_data = NULL;
    /* Look for duplicate mov immediates telling us which subtest we're in */
    for (inst = instrlist_first_app(bb); inst != NULL; inst = instr_get_next_app(inst)) {
        if (instr_is_mov_constant(inst, prev_was_mov_const ? &val2 : &val1)) {
            if (prev_was_mov_const && val1 == val2 &&
                val1 != 0 && /* rule out xor w/ self */
                opnd_is_reg(instr_get_dst(inst, 0)) &&
                opnd_get_reg(instr_get_dst(inst, 0)) == TEST_REG) {
                *user_data = (void *) val1;
                label = INSTR_CREATE_label(drcontext);
                instr_set_translation(label, instr_get_app_pc(inst));
                instrlist_meta_postinsert(bb, inst, label);
            } else
                prev_was_mov_const = true;
        } else
            prev_was_mov_const = false;
    }
    return DR_EMIT_DEFAULT;
}
Beispiel #5
0
static print_base_disp_for_lea(file_t file, opnd_t opnd){

	/* [base + index * scale + disp] */
	dr_fprintf(file, " base - %d %s\n", opnd_get_base(opnd), get_register_name(opnd_get_base(opnd)));
	dr_fprintf(file, " index - %d %s\n", opnd_get_index(opnd), get_register_name(opnd_get_index(opnd)));
	dr_fprintf(file, "reg - %d\n", opnd_is_reg(opnd_create_reg(opnd_get_index(opnd))));
	dr_fprintf(file, " scale - %d\n", opnd_get_scale(opnd));
	dr_fprintf(file, " disp - %d\n", opnd_get_disp(opnd));

}
Beispiel #6
0
static uint calculate_operands(instr_t * instr,uint dst_or_src){

	opnd_t op;
	int i;
	int ret = 0;

	if(dst_or_src == DST_TYPE){
		for(i=0; i<instr_num_dsts(instr); i++){
			op = instr_get_dst(instr,i);

			if(opnd_is_immed(op) ||
				opnd_is_memory_reference(op) ||
				opnd_is_reg(op)){
				ret++;
			}
		}
	}
	else if(dst_or_src == SRC_TYPE){
		for(i=0; i<instr_num_srcs(instr); i++){
			op = instr_get_src(instr,i);

			if (instr_get_opcode(instr) == OP_lea && opnd_is_base_disp(op)){
				ret += 4;

			}
			else if (opnd_is_immed(op) ||
				opnd_is_memory_reference(op) ||
				opnd_is_reg(op)){
				ret++;
			}

		}
	}

	return ret;

}
Beispiel #7
0
static bool
instr_is_reg_restore(instr_t *instr, reg_id_t reg, umbra_info_t *info)
{
    opnd_t opnd;
    int    slot;

    if (instr_get_opcode(instr) != OP_mov_ld)
        return false;
    opnd = instr_get_dst(instr, 0);
    if (!opnd_is_reg(opnd) || opnd_get_reg(opnd) != reg)
        return false;
    slot = reg - REG_SPILL_START;
    opnd = OPND_CREATE_ABSMEM(&info->spill_regs[slot], OPSZ_PTR);
    if (opnd_same(opnd, instr_get_src(instr, 0)))
        return true;
    return false;
}
Beispiel #8
0
/* returns whether found a syscall
 * - found_eax: whether the caller has seen "mov imm => %eax"
 * - found_edx: whether the caller has seen "mov $0x7ffe0300 => %edx",
 *              xref the comment below about "mov $0x7ffe0300 => %edx".
 */
static bool
process_syscall_instr(void *dcontext, instr_t *instr, bool found_eax, bool found_edx)
{
    /* ASSUMPTION: a mov imm of 0x7ffe0300 into edx followed by an
     * indirect call via edx is a system call on XP and later
     * On XP SP1 it's call *edx, while on XP SP2 it's call *(edx)
     * For wow it's a call through fs.
     * FIXME - core exports various is_*_syscall routines (such as
     * instr_is_wow64_syscall()) which we could use here instead of
     * duplicating if they were more flexible about when they could
     * be called (instr_is_wow64_syscall() for ex. asserts if not
     * in a wow process).
     */
    if (/* int 2e or x64 or win8 sysenter */
        (instr_is_syscall(instr) &&
         found_eax && (expect_int2e || expect_x64 || expect_sysenter)) ||
        /* sysenter case */
        (expect_sysenter && found_edx && found_eax &&
         instr_is_call_indirect(instr) &&
         /* XP SP{0,1}, 2003 SP0: call *edx */
         ((opnd_is_reg(instr_get_target(instr)) &&
           opnd_get_reg(instr_get_target(instr)) == REG_EDX) ||
          /* XP SP2, 2003 SP1: call *(edx) */
          (opnd_is_base_disp(instr_get_target(instr)) &&
           opnd_get_base(instr_get_target(instr)) == REG_EDX &&
           opnd_get_index(instr_get_target(instr)) == REG_NULL &&
           opnd_get_disp(instr_get_target(instr)) == 0))) ||
        /* wow case
         * we don't require found_ecx b/c win8 does not use ecx
         */
        (expect_wow && found_eax &&
         instr_is_call_indirect(instr) &&
         ((opnd_is_far_base_disp(instr_get_target(instr)) &&
           opnd_get_base(instr_get_target(instr)) == REG_NULL &&
           opnd_get_index(instr_get_target(instr)) == REG_NULL &&
           opnd_get_segment(instr_get_target(instr)) == SEG_FS) ||
          /* win10 has imm in edx and a near call */
          found_edx)))
        return true;
    return false;
}
Beispiel #9
0
/* prints out the operands / populates the operands in the instrace mode */
static void output_populator_printer(void * drcontext, opnd_t opnd, instr_t * instr, uint64 addr, uint mem_type, operand_t * output){


	int value;
	float float_value;
	uint width;
	int i;

	per_thread_t * data = drmgr_get_tls_field(drcontext,tls_index);


	if(opnd_is_reg(opnd)){
		
		value = opnd_get_reg(opnd);
		if (value != DR_REG_NULL){
			width = opnd_size_in_bytes(reg_get_size(value));
		}
		else{
			width = 0;
		}
		
#ifdef READABLE_TRACE
		dr_fprintf(data->outfile,",%u,%u,%u",REG_TYPE, width, value);
#else	
		output->type = REG_TYPE; 
		output->width = width;
		output->value = value;

#endif
	
	}
	else if(opnd_is_immed(opnd)){
		
		//DR_ASSERT(opnd_is_immed_float(opnd) == false);

		if(opnd_is_immed_float(opnd)){

			width = opnd_size_in_bytes(opnd_get_size(opnd));

			if (instr_get_opcode(instr) == OP_fld1){
				dr_fprintf(data->outfile, ",%u,%u,1", IMM_FLOAT_TYPE, width);
			}
			else if (instr_get_opcode(instr) == OP_fldz){
				dr_fprintf(data->outfile, ",%u,%u,0", IMM_FLOAT_TYPE, width);
			}
			else{
				dr_messagebox("immediate float unknown\n");
				dr_abort();
			}

			//float_value = opnd_get_immed_float(opnd);

#ifdef READABLE_TRACE
			//dr_fprintf(data->outfile,",%u,%u,%.4f",IMM_FLOAT_TYPE,width,float_value);
#else
			output->type = IMM_FLOAT_TYPE;
			output->width = width;
			output->float_value = float_value;
#endif

		}
		
		if(opnd_is_immed_int(opnd)){

			width = opnd_size_in_bytes(opnd_get_size(opnd));
			value = opnd_get_immed_int(opnd);
#ifdef READABLE_TRACE
			dr_fprintf(data->outfile,",%u,%u,%d",IMM_INT_TYPE,width,value);
#else
			output->type = IMM_INT_TYPE;
			output->width = width;
			output->value = value;
#endif
		}

	}
	else if(opnd_is_memory_reference(opnd)){

		width = drutil_opnd_mem_size_in_bytes(opnd,instr);
#ifdef READABLE_TRACE
		dr_fprintf(data->outfile, ",%u,%u,%llu",mem_type,width,addr);
#else
		output->type = mem_type;
		output->width = width;
		output->float_value = addr;
#endif

	}
	

}
Beispiel #10
0
/* returns false on failure */
static bool
decode_syscall_num(void *dcontext, byte *entry, syscall_info_t *info, LOADED_IMAGE *img)
{
    /* FIXME: would like to fail gracefully rather than have a DR assertion
     * on non-code! => use DEBUG=0 INTERNAL=1 DR build!
     */
    bool found_syscall = false, found_eax = false, found_edx = false, found_ecx = false;
    bool found_ret = false;
    byte *pc, *pre_pc;
    int num_instr = 0;
    instr_t *instr;
    byte *preferred = get_preferred_base(img);
    if (entry == NULL)
        return false;
    info->num_args = -1; /* if find sysnum but not args */
    info->sysnum = -1;
    info->fixup_index = -1;
    instr = instr_create(dcontext);
    pc = entry;
    /* FIXME - we don't support decoding 64bit instructions in 32bit mode, but I want
     * this to work on 32bit machines.  Hack fix based on the wrapper pattern, we skip
     * the first instruction (mov r10, rcx) here, the rest should decode ok.
     * Xref PR 236203. */
    if (expect_x64 && *pc == 0x4c && *(pc+1) == 0x8b && *(pc+2) == 0xd1)
        pc += 3;
    while (true) {
        instr_reset(dcontext, instr);
        pre_pc = pc;
        pc = decode(dcontext, pc, instr);
        if (verbose) {
            instr_set_translation(instr, pre_pc);
            dr_print_instr(dcontext, STDOUT, instr, "");
        }
        if (pc == NULL || !instr_valid(instr))
            break;
        if (instr_is_syscall(instr) || instr_is_call_indirect(instr)) {
            /* If we see a syscall instr or an indirect call which is not syscall,
             * we assume this is not a syscall wrapper.
             */
            found_syscall = process_syscall_instr(dcontext, instr, found_eax, found_edx);
            if (!found_syscall)
                break; /* assume not a syscall wrapper, give up gracefully */
        } else if (instr_is_return(instr)) {
            /* we must break on return to avoid case like win8 x86
             * which has sysenter callee adjacent-"inlined"
             *     ntdll!NtYieldExecution:
             *     77d7422c b801000000  mov     eax,1
             *     77d74231 e801000000  call    ntdll!NtYieldExecution+0xb (77d74237)
             *     77d74236 c3          ret
             *     77d74237 8bd4        mov     edx,esp
             *     77d74239 0f34        sysenter
             *     77d7423b c3          ret
             */
            if (!found_ret) {
                process_ret(instr, info);
                found_ret = true;
            }
            break;
        } else if (instr_get_opcode(instr) == OP_call) {
            found_syscall = process_syscall_call(dcontext, pc, instr,
                                                 found_eax, found_edx);
            /* If we see a call and it is not a sysenter callee,
             * we assume this is not a syscall wrapper.
             */
            if (!found_syscall)
                break; /* assume not a syscall wrapper, give up gracefully */
        } else if (instr_is_cti(instr)) {
            /* We expect only ctis like ret or ret imm, syscall, and call, which are
             * handled above. Give up gracefully if we hit any other cti.
             * XXX: what about jmp to shared ret (seen in the past on some syscalls)?
             */
            /* Update: win10 TH2 1511 x64 has a cti:
             *   ntdll!NtContinue:
             *   00007ff9`13185630 4c8bd1          mov     r10,rcx
             *   00007ff9`13185633 b843000000      mov     eax,43h
             *   00007ff9`13185638 f604250803fe7f01 test    byte ptr [SharedUserData+0x308 (00000000`7ffe0308)],1
             *   00007ff9`13185640 7503            jne     ntdll!NtContinue+0x15 (00007ff9`13185645)
             *   00007ff9`13185642 0f05            syscall
             *   00007ff9`13185644 c3              ret
             *   00007ff9`13185645 cd2e            int     2Eh
             *   00007ff9`13185647 c3              ret
             */
            if (expect_x64 && instr_is_cbr(instr) &&
                opnd_get_pc(instr_get_target(instr)) == pc + 3/*syscall;ret*/) {
                /* keep going */
            } else
                break;
        } else if ((!found_eax || !found_edx || !found_ecx) &&
                   instr_get_opcode(instr) == OP_mov_imm &&
                   opnd_is_reg(instr_get_dst(instr, 0))) {
            if (!found_eax && opnd_get_reg(instr_get_dst(instr, 0)) == REG_EAX) {
                info->sysnum = (int) opnd_get_immed_int(instr_get_src(instr, 0));
                found_eax = true;
            } else if (!found_edx && opnd_get_reg(instr_get_dst(instr, 0)) == REG_EDX) {
                uint imm = (uint) opnd_get_immed_int(instr_get_src(instr, 0));
                if (imm == 0x7ffe0300 ||
                    /* On Win10 the immed is ntdll!Wow64SystemServiceCall */
                    (expect_wow && imm > (ptr_uint_t)preferred &&
                     imm < (ptr_uint_t)preferred + img->SizeOfImage))
                    found_edx = true;
            } else if (!found_ecx && opnd_get_reg(instr_get_dst(instr, 0)) == REG_ECX) {
                found_ecx = true;
                info->fixup_index = (int) opnd_get_immed_int(instr_get_src(instr, 0));
            }
        } else if (instr_get_opcode(instr) == OP_xor &&
                   opnd_is_reg(instr_get_src(instr, 0)) &&
                   opnd_get_reg(instr_get_src(instr, 0)) == REG_ECX &&
                   opnd_is_reg(instr_get_dst(instr, 0)) &&
                   opnd_get_reg(instr_get_dst(instr, 0)) == REG_ECX) {
            /* xor to 0 */
            found_ecx = true;
            info->fixup_index = 0;
        }
        num_instr++;
        if (num_instr > MAX_INSTRS_BEFORE_SYSCALL) /* wrappers should be short! */
            break; /* avoid weird cases like NPXEMULATORTABLE */
    }
    instr_destroy(dcontext, instr);
    return found_syscall;
}
Beispiel #11
0
/* returns false on failure */
static bool
decode_syscall_num(void *dcontext, byte *entry, syscall_info_t *info)
{
    /* FIXME: would like to fail gracefully rather than have a DR assertion
     * on non-code! => use DEBUG=0 INTERNAL=1 DR build!
     */
    bool found_syscall = false, found_eax = false, found_edx = false, found_ecx = false;
    bool found_ret = false;
    byte *pc;
    int num_instr = 0;
    instr_t *instr;
    if (entry == NULL)
        return false;
    info->num_args = -1; /* if find sysnum but not args */
    info->sysnum = -1;
    info->fixup_index = -1;
    instr = instr_create(dcontext);
    pc = entry;
    /* FIXME - we don't support decoding 64bit instructions in 32bit mode, but I want
     * this to work on 32bit machines.  Hack fix based on the wrapper pattern, we skip
     * the first instruction (mov r10, rcx) here, the rest should decode ok.
     * Xref PR 236203. */
    if (expect_x64 && *pc == 0x4c && *(pc+1) == 0x8b && *(pc+2) == 0xd1)
        pc += 3;
    while (true) {
        instr_reset(dcontext, instr);
        pc = decode(dcontext, pc, instr);
        if (verbose)
            dr_print_instr(dcontext, STDOUT, instr, "");
        if (pc == NULL || !instr_valid(instr))
            break;
        /* ASSUMPTION: a mov imm of 0x7ffe0300 into edx followed by an
         * indirect call via edx is a system call on XP and later
         * On XP SP1 it's call *edx, while on XP SP2 it's call *(edx)
         * For wow it's a call through fs.
         * FIXME - core exports various is_*_syscall routines (such as
         * instr_is_wow64_syscall()) which we could use here instead of
         * duplicating if they were more flexible about when they could
         * be called (instr_is_wow64_syscall() for ex. asserts if not
         * in a wow process).
         */
        if (/* int 2e or x64 or win8 sysenter */
            (instr_is_syscall(instr) && found_eax && (expect_int2e || expect_x64 || expect_sysenter)) ||
            /* sysenter case */
            (expect_sysenter && found_edx && found_eax &&
             instr_is_call_indirect(instr) &&
             /* XP SP{0,1}, 2003 SP0: call *edx */
             ((opnd_is_reg(instr_get_target(instr)) &&
               opnd_get_reg(instr_get_target(instr)) == REG_EDX) ||
              /* XP SP2, 2003 SP1: call *(edx) */
              (opnd_is_base_disp(instr_get_target(instr)) &&
               opnd_get_base(instr_get_target(instr)) == REG_EDX &&
               opnd_get_index(instr_get_target(instr)) == REG_NULL &&
               opnd_get_disp(instr_get_target(instr)) == 0))) ||
            /* wow case 
             * we don't require found_ecx b/c win8 does not use ecx
             */
            (expect_wow && found_eax &&
             instr_is_call_indirect(instr) &&
             opnd_is_far_base_disp(instr_get_target(instr)) &&
             opnd_get_base(instr_get_target(instr)) == REG_NULL &&
             opnd_get_index(instr_get_target(instr)) == REG_NULL &&
             opnd_get_segment(instr_get_target(instr)) == SEG_FS)) {
            found_syscall = true;
        } else if (instr_is_return(instr)) {
            if (!found_ret) {
                process_ret(instr, info);
                found_ret = true;
            }
            break;
        } else if (instr_is_cti(instr)) {
            if (instr_get_opcode(instr) == OP_call) {
                /* handle win8 x86 which has sysenter callee adjacent-"inlined"
                 *     ntdll!NtYieldExecution:
                 *     77d7422c b801000000      mov     eax,1
                 *     77d74231 e801000000      call    ntdll!NtYieldExecution+0xb (77d74237)
                 *     77d74236 c3              ret
                 *     77d74237 8bd4            mov     edx,esp
                 *     77d74239 0f34            sysenter
                 *     77d7423b c3              ret
                 */
                byte *tgt;
                assert(opnd_is_pc(instr_get_target(instr)));
                tgt = opnd_get_pc(instr_get_target(instr));
                /* we expect only ret or ret imm, and possibly some nops (in gdi32).
                 * XXX: what about jmp to shared ret (seen in the past on some syscalls)?
                 */
                if (tgt > pc && tgt <= pc + 16) {
                    bool ok = false;
                    do {
                        if (pc == tgt) {
                            ok = true;
                            break;
                        }
                        instr_reset(dcontext, instr);
                        pc = decode(dcontext, pc, instr);
                        if (verbose)
                            dr_print_instr(dcontext, STDOUT, instr, "");
                        if (instr_is_return(instr)) {
                            process_ret(instr, info);
                            found_ret = true;
                        } else if (!instr_is_nop(instr))
                            break;
                        num_instr++;
                    } while (num_instr <= MAX_INSTRS_BEFORE_SYSCALL);
                    if (ok)
                        continue;
                }
            }
            /* assume not a syscall wrapper if we hit a cti */
            break; /* give up gracefully */
        } else if ((!found_eax || !found_edx || !found_ecx) &&
            instr_get_opcode(instr) == OP_mov_imm &&
            opnd_is_reg(instr_get_dst(instr, 0))) {
            if (!found_eax && opnd_get_reg(instr_get_dst(instr, 0)) == REG_EAX) {
                info->sysnum = (int) opnd_get_immed_int(instr_get_src(instr, 0));
                found_eax = true;
            } else if (!found_edx && opnd_get_reg(instr_get_dst(instr, 0)) == REG_EDX) {
                int imm = (int) opnd_get_immed_int(instr_get_src(instr, 0));
                if (imm == 0x7ffe0300)
                    found_edx = true;
            } else if (!found_ecx && opnd_get_reg(instr_get_dst(instr, 0)) == REG_ECX) {
                found_ecx = true;
                info->fixup_index = (int) opnd_get_immed_int(instr_get_src(instr, 0));
            }
        } else if (instr_get_opcode(instr) == OP_xor &&
                   opnd_is_reg(instr_get_src(instr, 0)) &&
                   opnd_get_reg(instr_get_src(instr, 0)) == REG_ECX &&
                   opnd_is_reg(instr_get_dst(instr, 0)) &&
                   opnd_get_reg(instr_get_dst(instr, 0)) == REG_ECX) {
            /* xor to 0 */
            found_ecx = true;
            info->fixup_index = 0;
        }
        num_instr++;
        if (num_instr > MAX_INSTRS_BEFORE_SYSCALL) /* wrappers should be short! */
            break; /* avoid weird cases like NPXEMULATORTABLE */
    }
    instr_destroy(dcontext, instr);
    return found_syscall;
}