Store pointers to heap data in 32-bit words

Store Erlang terms in 32-bit entities on the heap, expanding the
pointers to 64-bit when needed. This works because all terms are stored
on addresses in the 32-bit address range (the 32 most significant bits
of pointers to term data are always 0).

Introduce a new datatype called UWord (along with its companion SWord),
which is an integer having the exact same size as the machine word
(a void *), but might be larger than Eterm/Uint.

Store code as machine words, as the instructions are pointers to
executable code which might reside outside the 32-bit address range.

Continuation pointers are stored on the 32-bit stack and hence must
point to addresses in the low range, which means that loaded beam code
much be placed in the low 32-bit address range (but, as said earlier,
the instructions themselves are full words).

No Erlang term data can be stored on C stacks (enforced by an
earlier commit).

This version gives a prompt, but test cases still fail (and dump core).

The loader (and emulator loop) has instruction packing disabled.

The main issues has been in rewriting loader and actual virtual
machine. Subsystems (like distribution) does not work yet.

1 files changed, 254 insertions, 225 deletions

diff --git a/erts/emulator/beam/beam_emu.c b/erts/emulator/beam/beam_emu.c
index 66c6eb7819..d542c56e28 100644
--- a/erts/emulator/beam/beam_emu.c
+++ b/erts/emulator/beam/beam_emu.c
@@ -117,6 +117,7 @@ do {                                     \
 #endif
 
 #define GET_BIF_ADDRESS(p) ((BifFunction) (((Export *) p)->code[4]))
+#define TermWords(t) (((t) / (sizeof(UWord)/sizeof(Eterm))) + !!((t) % (sizeof(UWord)/sizeof(Eterm))))
 
 
 /*
@@ -138,8 +139,8 @@ do {                                     \
 #define VALID_INSTR(IP) (0 <= (int)(IP) && ((int)(IP) < (NUMBER_OF_OPCODES*2+10)))
 #else
 #define VALID_INSTR(IP) \
-   ((Sint)LabelAddr(emulator_loop) <= (Sint)(IP) && \
-    (Sint)(IP) < (Sint)LabelAddr(end_emulator_loop))
+   ((SWord)LabelAddr(emulator_loop) <= (SWord)(IP) && \
+    (SWord)(IP) < (SWord)LabelAddr(end_emulator_loop))
 #endif /* NO_JUMP_TABLE */
 
 #define SET_CP(p, ip)           \
@@ -181,11 +182,11 @@ do {                                     \
  
 #define StoreBifResult(Dst, Result)                          \
   do {                                                       \
-    Eterm* stb_next;                                         \
+    UWord* stb_next;                                         \
     Eterm stb_reg;                                           \
     stb_reg = Arg(Dst);                                      \
     I += (Dst) + 2;                                          \
-    stb_next = (Eterm *) *I;                                 \
+    stb_next = (UWord *) *I;                                 \
     CHECK_TERM(Result);                                      \
     switch (beam_reg_tag(stb_reg)) {                         \
     case R_REG_DEF:                                          \
@@ -205,7 +206,7 @@ do {                                     \
       c_p->cp = 0;				\
    } while(0)
 
-#define RESTORE_CP(X)		SET_CP(c_p, cp_val(*(X)))
+#define RESTORE_CP(X)		SET_CP(c_p, (UWord *) cp_val(*(X)))
 
 #define ISCATCHEND(instr) ((Eterm *) *(instr) == OpCode(catch_end_y))
 
@@ -213,13 +214,13 @@ do {                                     \
  * Special Beam instructions.
  */
 
-Eterm beam_apply[2];
-Eterm beam_exit[1];
-Eterm beam_continue_exit[1];
+UWord beam_apply[2];
+UWord beam_exit[1];
+UWord beam_continue_exit[1];
 
-Eterm* em_call_error_handler;
-Eterm* em_apply_bif;
-Eterm* em_call_traced_function;
+UWord* em_call_error_handler;
+UWord* em_apply_bif;
+UWord* em_call_traced_function;
 
 
 /* NOTE These should be the only variables containing trace instructions.
@@ -227,9 +228,9 @@ Eterm* em_call_traced_function;
 **      for the refering variable (one of these), and rouge references
 **      will most likely cause chaos.
 */
-Eterm beam_return_to_trace[1]; /* OpCode(i_return_to_trace) */
-Eterm beam_return_trace[1];    /* OpCode(i_return_trace) */
-Eterm beam_exception_trace[1]; /* UGLY also OpCode(i_return_trace) */
+UWord beam_return_to_trace[1]; /* OpCode(i_return_to_trace) */
+UWord beam_return_trace[1];    /* OpCode(i_return_trace) */
+UWord beam_exception_trace[1]; /* UGLY also OpCode(i_return_trace) */
 
 /*
  * All Beam instructions in numerical order.
@@ -522,8 +523,8 @@ extern int count_instructions;
 
 #define DispatchMacro()				\
   do {						\
-     Eterm* dis_next;				\
-     dis_next = (Eterm *) *I;			\
+     UWord* dis_next;				\
+     dis_next = (UWord *) *I;			\
      CHECK_ARGS(I);				\
      if (FCALLS > 0 || FCALLS > neg_o_reds) {	\
         FCALLS--;				\
@@ -535,8 +536,8 @@ extern int count_instructions;
 
 #define DispatchMacroFun()			\
   do {						\
-     Eterm* dis_next;				\
-     dis_next = (Eterm *) *I;			\
+     UWord* dis_next;				\
+     dis_next = (UWord *) *I;			\
      CHECK_ARGS(I);				\
      if (FCALLS > 0 || FCALLS > neg_o_reds) {	\
         FCALLS--;				\
@@ -590,7 +591,7 @@ extern int count_instructions;
     ASSERT(VALID_INSTR(*I));   \
     Goto(*I)
 
-#define PreFetch(N, Dst) do { Dst = (Eterm *) *(I + N + 1); } while (0)
+#define PreFetch(N, Dst) do { Dst = (UWord *) *(I + N + 1); } while (0)
 #define NextPF(N, Dst)         \
     I += N + 1;                \
     ASSERT(VALID_INSTR(Dst));  \
@@ -644,7 +645,7 @@ extern int count_instructions;
 #define DeallocateReturn(Deallocate)       \
   do {                                     \
     int words_to_pop = (Deallocate);       \
-    SET_I(cp_val(*E));                     \
+    SET_I((UWord *) cp_val(*E));                     \
     E = ADD_BYTE_OFFSET(E, words_to_pop);  \
     CHECK_TERM(r(0));                      \
     Goto(*I);                              \
@@ -657,19 +658,19 @@ extern int count_instructions;
 #define MoveCall(Src, Dest, CallDest, Size)	\
     (Dest) = (Src);				\
     SET_CP(c_p, I+Size+1);			\
-    SET_I((Eterm *) CallDest);			\
+    SET_I((UWord *) CallDest);			\
     Dispatch();
 
 #define MoveCallLast(Src, Dest, CallDest, Deallocate)	\
     (Dest) = (Src);					\
     RESTORE_CP(E);					\
     E = ADD_BYTE_OFFSET(E, (Deallocate));		\
-    SET_I((Eterm *) CallDest);				\
+    SET_I((UWord *) CallDest);				\
     Dispatch();
 
 #define MoveCallOnly(Src, Dest, CallDest)	\
     (Dest) = (Src);				\
-    SET_I((Eterm *) CallDest);			\
+    SET_I((UWord *) CallDest);			\
     Dispatch();
 
 #define GetList(Src, H, T) do {			\
@@ -677,47 +678,48 @@ extern int count_instructions;
    H = CAR(tmp_ptr);				\
    T = CDR(tmp_ptr); } while (0)
 
-#define GetTupleElement(Src, Element, Dest)				  \
-  do {									  \
-    tmp_arg1 = (Eterm) (((unsigned char *) tuple_val(Src)) + (Element));  \
-    (Dest) = (*(Eterm *)tmp_arg1);					  \
+#define GetTupleElement(Src, Element, Dest)				\
+  do {									\
+    tmp_arg1 = (Eterm) COMPRESS_POINTER(((unsigned char *) tuple_val(Src)) + 	\
+				(Element));				\
+    (Dest) = (*(Eterm *) EXPAND_POINTER(tmp_arg1));			\
   } while (0)
 
-#define ExtractNextElement(Dest)				\
-    tmp_arg1 += sizeof(Eterm);					\
-    (Dest) = (* (Eterm *) (((unsigned char *) tmp_arg1)))
+#define ExtractNextElement(Dest)					  \
+    tmp_arg1 += sizeof(Eterm);						  \
+    (Dest) = (* (Eterm *) (((unsigned char *) EXPAND_POINTER(tmp_arg1))))
 
-#define ExtractNextElement2(Dest)		\
-  do {						\
-    Eterm* ene_dstp = &(Dest);			\
-    ene_dstp[0] = ((Eterm *) tmp_arg1)[1];	\
-    ene_dstp[1] = ((Eterm *) tmp_arg1)[2];	\
-    tmp_arg1 += sizeof(Eterm) + sizeof(Eterm);	\
+#define ExtractNextElement2(Dest)				\
+  do {								\
+    Eterm* ene_dstp = &(Dest);					\
+    ene_dstp[0] = ((Eterm *) EXPAND_POINTER(tmp_arg1))[1];	\
+    ene_dstp[1] = ((Eterm *) EXPAND_POINTER(tmp_arg1))[2];	\
+    tmp_arg1 += sizeof(Eterm) + sizeof(Eterm);			\
   } while (0)
 
 #define ExtractNextElement3(Dest)		\
   do {						\
     Eterm* ene_dstp = &(Dest);			\
-    ene_dstp[0] = ((Eterm *) tmp_arg1)[1];	\
-    ene_dstp[1] = ((Eterm *) tmp_arg1)[2];	\
-    ene_dstp[2] = ((Eterm *) tmp_arg1)[3];	\
+    ene_dstp[0] = ((Eterm *) EXPAND_POINTER(tmp_arg1))[1];	\
+    ene_dstp[1] = ((Eterm *) EXPAND_POINTER(tmp_arg1))[2];	\
+    ene_dstp[2] = ((Eterm *) EXPAND_POINTER(tmp_arg1))[3];	\
     tmp_arg1 += 3*sizeof(Eterm);		\
   } while (0)
 
 #define ExtractNextElement4(Dest)		\
   do {						\
     Eterm* ene_dstp = &(Dest);			\
-    ene_dstp[0] = ((Eterm *) tmp_arg1)[1];	\
-    ene_dstp[1] = ((Eterm *) tmp_arg1)[2];	\
-    ene_dstp[2] = ((Eterm *) tmp_arg1)[3];	\
-    ene_dstp[3] = ((Eterm *) tmp_arg1)[4];	\
+    ene_dstp[0] = ((Eterm *) EXPAND_POINTER(tmp_arg1))[1];	\
+    ene_dstp[1] = ((Eterm *) EXPAND_POINTER(tmp_arg1))[2];	\
+    ene_dstp[2] = ((Eterm *) EXPAND_POINTER(tmp_arg1))[3];	\
+    ene_dstp[3] = ((Eterm *) EXPAND_POINTER(tmp_arg1))[4];	\
     tmp_arg1 += 4*sizeof(Eterm);		\
   } while (0)
 
 #define ExtractElement(Element, Dest)		\
   do {						\
      tmp_arg1 += (Element);			\
-     (Dest) = (* (Eterm *) tmp_arg1);		\
+     (Dest) = (* (Eterm *) EXPAND_POINTER(tmp_arg1));		\
   } while (0)
 
 #define PutTuple(Arity, Src, Dest)		\
@@ -759,8 +761,13 @@ extern int count_instructions;
 
 #define IsTuple(X, Action) if (is_not_tuple(X)) Action
 
-#define IsArity(Pointer, Arity, Fail) \
-    if (*(Eterm *)(tmp_arg1 = (Eterm)tuple_val(Pointer)) != (Arity)) { Fail; }
+#define IsArity(Pointer, Arity, Fail)					  \
+    if (*(Eterm *)							  \
+	EXPAND_POINTER(tmp_arg1 = (Eterm) 				  \
+		       COMPRESS_POINTER(tuple_val(Pointer))) != (Arity))  \
+    { 									  \
+        Fail; 								  \
+    }
 
 #define IsFunction(X, Action)			\
   do {						\
@@ -776,11 +783,14 @@ extern int count_instructions;
      }						\
   } while (0)
 
-#define IsTupleOfArity(Src, Arity, Fail) \
-  do { \
-    if (is_not_tuple(Src) || *(Eterm *)(tmp_arg1 = (Eterm) tuple_val(Src)) != Arity) { \
-        Fail; \
-    } \
+#define IsTupleOfArity(Src, Arity, Fail)				      \
+  do {									      \
+    if (is_not_tuple(Src) || 						      \
+	*(Eterm *)							      \
+	EXPAND_POINTER(tmp_arg1 = 					      \
+		       (Eterm) COMPRESS_POINTER(tuple_val(Src))) != Arity) { \
+        Fail;								      \
+    }									      \
   } while (0)
 
 #define IsBoolean(X, Fail) if ((X) != am_true && (X) != am_false) { Fail; }
@@ -791,7 +801,7 @@ extern int count_instructions;
 #define IsBitstring(Src, Fail) \
   if (is_not_binary(Src)) { Fail; }
 
-#ifdef ARCH_64
+#if defined(ARCH_64) && !HALFWORD_HEAP
 #define BsSafeMul(A, B, Fail, Target)		\
    do { Uint64 _res = (A) * (B);		\
       if (_res / B != A) { Fail; }		\
@@ -974,23 +984,23 @@ extern int count_instructions;
 #define IsRef(Src, Fail) if (is_not_ref(Src)) { Fail; }
 
 static BifFunction translate_gc_bif(void* gcf);
-static Eterm* handle_error(Process* c_p, Eterm* pc, Eterm* reg, BifFunction bf);
-static Eterm* next_catch(Process* c_p, Eterm *reg);
+static UWord* handle_error(Process* c_p, UWord* pc, Eterm* reg, BifFunction bf);
+static UWord* next_catch(Process* c_p, Eterm *reg);
 static void terminate_proc(Process* c_p, Eterm Value);
 static Eterm add_stacktrace(Process* c_p, Eterm Value, Eterm exc);
-static void save_stacktrace(Process* c_p, Eterm* pc, Eterm* reg,
+static void save_stacktrace(Process* c_p, UWord* pc, Eterm* reg,
 			     BifFunction bf, Eterm args);
 static struct StackTrace * get_trace_from_exc(Eterm exc);
 static Eterm make_arglist(Process* c_p, Eterm* reg, int a);
-static Eterm call_error_handler(Process* p, Eterm* ip, Eterm* reg);
-static Eterm call_breakpoint_handler(Process* p, Eterm* fi, Eterm* reg);
-static Uint* fixed_apply(Process* p, Eterm* reg, Uint arity);
-static Eterm* apply(Process* p, Eterm module, Eterm function,
+static Eterm call_error_handler(Process* p, UWord* ip, Eterm* reg);
+static Eterm call_breakpoint_handler(Process* p, UWord* fi, Eterm* reg);
+static UWord* fixed_apply(Process* p, Eterm* reg, Uint arity);
+static UWord* apply(Process* p, Eterm module, Eterm function,
 		     Eterm args, Eterm* reg);
 static int hibernate(Process* c_p, Eterm module, Eterm function,
 		     Eterm args, Eterm* reg);
-static Eterm* call_fun(Process* p, int arity, Eterm* reg, Eterm args);
-static Eterm* apply_fun(Process* p, Eterm fun, Eterm args, Eterm* reg);
+static UWord* call_fun(Process* p, int arity, Eterm* reg, Eterm args);
+static UWord* apply_fun(Process* p, Eterm fun, Eterm args, Eterm* reg);
 static Eterm new_fun(Process* p, Eterm* reg, ErlFunEntry* fe, int num_free);
 
 #if defined(_OSE_) || defined(VXWORKS)
@@ -1078,7 +1088,7 @@ void process_main(void)
     /*
      * Pointer to next threaded instruction.
      */
-    register Eterm *I REG_I = NULL;
+    register UWord *I REG_I = NULL;
 
     /* Number of reductions left.  This function
      * returns to the scheduler when FCALLS reaches zero.
@@ -1097,6 +1107,7 @@ void process_main(void)
 #endif
 
 #ifndef ERTS_SMP
+#if !HALFWORD_HEAP
     static Eterm save_reg[ERTS_X_REGS_ALLOCATED];
     /* X registers -- not used directly, but
      * through 'reg', because using it directly
@@ -1104,7 +1115,7 @@ void process_main(void)
      * while using it through reg needs only
      * one.
      */
-
+#endif
     /*
      * Floating point registers.
      */
@@ -1150,7 +1161,12 @@ void process_main(void)
 	goto init_emulator;
     }
 #ifndef ERTS_SMP
+#if !HALFWORD_HEAP
     reg = save_reg;	/* XXX: probably wastes a register on x86 */
+#else
+    /* Registers need to be heap allocated (correct memory range) for tracing to work */
+    reg = erts_alloc(ERTS_ALC_T_BEAM_REGISTER, ERTS_X_REGS_ALLOCATED * sizeof(Eterm));
+#endif
 #endif
     c_p = NULL;
     reds_used = 0;
@@ -1178,7 +1194,7 @@ void process_main(void)
     {
 	int reds;
 	Eterm* argp;
-	Eterm* next;
+	UWord *next;
 	int i;
 
 	argp = c_p->arg_reg;
@@ -1205,7 +1221,7 @@ void process_main(void)
 	    FCALLS = REDS_IN(c_p) = reds;
 	}
 
-	next = (Eterm *) *I;
+	next = (UWord *) *I;
 	r(0) = c_p->arg_reg[0];
 #ifdef HARDDEBUG
 	if (c_p->arity > 0) {
@@ -1297,7 +1313,7 @@ void process_main(void)
  }
  /* FALL THROUGH */
  OpCase(i_call_only_f): {
-     SET_I((Eterm *) Arg(0));
+     SET_I((UWord *) Arg(0));
      Dispatch();
  }
 
@@ -1308,7 +1324,7 @@ void process_main(void)
  OpCase(i_call_last_fP): {
      RESTORE_CP(E);
      E = ADD_BYTE_OFFSET(E, Arg(1));
-     SET_I((Eterm *) Arg(0));
+     SET_I((UWord *) Arg(0));
      Dispatch();
  }
 
@@ -1319,7 +1335,7 @@ void process_main(void)
  /* FALL THROUGH */
  OpCase(i_call_f): {
      SET_CP(c_p, I+2);
-     SET_I((Eterm *) Arg(0));
+     SET_I((UWord *) Arg(0));
      Dispatch();
  }
 
@@ -1355,7 +1371,7 @@ void process_main(void)
     Dispatchx();
 
  OpCase(init_y): {
-     Eterm* next;
+     UWord *next;
 
      PreFetch(1, next);
      make_blank(yb(Arg(0)));
@@ -1363,7 +1379,7 @@ void process_main(void)
  }
 
  OpCase(i_trim_I): {
-     Eterm* next;
+     UWord *next;
      Uint words;
      Uint cp;
 
@@ -1389,7 +1405,7 @@ void process_main(void)
  }
 
  OpCase(test_heap_1_put_list_Iy): {
-     Eterm* next;
+     UWord *next;
 
      PreFetch(2, next);
      TestHeap(Arg(0), 1);
@@ -1420,7 +1436,7 @@ void process_main(void)
      */
 
  OpCase(send): {
-     Eterm* next;
+     UWord *next;
      Eterm result;
 
      PRE_BIF_SWAPOUT(c_p);
@@ -1435,7 +1451,7 @@ void process_main(void)
 	 NextPF(0, next);
      } else if (c_p->freason == TRAP) {
 	 SET_CP(c_p, I+1);
-	 SET_I((Eterm *) c_p->def_arg_reg[3]);
+	 SET_I(*((UWord **) (UWord) ((c_p)->def_arg_reg + 3)));
 	 SWAPIN;
 	 r(0) = c_p->def_arg_reg[0];
 	 x(1) = c_p->def_arg_reg[1];
@@ -1561,7 +1577,7 @@ void process_main(void)
      */
  OpCase(i_loop_rec_fr):
  {
-     Eterm* next;
+     UWord *next;
      ErlMessage* msgp;
 
  loop_rec__:
@@ -1585,7 +1601,7 @@ void process_main(void)
 	     erts_smp_proc_unlock(c_p, ERTS_PROC_LOCKS_MSG_RECEIVE);
 	 else {
 #endif
-	     SET_I((Eterm *) Arg(0));
+	     SET_I((UWord *) Arg(0));
 	     Goto(*I);		/* Jump to a wait or wait_timeout instruction */
 #ifdef ERTS_SMP
 	 }
@@ -1621,7 +1637,7 @@ void process_main(void)
   * Remove a (matched) message from the message queue.
   */
  OpCase(remove_message): {
-     Eterm* next;
+     UWord *next;
      ErlMessage* msgp;
 
      PROCESS_MAIN_CHK_LOCKS(c_p);
@@ -1666,7 +1682,7 @@ void process_main(void)
      * message didn't match), then jump to the loop_rec instruction.
      */
  OpCase(loop_rec_end_f): {
-     SET_I((Eterm *) Arg(0));
+     SET_I((UWord *) Arg(0));
      SAVE_MESSAGE(c_p);
      goto loop_rec__;
  }
@@ -1696,12 +1712,12 @@ void process_main(void)
      }
      GetArg1(1, timeout_value);
      if (timeout_value != make_small(0)) {
-#if !defined(ARCH_64)
+#if !defined(ARCH_64) || HALFWORD_HEAP
 	 Uint time_val;
 #endif
 
 	 if (is_small(timeout_value) && signed_val(timeout_value) > 0 &&
-#if defined(ARCH_64)
+#if defined(ARCH_64) && !HALFWORD_HEAP
 	     ((unsigned_val(timeout_value) >> 32) == 0)
 #else
 	     1
@@ -1712,14 +1728,16 @@ void process_main(void)
 	      * c_p->def_arg_reg[0].  Note that it is safe to use this
 	      * location because there are no living x registers in
 	      * a receive statement.
+	      * Note that for the halfword emulator, the two first elements
+	      * of the array are used.
 	      */
-	     c_p->def_arg_reg[0] = (Eterm) (I+3);
+	     *((UWord **) (UWord) c_p->def_arg_reg) = I+3;
 	     set_timer(c_p, unsigned_val(timeout_value));
 	 } else if (timeout_value == am_infinity) {
 	     c_p->flags |= F_TIMO;
-#if !defined(ARCH_64)
+#if !defined(ARCH_64) || HALFWORD_HEAP
 	 } else if (term_to_Uint(timeout_value, &time_val)) {
-	     c_p->def_arg_reg[0] = (Eterm) (I+3);
+	     *((UWord **) (UWord) c_p->def_arg_reg) = I+3;
 	     set_timer(c_p, time_val);
 #endif
 	 } else {		/* Wrong time */
@@ -1748,7 +1766,7 @@ void process_main(void)
 
 	 wait2: {
 	     ASSERT(!ERTS_PROC_IS_EXITING(c_p));
-	     c_p->i = (Eterm *) Arg(0); /* L1 */
+	     c_p->i = (UWord *) Arg(0); /* L1 */
 	     SWAPOUT;
 	     c_p->arity = 0;
 	     c_p->status = P_WAITING;
@@ -1776,7 +1794,7 @@ void process_main(void)
       * we must test the F_INSLPQUEUE flag as well as the F_TIMO flag.
       */
      if ((c_p->flags & (F_INSLPQUEUE | F_TIMO)) == 0) {
-	 c_p->def_arg_reg[0] = (Eterm) (I+3);
+	 *((UWord **) (UWord) c_p->def_arg_reg) = I+3;
 	 set_timer(c_p, Arg(1));
      }
      goto wait2;
@@ -1791,7 +1809,7 @@ void process_main(void)
  }
 
  OpCase(timeout): {
-     Eterm* next;
+     UWord *next;
 
      PreFetch(0, next);
      if (IS_TRACED_FL(c_p, F_TRACE_RECEIVE)) {
@@ -1811,8 +1829,8 @@ void process_main(void)
  do_binary_search:
  {
      struct Pairs {
-	 Eterm val;
-	 Eterm* addr;
+	 UWord val;
+	 UWord* addr;
      };
      struct Pairs* low;
      struct Pairs* high;
@@ -1852,7 +1870,7 @@ void process_main(void)
 	     Goto(*I);
 	 }
      }
-     SET_I((Eterm *) Arg(1));
+     SET_I((UWord *) Arg(1));
      Goto(*I);
  }
 
@@ -1864,11 +1882,11 @@ void process_main(void)
      if (is_small(index)) {
 	 index = signed_val(index);
 	 if (index < Arg(2)) {
-	     SET_I((Eterm *) (&Arg(3))[index]);
+	     SET_I((UWord *) (&Arg(3))[index]);
 	     Goto(*I);
 	 }
      }
-     SET_I((Eterm *) Arg(1));
+     SET_I((UWord *) Arg(1));
      Goto(*I);
  }
 
@@ -1880,11 +1898,11 @@ void process_main(void)
      if (is_small(index)) {
 	 index = (Uint) (signed_val(index) - Arg(3));
 	 if (index < Arg(2)) {
-	     SET_I((Eterm *) (&Arg(4))[index]);
+	     SET_I((UWord *) (&Arg(4))[index]);
 	     Goto(*I);
 	 }
      }
-     SET_I((Eterm *) Arg(1));
+     SET_I((UWord *) Arg(1));
      Goto(*I);
  }
 
@@ -1921,7 +1939,7 @@ void process_main(void)
 	if (is_value(result)) {
 	    StoreBifResult(3, result);
 	}
-	SET_I((Eterm *) Arg(0));
+	SET_I((UWord *) Arg(0));
 	Goto(*I);
     }
 
@@ -1982,7 +2000,7 @@ void process_main(void)
 	    StoreBifResult(4, result);
 	}
 	if (Arg(0) != 0) {
-	    SET_I((Eterm *) Arg(0));
+	    SET_I((UWord *) Arg(0));
 	    Goto(*I);
 	}
 	reg[0] = arg;
@@ -2010,7 +2028,7 @@ void process_main(void)
 	if (is_value(result)) {
 	    StoreBifResult(2, result);
 	}
-	SET_I((Eterm *) Arg(0));
+	SET_I((UWord *) Arg(0));
 	Goto(*I);
     }
 
@@ -2046,7 +2064,7 @@ void process_main(void)
      */
  OpCase(call_bif0_e):
     {
-	Eterm (*bf)(Process*, Uint*) = GET_BIF_ADDRESS(Arg(0));
+	Eterm (*bf)(Process*, UWord*) = GET_BIF_ADDRESS(Arg(0));
 
 	PRE_BIF_SWAPOUT(c_p);
 	c_p->fcalls = FCALLS - 1;
@@ -2079,9 +2097,9 @@ void process_main(void)
 
  OpCase(call_bif1_e):
     {
-	Eterm (*bf)(Process*, Eterm, Uint*) = GET_BIF_ADDRESS(Arg(0));
+	Eterm (*bf)(Process*, Eterm, UWord*) = GET_BIF_ADDRESS(Arg(0));
 	Eterm result;
-	Eterm* next;
+	UWord *next;
 
 	c_p->fcalls = FCALLS - 1;
 	if (FCALLS <= 0) {
@@ -2114,9 +2132,9 @@ void process_main(void)
 
  OpCase(call_bif2_e):
     {
-	Eterm (*bf)(Process*, Eterm, Eterm, Uint*) = GET_BIF_ADDRESS(Arg(0));
+	Eterm (*bf)(Process*, Eterm, Eterm, UWord*) = GET_BIF_ADDRESS(Arg(0));
 	Eterm result;
-	Eterm* next;
+	UWord *next;
 
 	PRE_BIF_SWAPOUT(c_p);
 	c_p->fcalls = FCALLS - 1;
@@ -2151,9 +2169,9 @@ void process_main(void)
 
  OpCase(call_bif3_e):
     {
-	Eterm (*bf)(Process*, Eterm, Eterm, Eterm, Uint*) = GET_BIF_ADDRESS(Arg(0));
+	Eterm (*bf)(Process*, Eterm, Eterm, Eterm, UWord*) = GET_BIF_ADDRESS(Arg(0));
 	Eterm result;
-	Eterm* next;
+	UWord *next;
 
 	PRE_BIF_SWAPOUT(c_p);
 	c_p->fcalls = FCALLS - 1;
@@ -2174,7 +2192,7 @@ void process_main(void)
 	} else if (c_p->freason == TRAP) {
 	call_bif_trap3:
 	    SET_CP(c_p, I+2);
-	    SET_I((Eterm *)c_p->def_arg_reg[3]);
+	    SET_I(*((UWord **) (UWord) ((c_p)->def_arg_reg + 3)));
 	    SWAPIN;
 	    r(0) = c_p->def_arg_reg[0];
 	    x(1) = c_p->def_arg_reg[1];
@@ -2282,7 +2300,7 @@ void process_main(void)
  lb_Cl_error: {
      if (Arg(0) != 0) {
 	 OpCase(jump_f): {
-	     SET_I((Eterm *) Arg(0));
+	     SET_I((UWord *) Arg(0));
 	     Goto(*I);
 	 }
      }
@@ -2474,7 +2492,7 @@ void process_main(void)
     goto lb_Cl_error;
 
  OpCase(i_apply): {
-     Eterm* next;
+     UWord *next;
      SWAPOUT;
      next = apply(c_p, r(0), x(1), x(2), reg);
      SWAPIN;
@@ -2489,13 +2507,13 @@ void process_main(void)
  }
 
  OpCase(i_apply_last_P): {
-     Eterm* next;
+     UWord *next;
      SWAPOUT;
      next = apply(c_p, r(0), x(1), x(2), reg);
      SWAPIN;
      if (next != NULL) {
 	 r(0) = reg[0];
-	 SET_CP(c_p, (Eterm *) E[0]);
+	 SET_CP(c_p, (UWord *) EXPAND_POINTER(E[0]));
 	 E = ADD_BYTE_OFFSET(E, Arg(0));
 	 SET_I(next);
 	 Dispatch();
@@ -2505,7 +2523,7 @@ void process_main(void)
  }
 
  OpCase(i_apply_only): {
-     Eterm* next;
+     UWord *next;
      SWAPOUT;
      next = apply(c_p, r(0), x(1), x(2), reg);
      SWAPIN;
@@ -2519,7 +2537,7 @@ void process_main(void)
  }
 
  OpCase(apply_I): {
-     Eterm* next;
+     UWord *next;
 
      reg[0] = r(0);
      SWAPOUT;
@@ -2536,7 +2554,7 @@ void process_main(void)
  }
 
  OpCase(apply_last_IP): {
-     Eterm* next;
+     UWord *next;
 
      reg[0] = r(0);
      SWAPOUT;
@@ -2544,7 +2562,7 @@ void process_main(void)
      SWAPIN;
      if (next != NULL) {
 	 r(0) = reg[0];
-	 SET_CP(c_p, (Eterm *) E[0]);
+	 SET_CP(c_p, (UWord *) EXPAND_POINTER(E[0]));
 	 E = ADD_BYTE_OFFSET(E, Arg(1));
 	 SET_I(next);
 	 Dispatch();
@@ -2554,7 +2572,7 @@ void process_main(void)
  }
 
  OpCase(i_apply_fun): {
-     Eterm* next;
+     UWord *next;
 
      SWAPOUT;
      next = apply_fun(c_p, r(0), x(1), reg);
@@ -2569,14 +2587,14 @@ void process_main(void)
  }
 
  OpCase(i_apply_fun_last_P): {
-     Eterm* next;
+     UWord *next;
 
      SWAPOUT;
      next = apply_fun(c_p, r(0), x(1), reg);
      SWAPIN;
      if (next != NULL) {
 	 r(0) = reg[0];
-	 SET_CP(c_p, (Eterm *) E[0]);
+	 SET_CP(c_p, (UWord *) EXPAND_POINTER(E[0]));
 	 E = ADD_BYTE_OFFSET(E, Arg(0));
 	 SET_I(next);
 	 Dispatchfun();
@@ -2585,7 +2603,7 @@ void process_main(void)
  }
 
  OpCase(i_apply_fun_only): {
-     Eterm* next;
+     UWord *next;
 
      SWAPOUT;
      next = apply_fun(c_p, r(0), x(1), reg);
@@ -2599,7 +2617,7 @@ void process_main(void)
  }
 
  OpCase(i_call_fun_I): {
-     Eterm* next;
+     UWord *next;
 
      SWAPOUT;
      reg[0] = r(0);
@@ -2615,7 +2633,7 @@ void process_main(void)
  }
 
  OpCase(i_call_fun_last_IP): {
-     Eterm* next;
+     UWord *next;
 
      SWAPOUT;
      reg[0] = r(0);
@@ -2623,7 +2641,7 @@ void process_main(void)
      SWAPIN;
      if (next != NULL) {
 	r(0) = reg[0];
-	SET_CP(c_p, (Eterm *) E[0]);
+	SET_CP(c_p, (UWord *) EXPAND_POINTER(E[0]));
 	E = ADD_BYTE_OFFSET(E, Arg(1));
 	SET_I(next);
 	Dispatchfun();
@@ -2728,7 +2746,7 @@ void process_main(void)
 	 tmp_arg1 = *tuple_val(tmp_arg1);
 	 goto do_binary_search;
      }
-     SET_I((Eterm *) Arg(1));
+     SET_I((UWord *) Arg(1));
      Goto(*I);
  }     
 
@@ -2754,13 +2772,15 @@ void process_main(void)
  	    given = big_val(tmp_arg1);
 	    given_arity = given[0];
 	    given_size = thing_arityval(given_arity);
-	    bigp = &Arg(2);
+	    bigp = (Eterm *) &Arg(2);
 	    while ((arity = bigp[0]) > given_arity) {
 		bigp += thing_arityval(arity) + 2;
 	    }
 	    while (bigp[0] == given_arity) {
 		if (memcmp(bigp+1, given+1, sizeof(Eterm)*given_size) == 0) {
-		    SET_I((Eterm *) bigp[given_size+1]);
+		    UWord *tmp =
+			((UWord *) (UWord) bigp) + TermWords(given_size + 1);
+		    SET_I((UWord *) *tmp);
 		    Goto(*I);
 		}
 		bigp += thing_arityval(arity) + 2;
@@ -2771,18 +2791,18 @@ void process_main(void)
 	 * Failed.
 	 */
 
-	SET_I((Eterm *) Arg(1));
+	SET_I((UWord *) Arg(1));
 	Goto(*I);
     }
 
-#ifdef ARCH_64
+#if defined(ARCH_64) && !HALFWORD_HEAP
  OpCase(i_select_float_sfI):
  {
      Uint f;
      int n;
      struct ValLabel {
 	 Uint f;
-	 Eterm* addr;
+	 UWord* addr;
      };
      struct ValLabel* ptr;
 
@@ -2810,7 +2830,7 @@ void process_main(void)
      struct ValLabel {
 	 Uint fpart1;
 	 Uint fpart2;
-	 Eterm* addr;
+	 UWord* addr;
      };
      struct ValLabel* ptr;
 
@@ -2828,7 +2848,7 @@ void process_main(void)
 	 }
 	 ptr++;
      }
-     SET_I((Eterm *) Arg(1));
+     SET_I((UWord *) Arg(1));
      Goto(*I);
  }
 #endif
@@ -2836,7 +2856,7 @@ void process_main(void)
  OpCase(set_tuple_element_sdP): {
      Eterm element;
      Eterm tuple;
-     Eterm* next;
+     UWord *next;
      Eterm* p;
      
      PreFetch(3, next);
@@ -3031,7 +3051,7 @@ void process_main(void)
 	switch (tmp_arg2) {
 	case 3:
 	    {
-		Eterm (*bf)(Process*, Eterm, Eterm, Eterm, Uint*) = vbf;
+		Eterm (*bf)(Process*, Eterm, Eterm, Eterm, UWord*) = vbf;
 		ASSERT(!ERTS_PROC_IS_EXITING(c_p));
 		tmp_arg1 = (*bf)(c_p, r(0), x(1), x(2), I);
 		ASSERT(!ERTS_PROC_IS_EXITING(c_p) || is_non_value(tmp_arg1));
@@ -3040,7 +3060,7 @@ void process_main(void)
 	    break;
 	case 2:
 	    {
-		Eterm (*bf)(Process*, Eterm, Eterm, Uint*) = vbf;
+		Eterm (*bf)(Process*, Eterm, Eterm, UWord*) = vbf;
 		ASSERT(!ERTS_PROC_IS_EXITING(c_p));
 		tmp_arg1 = (*bf)(c_p, r(0), x(1), I);
 		ASSERT(!ERTS_PROC_IS_EXITING(c_p) || is_non_value(tmp_arg1));
@@ -3049,7 +3069,7 @@ void process_main(void)
 	    break;
 	case 1:
 	    {
-		Eterm (*bf)(Process*, Eterm, Uint*) = vbf;
+		Eterm (*bf)(Process*, Eterm, UWord*) = vbf;
 		ASSERT(!ERTS_PROC_IS_EXITING(c_p));
 		tmp_arg1 = (*bf)(c_p, r(0), I);
 		ASSERT(!ERTS_PROC_IS_EXITING(c_p) || is_non_value(tmp_arg1));
@@ -3058,7 +3078,7 @@ void process_main(void)
 	    break;
 	case 0:
 	    {
-		Eterm (*bf)(Process*, Uint*) = vbf;
+		Eterm (*bf)(Process*, UWord*) = vbf;
 		ASSERT(!ERTS_PROC_IS_EXITING(c_p));
 		tmp_arg1 = (*bf)(c_p, I);
 		ASSERT(!ERTS_PROC_IS_EXITING(c_p) || is_non_value(tmp_arg1));
@@ -3082,7 +3102,7 @@ apply_bif_or_nif_epilogue:
 	    SET_I(c_p->cp);
 	    Goto(*I);
 	} else if (c_p->freason == TRAP) {
-	    SET_I((Eterm *)c_p->def_arg_reg[3]);
+	    SET_I(*((UWord **) (UWord) ((c_p)->def_arg_reg + 3)));
 	    r(0) = c_p->def_arg_reg[0];
 	    x(1) = c_p->def_arg_reg[1];
 	    x(2) = c_p->def_arg_reg[2];
@@ -3540,7 +3560,7 @@ apply_bif_or_nif_epilogue:
 
  OpCase(bs_put_string_II):
     {
-	Eterm* next;
+	UWord *next;
 	PreFetch(2, next);
 	erts_new_bs_put_string(ERL_BITS_ARGS_2((byte *) Arg(1), Arg(0)));
 	NextPF(2, next);
@@ -3711,7 +3731,7 @@ apply_bif_or_nif_epilogue:
 
  {
      Eterm header;
-     Eterm* next;
+     UWord *next;
      Uint slots;
 
      OpCase(i_bs_start_match2_rfIId): {
@@ -3777,7 +3797,7 @@ apply_bif_or_nif_epilogue:
  }
 
  OpCase(bs_test_zero_tail2_fr): {
-     Eterm* next;
+     UWord *next;
      ErlBinMatchBuffer *_mb;
      
      PreFetch(1, next);
@@ -3789,7 +3809,7 @@ apply_bif_or_nif_epilogue:
  }
 
  OpCase(bs_test_zero_tail2_fx): {
-     Eterm* next;
+     UWord *next;
      ErlBinMatchBuffer *_mb;
      
      PreFetch(2, next);
@@ -3801,7 +3821,7 @@ apply_bif_or_nif_epilogue:
  }
 
  OpCase(bs_test_tail_imm2_frI): {
-     Eterm* next;
+     UWord *next;
      ErlBinMatchBuffer *_mb;
      PreFetch(2, next);
      _mb = ms_matchbuffer(r(0));
@@ -3811,7 +3831,7 @@ apply_bif_or_nif_epilogue:
      NextPF(2, next);
  }
  OpCase(bs_test_tail_imm2_fxI): {
-     Eterm* next;
+     UWord *next;
      ErlBinMatchBuffer *_mb;
      PreFetch(3, next);
      _mb = ms_matchbuffer(xb(Arg(1)));
@@ -3822,7 +3842,7 @@ apply_bif_or_nif_epilogue:
  }
 
  OpCase(bs_test_unit_frI): {
-     Eterm* next;
+     UWord *next;
      ErlBinMatchBuffer *_mb;
      PreFetch(2, next);
      _mb = ms_matchbuffer(r(0));
@@ -3832,7 +3852,7 @@ apply_bif_or_nif_epilogue:
      NextPF(2, next);
  }
  OpCase(bs_test_unit_fxI): {
-     Eterm* next;
+     UWord *next;
      ErlBinMatchBuffer *_mb;
      PreFetch(3, next);
      _mb = ms_matchbuffer(xb(Arg(1)));
@@ -3843,7 +3863,7 @@ apply_bif_or_nif_epilogue:
  }
 
  OpCase(bs_test_unit8_fr): {
-     Eterm* next;
+     UWord *next;
      ErlBinMatchBuffer *_mb;
      PreFetch(1, next);
      _mb = ms_matchbuffer(r(0));
@@ -3853,7 +3873,7 @@ apply_bif_or_nif_epilogue:
      NextPF(1, next);
  }
  OpCase(bs_test_unit8_fx): {
-     Eterm* next;
+     UWord *next;
      ErlBinMatchBuffer *_mb;
      PreFetch(2, next);
      _mb = ms_matchbuffer(xb(Arg(1)));
@@ -3937,11 +3957,11 @@ apply_bif_or_nif_epilogue:
 	 _integer = get_int32(_mb->base + _mb->offset/8);
      }
      _mb->offset += 32;
-#ifndef ARCH_64
+#if !defined(ARCH_64) || HALFWORD_HEAP
      if (IS_USMALL(0, _integer)) {
 #endif
 	 _result = make_small(_integer);
-#ifndef ARCH_64
+#if !defined(ARCH_64) || HALFWORD_HEAP
      } else {
 	 TestHeap(BIG_UINT_HEAP_SIZE, Arg(1));
 	 _result = uint_to_big((Uint) _integer, HTOP);
@@ -4178,7 +4198,7 @@ apply_bif_or_nif_epilogue:
 
  do_bs_match_string:
      {
-	 Eterm* next;
+	 UWord *next;
 	 byte* bytes;
 	 Uint bits;
 	 ErlBinMatchBuffer* mb;
@@ -4205,7 +4225,7 @@ apply_bif_or_nif_epilogue:
  }
 
  OpCase(i_bs_save2_rI): {
-     Eterm* next;
+     UWord *next;
      ErlBinMatchState *_ms;
      PreFetch(1, next);
      _ms = (ErlBinMatchState*) boxed_val((Eterm) r(0));
@@ -4213,7 +4233,7 @@ apply_bif_or_nif_epilogue:
      NextPF(1, next);
  }
  OpCase(i_bs_save2_xI): {
-     Eterm* next;
+     UWord *next;
      ErlBinMatchState *_ms;
      PreFetch(2, next);
      _ms = (ErlBinMatchState*) boxed_val((Eterm) xb(Arg(0)));
@@ -4222,7 +4242,7 @@ apply_bif_or_nif_epilogue:
  }
 
  OpCase(i_bs_restore2_rI): {
-     Eterm* next;
+     UWord *next;
      ErlBinMatchState *_ms;
      PreFetch(1, next);
      _ms = (ErlBinMatchState*) boxed_val((Eterm) r(0));
@@ -4230,7 +4250,7 @@ apply_bif_or_nif_epilogue:
      NextPF(1, next);
  }
  OpCase(i_bs_restore2_xI): {
-     Eterm* next;
+     UWord *next;
      ErlBinMatchState *_ms;
      PreFetch(2, next);
      _ms = (ErlBinMatchState*) boxed_val((Eterm) xb(Arg(0)));
@@ -4247,7 +4267,7 @@ apply_bif_or_nif_epilogue:
   * deallocate not followed by a return, and that should work.
   */
  OpCase(deallocate_I): {
-     Eterm* next;
+     UWord *next;
 
      PreFetch(1, next);
      D(Arg(0));
@@ -4297,26 +4317,25 @@ apply_bif_or_nif_epilogue:
 	     }
 	     E -= 3;
 	     ASSERT(c_p->htop <= E && E <= c_p->hend);
-	     ASSERT(is_CP((Eterm)(ep->code)));
+	     ASSERT(is_CP((UWord)(ep->code)));
 	     ASSERT(is_internal_pid(c_p->tracer_proc) || 
 		    is_internal_port(c_p->tracer_proc));
-	     E[2] = make_cp(c_p->cp);
+	     E[2] = make_cp(c_p->cp); /* XXX:PaN - code in lower range on halfword */
 	     E[1] = am_true; /* Process tracer */
 	     E[0] = make_cp(ep->code);
-	     c_p->cp = (Eterm*)
-		 make_cp(flags & MATCH_SET_EXCEPTION_TRACE
-			 ? beam_exception_trace : beam_return_trace);
+	     c_p->cp = (flags & MATCH_SET_EXCEPTION_TRACE)
+		 ? beam_exception_trace : beam_return_trace;
 	     erts_smp_proc_lock(c_p, ERTS_PROC_LOCKS_ALL_MINOR);
 	     c_p->trace_flags |= F_EXCEPTION_TRACE;
 	     erts_smp_proc_unlock(c_p, ERTS_PROC_LOCKS_ALL_MINOR);
 	 }
      }
-     SET_I((Uint *) Arg(0));
+     SET_I((UWord *)Arg(0));
      Dispatch();
  }
 
  OpCase(return_trace): {
-     Uint* code = (Uint *) E[0];
+     UWord* code = (UWord *) (UWord) E[0];
      
      SWAPOUT;		/* Needed for shared heap */
      ERTS_SMP_UNREQ_PROC_MAIN_LOCK(c_p);
@@ -4324,24 +4343,24 @@ apply_bif_or_nif_epilogue:
      ERTS_SMP_REQ_PROC_MAIN_LOCK(c_p);
      SWAPIN;
      c_p->cp = NULL;
-     SET_I((Eterm *) E[2]);
+     SET_I((UWord *) cp_val(E[2]));
      E += 3;
      Goto(*I);
  }
 
  OpCase(i_count_breakpoint): {
-     Uint real_I;
+     UWord real_I;
      
-     ErtsCountBreak((Uint *) I, &real_I);
+     ErtsCountBreak((UWord *) I, &real_I);
      ASSERT(VALID_INSTR(real_I));
      Goto(real_I);
  }
 
  OpCase(i_trace_breakpoint):
      if (! IS_TRACED_FL(c_p, F_TRACE_CALLS)) {
-	 Uint real_I;
+	 UWord real_I;
 	 
-	 ErtsBreakSkip((Uint *) I, &real_I);
+	 ErtsBreakSkip((UWord *) I, &real_I);
 	 Goto(real_I);
      }
  /* Fall through to next case */
@@ -4355,11 +4374,10 @@ apply_bif_or_nif_epilogue:
      SWAPOUT;
      reg[0] = r(0);
 
-     if (*cp_val((Eterm)c_p->cp) 
-	 == (Uint) OpCode(return_trace)) {
+     if (*(c_p->cp) == (UWord) OpCode(return_trace)) {
 	 cpp = (Uint*)&E[2];
-     } else if (*cp_val((Eterm)c_p->cp) 
-		== (Uint) OpCode(i_return_to_trace)) {
+     } else if (*(c_p->cp)
+		== (UWord) OpCode(i_return_to_trace)) {
 	 return_to_trace = !0;
 	 cpp = (Uint*)&E[0];
      } else {
@@ -4370,19 +4388,19 @@ apply_bif_or_nif_epilogue:
 	  * return_trace and/or i_return_to_trace stackframes
 	  * on the stack, they are not intermixed with y registers
 	  */
-	 Eterm *cp_save = c_p->cp;
+	 UWord *cp_save = c_p->cp;
 	 for (;;) {
 	     ASSERT(is_CP(*cpp));
-	     if (*cp_val(*cpp) == (Uint) OpCode(return_trace)) {
+	     if (*cp_val(*cpp) == (UWord) OpCode(return_trace)) {
 		 cpp += 3;
-	     } else if (*cp_val(*cpp) == (Uint) OpCode(i_return_to_trace)) {
+	     } else if (*cp_val(*cpp) == (UWord) OpCode(i_return_to_trace)) {
 		 return_to_trace = !0;
 		 cpp += 1;
 	     } else
 		 break;
 	 }
-	 c_p->cp = (Eterm *) *cpp;
-	 ASSERT(is_CP((Eterm)c_p->cp));
+	 c_p->cp = (UWord *) cp_val(*cpp);
+	 ASSERT(is_CP(*cpp));
 	 ERTS_SMP_UNREQ_PROC_MAIN_LOCK(c_p);
 	 real_I = erts_trace_break(c_p, I, reg, &flags, &tracer_pid);
 	 ERTS_SMP_REQ_PROC_MAIN_LOCK(c_p);
@@ -4418,12 +4436,12 @@ apply_bif_or_nif_epilogue:
 	 E -= 1;
 	 ASSERT(c_p->htop <= E && E <= c_p->hend);
 	 E[0] = make_cp(c_p->cp);
-	 c_p->cp = (Eterm *) make_cp(beam_return_to_trace);
+	 c_p->cp = (UWord *) beam_return_to_trace;
      }
      if (flags & MATCH_SET_RX_TRACE) {
 	 E -= 3;
 	 ASSERT(c_p->htop <= E && E <= c_p->hend);
-	 ASSERT(is_CP((Eterm) (I - 3)));
+	 ASSERT(is_CP((Eterm) (UWord) (I - 3)));
 	 ASSERT(am_true == tracer_pid || 
 		is_internal_pid(tracer_pid) || is_internal_port(tracer_pid));
 	 E[2] = make_cp(c_p->cp);
@@ -4431,9 +4449,9 @@ apply_bif_or_nif_epilogue:
 	 E[0] = make_cp(I - 3); /* We ARE at the beginning of an 
 				   instruction,
 				   the funcinfo is above i. */
-	 c_p->cp = (Eterm*)
-	     make_cp(flags & MATCH_SET_EXCEPTION_TRACE
-		     ? beam_exception_trace : beam_return_trace);
+	 c_p->cp =
+	     (flags & MATCH_SET_EXCEPTION_TRACE)
+		     ? beam_exception_trace : beam_return_trace;
 	 erts_smp_proc_lock(c_p, ERTS_PROC_LOCKS_ALL_MINOR);
 	 c_p->trace_flags |= F_EXCEPTION_TRACE;
 	 erts_smp_proc_unlock(c_p, ERTS_PROC_LOCKS_ALL_MINOR);
@@ -4446,10 +4464,10 @@ apply_bif_or_nif_epilogue:
 	 Uint *cpp = (Uint*) E;
 	 for(;;) {
 	     ASSERT(is_CP(*cpp));
-	     if (*cp_val(*cpp) == (Uint) OpCode(return_trace)) {
+	     if (*cp_val(*cpp) == (UWord) OpCode(return_trace)) {
 		 do ++cpp; while(is_not_CP(*cpp));
 		 cpp += 2;
-	     } else if (*cp_val(*cpp) == (Uint) OpCode(i_return_to_trace)) {
+	     } else if (*cp_val(*cpp) == (UWord) OpCode(i_return_to_trace)) {
 		 do ++cpp; while(is_not_CP(*cpp));
 	     } else break;
 	 }
@@ -4460,7 +4478,7 @@ apply_bif_or_nif_epilogue:
 	 SWAPIN;
      }
      c_p->cp = NULL;
-     SET_I((Eterm *) E[0]);
+     SET_I((UWord *) cp_val(E[0]));
      E += 1;
      Goto(*I);
  }
@@ -4471,7 +4489,7 @@ apply_bif_or_nif_epilogue:
 
  OpCase(i_global_cons):
  {
-     Eterm *next;
+     UWord *next;
 #ifdef HYBRID
      Eterm *hp;
 
@@ -4493,7 +4511,7 @@ apply_bif_or_nif_epilogue:
 
  OpCase(i_global_tuple):
  {
-     Eterm *next;
+     UWord *next;
      int len;
 #ifdef HYBRID
      Eterm list;
@@ -4528,7 +4546,7 @@ apply_bif_or_nif_epilogue:
 
  OpCase(i_global_copy):
  {
-     Eterm *next;
+     UWord *next;
      PreFetch(0,next);
 #ifdef HYBRID
      if (!IS_CONST(r(0)))
@@ -4557,7 +4575,7 @@ apply_bif_or_nif_epilogue:
 
  OpCase(fmove_ql): {
      Eterm fr = Arg(1);
-     Eterm* next;
+     UWord *next;
 
      PreFetch(2, next);
      GET_DOUBLE(Arg(0), *(FloatDef*)ADD_BYTE_OFFSET(freg, fr));
@@ -4567,7 +4585,7 @@ apply_bif_or_nif_epilogue:
  OpCase(fmove_dl): {
      Eterm targ1;
      Eterm fr = Arg(1);
-     Eterm* next;
+     UWord *next;
 
      PreFetch(2, next);
      GetR(0, targ1);
@@ -4588,7 +4606,7 @@ apply_bif_or_nif_epilogue:
  OpCase(fconv_dl): {
      Eterm targ1;
      Eterm fr = Arg(1);
-     Eterm* next;
+     UWord *next;
 
      GetR(0, targ1);
      PreFetch(2, next);
@@ -4617,7 +4635,7 @@ apply_bif_or_nif_epilogue:
 	 erl_exit(1, "fclearerror/i_fcheckerror without fpe signals (beam_emu)");
 #else
      OpCase(fclearerror): {
-	 Eterm* next;
+	 UWord *next;
 
 	 PreFetch(0, next);
 	 ERTS_FP_CHECK_INIT(c_p);
@@ -4625,7 +4643,7 @@ apply_bif_or_nif_epilogue:
      }
 
      OpCase(i_fcheckerror): {
-	 Eterm* next;
+	 UWord *next;
 
 	 PreFetch(0, next);
 	 ERTS_FP_ERROR(c_p, freg[0].fd, goto fbadarith);
@@ -4639,7 +4657,7 @@ apply_bif_or_nif_epilogue:
 
 
  OpCase(i_fadd_lll): {
-     Eterm* next;
+     UWord *next;
 
      PreFetch(3, next);
      ERTS_FP_CHECK_INIT(c_p);
@@ -4648,7 +4666,7 @@ apply_bif_or_nif_epilogue:
      NextPF(3, next);
  }
  OpCase(i_fsub_lll): {
-     Eterm* next;
+     UWord *next;
 
      PreFetch(3, next);
      ERTS_FP_CHECK_INIT(c_p);
@@ -4657,7 +4675,7 @@ apply_bif_or_nif_epilogue:
      NextPF(3, next);
  }
  OpCase(i_fmul_lll): {
-     Eterm* next;
+     UWord *next;
 
      PreFetch(3, next);
      ERTS_FP_CHECK_INIT(c_p);
@@ -4666,7 +4684,7 @@ apply_bif_or_nif_epilogue:
      NextPF(3, next);
  }
  OpCase(i_fdiv_lll): {
-     Eterm* next;
+     UWord *next;
 
      PreFetch(3, next);
      ERTS_FP_CHECK_INIT(c_p);
@@ -4675,7 +4693,7 @@ apply_bif_or_nif_epilogue:
      NextPF(3, next);
  }
  OpCase(i_fnegate_ll): {
-     Eterm* next;
+     UWord *next;
 
      PreFetch(2, next);
      ERTS_FP_CHECK_INIT(c_p);
@@ -4742,7 +4760,7 @@ apply_bif_or_nif_epilogue:
      neg_o_reds = -c_p->def_arg_reg[4];
      FCALLS = c_p->fcalls;
      SWAPIN;
-     switch( c_p->def_arg_reg[3] ) {
+     switch( c_p->def_arg_reg[3] ) { /* XXX:PaN - Halfword wont work with hipe yet... */
        case HIPE_MODE_SWITCH_RES_RETURN:
 	 ASSERT(is_value(reg[0]));
 	 MoveReturn(reg[0], r(0));
@@ -4754,7 +4772,7 @@ apply_bif_or_nif_epilogue:
 	 /* This can be used to call any function value, but currently it's
 	    only used to call closures referring to unloaded modules. */
 	 {
-	     Eterm *next;
+	     UWord *next;
 
 	     next = call_fun(c_p, c_p->arity - 1, reg, THE_NON_VALUE);
 	     SWAPIN;
@@ -4903,8 +4921,8 @@ apply_bif_or_nif_epilogue:
 			      bif_table[i].name,
 			      bif_table[i].arity);
 	 bif_export[i] = ep;
-	 ep->code[3] = (Eterm) OpCode(apply_bif);
-	 ep->code[4] = (Eterm) bif_table[i].f;
+	 ep->code[3] = (UWord) OpCode(apply_bif);
+	 ep->code[4] = (UWord) bif_table[i].f;
      }
 
      return;
@@ -5007,8 +5025,8 @@ Eterm error_atom[NUMBER_EXIT_CODES] = {
  * at the point of the original exception.
  */
 
-static Eterm*
-handle_error(Process* c_p, Eterm* pc, Eterm* reg, BifFunction bf)
+static UWord*
+handle_error(Process* c_p, UWord* pc, Eterm* reg, BifFunction bf)
 {
     Eterm* hp;
     Eterm Value = c_p->fvalue;
@@ -5062,7 +5080,7 @@ handle_error(Process* c_p, Eterm* pc, Eterm* reg, BifFunction bf)
     /* Find a handler or die */
     if ((c_p->catches > 0 || IS_TRACED_FL(c_p, F_EXCEPTION_TRACE))
 	&& !(c_p->freason & EXF_PANIC)) {
-	Eterm *new_pc;
+	UWord *new_pc;
         /* The Beam handler code (catch_end or try_end) checks reg[0]
 	   for THE_NON_VALUE to see if the previous code finished
 	   abnormally. If so, reg[1], reg[2] and reg[3] should hold the
@@ -5088,13 +5106,13 @@ handle_error(Process* c_p, Eterm* pc, Eterm* reg, BifFunction bf)
 /*
  * Find the nearest catch handler
  */
-static Eterm*
+static UWord*
 next_catch(Process* c_p, Eterm *reg) {
     int active_catches = c_p->catches > 0;
     int have_return_to_trace = 0;
     Eterm *ptr, *prev, *return_to_trace_ptr = NULL;
-    Uint i_return_trace = beam_return_trace[0];
-    Uint i_return_to_trace = beam_return_to_trace[0];
+    UWord i_return_trace = beam_return_trace[0];
+    UWord i_return_to_trace = beam_return_to_trace[0];
     ptr = prev = c_p->stop;
     ASSERT(is_CP(*ptr));
     ASSERT(ptr <= STACK_START(c_p));
@@ -5103,9 +5121,9 @@ next_catch(Process* c_p, Eterm *reg) {
 			     *cp_val(*ptr) != i_return_to_trace))
 	&& c_p->cp) {
 	/* Can not follow cp here - code may be unloaded */
-	Uint *cpp = cp_val((Eterm) c_p->cp);
+	UWord *cpp = c_p->cp;
 	if (cpp == beam_exception_trace) {
-	    erts_trace_exception(c_p, (Eterm*) ptr[0],
+	    erts_trace_exception(c_p, cp_val(ptr[0]),
 				 reg[1], reg[2], ptr+1);
 	    /* Skip return_trace parameters */
 	    ptr += 2;
@@ -5129,7 +5147,7 @@ next_catch(Process* c_p, Eterm *reg) {
 		    if (is_catch(*ptr) && active_catches) goto found_catch;
 		}
 		if (cp_val(*prev) == beam_exception_trace) {
-		    erts_trace_exception(c_p, (Eterm*) ptr[0],
+		    erts_trace_exception(c_p, cp_val(ptr[0]),
 					 reg[1], reg[2], ptr+1);
 		}
 		/* Skip return_trace parameters */
@@ -5258,7 +5276,7 @@ expand_error_value(Process* c_p, Uint freason, Eterm Value) {
  */
 
 static void
-save_stacktrace(Process* c_p, Eterm* pc, Eterm* reg, BifFunction bf,
+save_stacktrace(Process* c_p, UWord* pc, Eterm* reg, BifFunction bf,
 		Eterm args) {
     struct StackTrace* s;
     int sz;
@@ -5269,7 +5287,7 @@ save_stacktrace(Process* c_p, Eterm* pc, Eterm* reg, BifFunction bf,
     }
 
     /* Create a container for the exception data */
-    sz = (offsetof(struct StackTrace, trace) + sizeof(Eterm)*depth
+    sz = (offsetof(struct StackTrace, trace) + sizeof(UWord *)*depth
           + sizeof(Eterm) - 1) / sizeof(Eterm);
     s = (struct StackTrace *) HAlloc(c_p, 1 + sz);
     /* The following fields are inside the bignum */
@@ -5356,9 +5374,10 @@ save_stacktrace(Process* c_p, Eterm* pc, Eterm* reg, BifFunction bf,
 
     /* Save the actual stack trace */
     if (depth > 0) {
-	Eterm *ptr, *prev = s->depth ? s->trace[s->depth-1] : NULL;
-	Uint i_return_trace = beam_return_trace[0];
-	Uint i_return_to_trace = beam_return_to_trace[0];
+	Eterm *ptr;
+	UWord *prev = s->depth ? s->trace[s->depth-1] : NULL;
+	UWord i_return_trace = beam_return_trace[0];
+	UWord i_return_to_trace = beam_return_to_trace[0];
 	/*
 	 * Traverse the stack backwards and add all unique continuation
 	 * pointers to the buffer, up to the maximum stack trace size.
@@ -5371,7 +5390,7 @@ save_stacktrace(Process* c_p, Eterm* pc, Eterm* reg, BifFunction bf,
 				   *cp_val(*ptr) != i_return_to_trace))
 	    && c_p->cp) {
 	    /* Can not follow cp here - code may be unloaded */
-	    Uint *cpp = cp_val((Eterm) c_p->cp);
+	    UWord *cpp = c_p->cp;
 	    if (cpp == beam_exception_trace || cpp == beam_return_trace) {
 		/* Skip return_trace parameters */
 		ptr += 2;
@@ -5391,7 +5410,7 @@ save_stacktrace(Process* c_p, Eterm* pc, Eterm* reg, BifFunction bf,
 		    /* Skip stack frame variables */
 		    do ++ptr; while (is_not_CP(*ptr));
 		} else {
-		    Eterm *cp = (Eterm *)(*ptr);
+		    UWord *cp = cp_val(*ptr);
 		    if (cp != prev) {
 			/* Record non-duplicates only */
 			prev = cp;
@@ -5463,9 +5482,12 @@ build_stacktrace(Process* c_p, Eterm exc) {
     struct StackTrace* s;
     Eterm  args;
     int    depth;
-    Eterm* current;
+    UWord* current;
+#if HALFWORD_HEAP
+    UWord current_buff[3];
+#endif
     Eterm  Where = NIL;
-    Eterm* next_p = &Where;
+    Eterm *next_p = &Where;
 
     if (! (s = get_trace_from_exc(exc))) {
         return NIL;
@@ -5493,7 +5515,14 @@ build_stacktrace(Process* c_p, Eterm exc) {
      * (e.g. spawn_link(erlang, abs, [1])).
      */
     if (current == NULL) {
+#if HALFWORD_HEAP
+	current = current_buff;
+	current[0] = (UWord) c_p->initial[0];
+	current[1] = (UWord) c_p->initial[1];
+	current[2] = (UWord) c_p->initial[2];
+#else
 	current = c_p->initial;
+#endif
 	args = am_true; /* Just in case */
     } else {
 	args = get_args_from_exc(exc);
@@ -5529,7 +5558,7 @@ build_stacktrace(Process* c_p, Eterm exc) {
 	 * Finally, we go through the saved continuation pointers.
 	 */
 	for (i = 0; i < depth; i++) {
-	    Eterm *fi = find_function_from_pc((Eterm *) s->trace[i]);
+	    UWord *fi = find_function_from_pc((UWord *) s->trace[i]);
 	    if (fi == NULL) continue;
 	    mfa = TUPLE3(hp, fi[0], fi[1], make_small(fi[2]));
 	    hp += 4;
@@ -5546,7 +5575,7 @@ build_stacktrace(Process* c_p, Eterm exc) {
 
 
 static Eterm
-call_error_handler(Process* p, Eterm* fi, Eterm* reg)
+call_error_handler(Process* p, UWord* fi, Eterm* reg)
 {
     Eterm* hp;
     Export* ep;
@@ -5594,7 +5623,7 @@ call_error_handler(Process* p, Eterm* fi, Eterm* reg)
 }
 
 static Eterm
-call_breakpoint_handler(Process* p, Eterm* fi, Eterm* reg)
+call_breakpoint_handler(Process* p, UWord* fi, Eterm* reg)
 {
     Eterm* hp;
     Export* ep;
@@ -5687,7 +5716,7 @@ apply_setup_error_handler(Process* p, Eterm module, Eterm function, Uint arity,
     return ep;
 }
 
-static Uint*
+static UWord*
 apply(Process* p, Eterm module, Eterm function, Eterm args, Eterm* reg)
 {
     int arity;
@@ -5769,7 +5798,7 @@ apply(Process* p, Eterm module, Eterm function, Eterm args, Eterm* reg)
     return ep->address;
 }
 
-static Uint*
+static UWord*
 fixed_apply(Process* p, Eterm* reg, Uint arity)
 {
     Export* ep;
@@ -5875,7 +5904,7 @@ hibernate(Process* c_p, Eterm module, Eterm function, Eterm args, Eterm* reg)
     c_p->stop = STACK_START(c_p);
     c_p->catches = 0;
     c_p->i = beam_apply;
-    c_p->cp = (Eterm *) beam_apply+1;
+    c_p->cp = (UWord *) beam_apply+1;
 
     /*
      * If there are no waiting messages, garbage collect and
@@ -5905,7 +5934,7 @@ hibernate(Process* c_p, Eterm module, Eterm function, Eterm args, Eterm* reg)
     return 1;
 }
 
-static Uint*
+static UWord*
 call_fun(Process* p,		/* Current process. */
 	 int arity,		/* Number of arguments for Fun. */
 	 Eterm* reg,		/* Contents of registers. */
@@ -5925,7 +5954,7 @@ call_fun(Process* p,		/* Current process. */
     if (is_fun_header(hdr)) {
 	ErlFunThing* funp = (ErlFunThing *) fun_val(fun);
 	ErlFunEntry* fe;
-	Eterm* code_ptr;
+	UWord* code_ptr;
 	Eterm* var_ptr;
 	int actual_arity;
 	unsigned num_free;
@@ -6020,7 +6049,7 @@ call_fun(Process* p,		/* Current process. */
 	    }
 	}
     } else if (is_export_header(hdr)) {
-	Export* ep = (Export *) (export_val(fun))[1];
+	Export* ep = *((Export **) (export_val(fun) + 1));
 	int actual_arity = (int) ep->code[2];
 	if (arity == actual_arity) {
 	    return ep->address;
@@ -6088,7 +6117,7 @@ call_fun(Process* p,		/* Current process. */
     }
 }
 
-static Eterm*
+static UWord*
 apply_fun(Process* p, Eterm fun, Eterm args, Eterm* reg)
 {
     int arity;
@@ -6182,7 +6211,7 @@ erts_is_builtin(Eterm Mod, Eterm Name, int arity)
     if ((ep = export_get(&e)) == NULL) {
 	return 0;
     }
-    return ep->address == ep->code+3 && (ep->code[3] == (Uint) em_apply_bif);
+    return ep->address == ep->code+3 && (ep->code[3] == (UWord) em_apply_bif);
 }