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, 9 insertions, 2 deletions

diff --git a/erts/emulator/beam/big.h b/erts/emulator/beam/big.h
index b8e38d482c..d74da7cef7 100644
--- a/erts/emulator/beam/big.h
+++ b/erts/emulator/beam/big.h
@@ -34,7 +34,7 @@
 
 typedef Uint     ErtsDigit;
 
-#if (SIZEOF_VOID_P == 4) && defined(SIZEOF_LONG_LONG) && (SIZEOF_LONG_LONG == 8)
+#if ((SIZEOF_VOID_P == 4) || HALFWORD_HEAP) && defined(SIZEOF_LONG_LONG) && (SIZEOF_LONG_LONG == 8)
 /* Assume 32-bit machine with long long support */
 typedef Uint64   ErtsDoubleDigit;
 typedef Uint16   ErtsHalfDigit;
@@ -58,7 +58,7 @@ typedef Uint32   ErtsHalfDigit;
 
 typedef Uint  dsize_t;	 /* Vector size type */
 
-#define D_EXP (SIZEOF_VOID_P*8)
+#define D_EXP (ERTS_SIZEOF_ETERM*8)
 #define D_MASK     ((ErtsDigit)(-1))      /* D_BASE-1 */
 
 /* macros for bignum objects */
@@ -88,6 +88,12 @@ typedef Uint  dsize_t;	 /* Vector size type */
 
 #define BIG_UINT_HEAP_SIZE (1 + 1)	/* always, since sizeof(Uint) <= sizeof(Eterm) */
 
+#if HALFWORD_HEAP
+#define BIG_UWORD_HEAP_SIZE(UW) (((UW) >> (sizeof(Uint) * 8)) ? 3 : 2)
+#else
+#define BIG_UWORD_HEAP_SIZE(UW) BIG_UINT_HEAP_SIZE
+#endif
+
 #ifdef ARCH_32
 
 #define ERTS_UINT64_BIG_HEAP_SIZE__(X) \
@@ -136,6 +142,7 @@ int big_ucomp (Eterm, Eterm);
 int big_to_double(Eterm x, double* resp);
 Eterm small_to_big(Sint, Eterm*);
 Eterm uint_to_big(Uint, Eterm*);
+Eterm uword_to_big(UWord, Eterm*);
 Eterm erts_make_integer(Uint, Process *);
 
 dsize_t big_bytes(Eterm);