lix/externals/aterm-aliasing.patch

diff -rc aterm-1142707243.10633/aterm/aterm.c aterm/aterm/aterm.c
*** aterm-1142707243.10633/aterm/aterm.c	2006-02-08 11:35:28.000000000 +0100
--- aterm/aterm/aterm.c	2006-04-25 17:10:52.000000000 +0200
***************
*** 193,198 ****
--- 193,199 ----
    /* that have char == 2 bytes, and sizeof(header_type) == 2 */
    assert(sizeof(header_type) == sizeof(ATerm *));
    assert(sizeof(header_type) >= 4);
+   assert(sizeof(ATerm) == sizeof(MachineWord));
  
    /*}}}  */
    /*{{{  Initialize buffer */
diff -rc aterm-1142707243.10633/aterm/memory.c aterm/aterm/memory.c
*** aterm-1142707243.10633/aterm/memory.c	2006-03-09 15:02:56.000000000 +0100
--- aterm/aterm/memory.c	2006-04-25 18:22:00.000000000 +0200
***************
*** 119,130 ****
                          hash_number(tmp,3)) 
  */
  
  #define HASHNUMBER3(t)\
! FINISH(COMBINE(START(((MachineWord*)t)[0]), ((MachineWord*)t)[2]))
  
  #define HASHNUMBER4(t)\
! FINISH(COMBINE(COMBINE(START(((MachineWord*)t)[0]), \
! 		       ((MachineWord*)t)[2]),((MachineWord*)t)[3]))
  
  #define HASHINT(val) \
  FINISH(COMBINE(START( (AT_INT<<SHIFT_TYPE) ), val))
--- 119,171 ----
                          hash_number(tmp,3)) 
  */
  
+ /* The ATerm library use some heavy aliasing.  For instance, the
+    various ATermXXX structures are referenced through MachineWord
+    arrays.  This is not generally allowed by the C standard --- see
+    C99, section 6.5, clause 7.  In particular, this means that you
+    cannot assign something through an ATermXXX pointer, e.g.,
+ 
+      protoAppl->header = header;
+ 
+    and then read it through a MachineWord*, e.g.,
+ 
+      hnr = hash_number((ATerm) protoAppl, 2);
+ 
+    (hash_number walks over the term by casting it to a MachineWord*).
+ 
+    However, the same clause of the C standard also specifies that you
+    *can* read the memory location through a union type that contains
+    both the original type (e.g. ATermAppl) and the type used to read
+    the memory location (e.g. MachineWord).  That's what we do
+    below: we have a union of all the types that occur in the various
+    ATerm types.  We then read the "w" element of the union.  The
+    compiler is not allowed to assume absence of aliasing with the
+    other types in the union.
+ 
+    A better solution would be to hash the term through a character
+    pointer (since *any* memory location can be legally read as a
+    character), but I'm too lazy right now.  Performance might also
+    suffer if we do that. */
+ 
+ typedef union 
+ {
+     MachineWord w;
+     header_type header;
+     ATerm term;
+     ATermList list;
+     int i;
+     double d;
+     void* p;
+ } Aliaser;
+ 
+ #define GET_WORD(t, n) (((Aliaser*) (((MachineWord*) t) + n))->w)
+ 
  #define HASHNUMBER3(t)\
! FINISH(COMBINE(START(GET_WORD(t, 0)), GET_WORD(t, 2)))
  
  #define HASHNUMBER4(t)\
! FINISH(COMBINE(COMBINE(START(GET_WORD(t, 0)), \
! 		       GET_WORD(t, 2)), GET_WORD(t, 3)))
  
  #define HASHINT(val) \
  FINISH(COMBINE(START( (AT_INT<<SHIFT_TYPE) ), val))
***************
*** 132,144 ****
  
  #endif /* HASHPEM */
  
! #define PROTO_APPL_ARGS ((ATerm *) (protoTerm + ARG_OFFSET))
  
  #define SET_PROTO_APPL_ARG(i, a) \
!   (PROTO_APPL_ARGS[(i)] = (a))
  
  #define GET_PROTO_APPL_ARG(i) \
!   (PROTO_APPL_ARGS[(i)])
  
  #define CHECK_TERM(t) \
    assert((t) != NULL \
--- 173,185 ----
  
  #endif /* HASHPEM */
  
! #define PROTO_APPL_ARGS (protoTerm + ARG_OFFSET)
  
  #define SET_PROTO_APPL_ARG(i, a) \
!   (PROTO_APPL_ARGS[(i)] = (MachineWord) (a))
  
  #define GET_PROTO_APPL_ARG(i) \
!   ((ATerm) PROTO_APPL_ARGS[(i)])
  
  #define CHECK_TERM(t) \
    assert((t) != NULL \
***************
*** 323,336 ****
  #else
  static HashNumber hash_number(ATerm t, int size)
  {
-   MachineWord *words = (MachineWord *) t;
    int i;
    HashNumber hnr;
  
!   hnr = START(HIDE_AGE_MARK(words[0]));
    
    for (i=2; i<size; i++) {
!     hnr = COMBINE(hnr, words[i]);
    }
  
    return FINISH(hnr);
--- 364,376 ----
  #else
  static HashNumber hash_number(ATerm t, int size)
  {
    int i;
    HashNumber hnr;
  
!   hnr = START(HIDE_AGE_MARK(GET_WORD(t, 0)));
    
    for (i=2; i<size; i++) {
!     hnr = COMBINE(hnr, GET_WORD(t, i));
    }
  
    return FINISH(hnr);
***************
*** 338,351 ****
  
  static HashNumber hash_number_anno(ATerm t, int size, ATerm anno)
  {
-   MachineWord *words = (MachineWord *) t;
    int i;
    HashNumber hnr;
  
!   hnr = START(HIDE_AGE_MARK(words[0]));
    
    for (i=2; i<size; i++) {
!     hnr = COMBINE(hnr, words[i]);
    }
    hnr = COMBINE(hnr, (MachineWord)anno);
  
--- 378,390 ----
  
  static HashNumber hash_number_anno(ATerm t, int size, ATerm anno)
  {
    int i;
    HashNumber hnr;
  
!   hnr = START(HIDE_AGE_MARK(GET_WORD(t, 0)));
    
    for (i=2; i<size; i++) {
!     hnr = COMBINE(hnr, GET_WORD(t, i));
    }
    hnr = COMBINE(hnr, (MachineWord)anno);
  
***************
*** 1639,1645 ****
    protoAppl->header = header;
    CHECK_HEADER(protoAppl->header);
  
!   if (args != PROTO_APPL_ARGS) {
      for (i=0; i<arity; i++) {
        CHECK_TERM(args[i]);
        SET_PROTO_APPL_ARG(i, args[i]);
--- 1678,1684 ----
    protoAppl->header = header;
    CHECK_HEADER(protoAppl->header);
  
!   if (args != (ATerm *) PROTO_APPL_ARGS) {
      for (i=0; i<arity; i++) {
        CHECK_TERM(args[i]);
        SET_PROTO_APPL_ARG(i, args[i]);
***************
*** 1680,1686 ****
      hashtable[hnr] = cur;
    }
  
!   if (args != PROTO_APPL_ARGS) {
      for (i=0; i<arity; i++) {
        protected_buffer[i] = NULL;
      }
--- 1719,1725 ----
      hashtable[hnr] = cur;
    }
  
!   if (args != (ATerm *) PROTO_APPL_ARGS) {
      for (i=0; i<arity; i++) {
        protected_buffer[i] = NULL;
      }
***************
*** 2144,2150 ****
    }
    SET_PROTO_APPL_ARG(n, arg);
  
!   result = ATmakeApplArray(sym, PROTO_APPL_ARGS);
    annos = AT_getAnnotations((ATerm)appl);
    if (annos != NULL) {
      result = (ATermAppl)AT_setAnnotations((ATerm)result, annos);
--- 2183,2189 ----
    }
    SET_PROTO_APPL_ARG(n, arg);
  
!   result = ATmakeApplArray(sym, (ATerm *) PROTO_APPL_ARGS);
    annos = AT_getAnnotations((ATerm)appl);
    if (annos != NULL) {
      result = (ATermAppl)AT_setAnnotations((ATerm)result, annos);