Index: generic/tclAlloc.c
===================================================================
RCS file: /cvsroot/tcl/tcl/generic/tclAlloc.c,v
retrieving revision 1.26
diff -u -r1.26 tclAlloc.c
--- generic/tclAlloc.c	13 Dec 2007 15:23:14 -0000	1.26
+++ generic/tclAlloc.c	17 Dec 2007 13:43:11 -0000
@@ -44,16 +44,6 @@
 #endif
 
 /*
- * Alignment for allocated memory.
- */
-
-#if defined(__APPLE__)
-#define ALLOCALIGN	16
-#else
-#define ALLOCALIGN	8
-#endif
-
-/*
  * The overhead on a block is at least 8 bytes. When free, this space contains
  * a pointer to the next free block, and the bottom two bits must be zero.
  * When in use, the first byte is set to MAGIC, and the second byte is the
@@ -66,7 +56,7 @@
 
 union overhead {
     union overhead *next;		/* when free */
-    unsigned char padding[ALLOCALIGN];	/* align struct to ALLOCALIGN bytes */
+    unsigned char padding[TCL_ALLOCALIGN];	/* align struct to TCL_ALLOCALIGN bytes */
     struct {
 	unsigned char magic0;		/* magic number */
 	unsigned char index;		/* bucket # */
@@ -110,7 +100,7 @@
  * precedes the data area returned to the user.
  */
 
-#define MINBLOCK	((sizeof(union overhead) + (ALLOCALIGN-1)) & ~(ALLOCALIGN-1))
+#define MINBLOCK	((sizeof(union overhead) + (TCL_ALLOCALIGN-1)) & ~(TCL_ALLOCALIGN-1))
 #define NBUCKETS	(13 - (MINBLOCK >> 4))
 #define MAXMALLOC	(1<<(NBUCKETS+2))
 static union overhead *nextf[NBUCKETS];
Index: generic/tclExecute.c
===================================================================
RCS file: /cvsroot/tcl/tcl/generic/tclExecute.c,v
retrieving revision 1.357
diff -u -r1.357 tclExecute.c
--- generic/tclExecute.c	13 Dec 2007 15:23:16 -0000	1.357
+++ generic/tclExecute.c	17 Dec 2007 13:43:12 -0000
@@ -836,6 +836,36 @@
 }
 
 /*
+ * Auxiliary code to insure that GrowEvaluationStack always returns correctly 
+ * aligned memory. This assumes that TCL_ALLOCALIGN is a multiple of the
+ * wordsize 'sizeof(Tcl_Obj *)'. 
+ */
+
+#define WALLOCALIGN \
+    (TCL_ALLOCALIGN/sizeof(Tcl_Obj *))
+
+static inline int
+OFFSET(
+    Tcl_Obj **markerPtr)
+{
+    /*
+     * Note that we are only interested in the low bits of the address, so
+     * that the fact that PTR2INT may lose the high bits is irrelevant.
+     */
+
+    int mask, base, new;
+
+    mask = WALLOCALIGN-1;
+    base = (PTR2INT(markerPtr) & mask);
+    new  = (base + 1 + mask) & ~mask;
+    return (new - base);
+}
+
+#define MEMSTART(markerPtr) \
+    ((markerPtr) + OFFSET(markerPtr))
+
+
+/*
  *----------------------------------------------------------------------
  *
  * GrowEvaluationStack --
@@ -865,36 +895,44 @@
     ExecStack *esPtr = eePtr->execStackPtr, *oldPtr = NULL;
     int newBytes, newElems, currElems;
     int needed = growth - (esPtr->endPtr - esPtr->tosPtr);
-    Tcl_Obj **markerPtr = esPtr->markerPtr;
+    Tcl_Obj **markerPtr = esPtr->markerPtr, **memStart;
 
     if (move) {
 	if (!markerPtr) {
 	    Tcl_Panic("STACK: Reallocating with no previous alloc");
 	}
 	if (needed <= 0) {
-	    return markerPtr + 1;
+	    return MEMSTART(markerPtr);
 	}
-    } else if (needed < 0) {
-	/*
-	 * Put a marker pointing to the previous marker in this stack, and
-	 * store it in esPtr as the current marker. Return a pointer to one
-	 * word past the marker.
-	 */
+    } else {
+	Tcl_Obj **tmpMarkerPtr = esPtr->tosPtr + 1;
+	int offset = OFFSET(tmpMarkerPtr);
 
-	esPtr->markerPtr = ++esPtr->tosPtr;
-	*esPtr->markerPtr = (Tcl_Obj *) markerPtr;
-	return esPtr->markerPtr + 1;
+	if (needed + offset < 0) {
+	    /*
+	     * Put a marker pointing to the previous marker in this stack, and 
+	     * store it in esPtr as the current marker. Return a pointer to
+	     * the start of aligned memory.
+	     */
+
+	    esPtr->markerPtr = tmpMarkerPtr;
+	    memStart = tmpMarkerPtr + offset; 
+	    esPtr->tosPtr = memStart - 1;
+	    *esPtr->markerPtr = (Tcl_Obj *) markerPtr;
+	    return memStart;
+	}
     }
 
     /*
      * Reset move to hold the number of words to be moved to new stack (if
-     * any) and growth to hold the complete stack requirements.
+     * any) and growth to hold the complete stack requirements: add the marker
+     * and maximal possible offset. 
      */
 
     if (move) {
-	move = esPtr->tosPtr - markerPtr;
+	move = esPtr->tosPtr - MEMSTART(markerPtr) + 1;
     }
-    needed = growth + move + 1; /* Add the marker. */
+    needed = growth + move + WALLOCALIGN - 1;
 
     /*
      * Check if there is enough room in the next stack (if there is one, it
@@ -949,10 +987,12 @@
      */
 
     esPtr->stackWords[0] = NULL;
-    esPtr->markerPtr = esPtr->tosPtr = &esPtr->stackWords[0];
-
+    esPtr->markerPtr = &esPtr->stackWords[0];
+    memStart = MEMSTART(esPtr->markerPtr);
+    esPtr->tosPtr = memStart - 1;
+    
     if (move) {
-	memcpy(&esPtr->stackWords[1], (markerPtr+1), move*sizeof(Tcl_Obj *));
+	memcpy(memStart, MEMSTART(markerPtr), move*sizeof(Tcl_Obj *));
 	esPtr->tosPtr += move;
 	oldPtr->markerPtr = (Tcl_Obj **) *markerPtr;
 	oldPtr->tosPtr = markerPtr-1;
@@ -966,7 +1006,7 @@
 	DeleteExecStack(oldPtr);
     }
 
-    return &esPtr->stackWords[1];
+    return memStart;
 }
 
 /*
@@ -1043,7 +1083,7 @@
     esPtr = eePtr->execStackPtr;
     markerPtr = esPtr->markerPtr;
 
-    if ((markerPtr+1) != (Tcl_Obj **)freePtr) {
+    if (MEMSTART(markerPtr) != (Tcl_Obj **)freePtr) {
 	Tcl_Panic("TclStackFree: incorrect freePtr. Call out of sequence?");
     }
 
@@ -1104,7 +1144,7 @@
     esPtr = eePtr->execStackPtr;
     markerPtr = esPtr->markerPtr;
 
-    if ((markerPtr+1) != (Tcl_Obj **)ptr) {
+    if (MEMSTART(markerPtr) != (Tcl_Obj **)ptr) {
 	Tcl_Panic("TclStackRealloc: incorrect ptr. Call out of sequence?");
     }
 
Index: generic/tclInt.h
===================================================================
RCS file: /cvsroot/tcl/tcl/generic/tclInt.h,v
retrieving revision 1.358
diff -u -r1.358 tclInt.h
--- generic/tclInt.h	13 Dec 2007 15:23:18 -0000	1.358
+++ generic/tclInt.h	17 Dec 2007 13:43:13 -0000
@@ -2034,6 +2034,17 @@
 #define UCHAR(c) ((unsigned char) (c))
 
 /*
+ * This macro is used to properly align the memory allocated by Tcl, giving
+ * the same alignment as the native malloc
+ */
+
+#if defined(__APPLE__)
+#define TCL_ALLOCALIGN	16
+#else
+#define TCL_ALLOCALIGN	(2*sizeof(void *))
+#endif
+
+/*
  * This macro is used to determine the offset needed to safely allocate any
  * data structure in memory. Given a starting offset or size, it "rounds up"
  * or "aligns" the offset to the next 8-byte boundary so that any data
Index: generic/tclThreadAlloc.c
===================================================================
RCS file: /cvsroot/tcl/tcl/generic/tclThreadAlloc.c,v
retrieving revision 1.24
diff -u -r1.24 tclThreadAlloc.c
--- generic/tclThreadAlloc.c	13 Dec 2007 15:23:20 -0000	1.24
+++ generic/tclThreadAlloc.c	17 Dec 2007 13:43:14 -0000
@@ -40,16 +40,6 @@
 #define NOBJHIGH	1200
 
 /*
- * Alignment for allocated memory.
- */
-
-#if defined(__APPLE__)
-#define ALLOCALIGN	16
-#else
-#define ALLOCALIGN	8
-#endif
-
-/*
  * The following union stores accounting information for each block including
  * two small magic numbers and a bucket number when in use or a next pointer
  * when free. The original requested size (not including the Block overhead)
@@ -69,7 +59,7 @@
 	} u;
 	size_t reqSize;			/* Requested allocation size. */
     } b;
-    unsigned char padding[ALLOCALIGN];
+    unsigned char padding[TCL_ALLOCALIGN];
 } Block;
 #define nextBlock	b.u.next
 #define sourceBucket	b.u.s.bucket
@@ -83,7 +73,7 @@
  * of buckets in the bucket cache.
  */
 
-#define MINALLOC	((sizeof(Block) + 8 + (ALLOCALIGN-1)) & ~(ALLOCALIGN-1))
+#define MINALLOC	((sizeof(Block) + 8 + (TCL_ALLOCALIGN-1)) & ~(TCL_ALLOCALIGN-1))
 #define NBUCKETS	(11 - (MINALLOC >> 5))
 #define MAXALLOC	(MINALLOC << (NBUCKETS - 1))
 
