Add some debug support code to try to catch future mistakes in the area of

input functions that include garbage bytes in their results.  Provide a
compile-time option RANDOMIZE_ALLOCATED_MEMORY to make palloc fill returned
blocks with variable contents.  This option also makes the parser perform
conversions of literal constants twice and compare the results, emitting a
WARNING if they don't match.  (This is the code I used to catch the input
function bugs fixed in the previous commit.)  For the moment, I've set it
to be activated automatically by --enable-cassert.

src/backend/parser/parse_type.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/parse_type.c,v 1.94 2008/01/01 19:45:51 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/parse_type.c,v 1.95 2008/04/11 22:54:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -22,6 +22,7 @@
 #include "parser/parse_type.h"
 #include "utils/array.h"
 #include "utils/builtins.h"
+#include "utils/datum.h"
 #include "utils/lsyscache.h"
 #include "utils/syscache.h"
 
@@ -485,13 +486,38 @@ typeTypeRelid(Type typ)
 Datum
 stringTypeDatum(Type tp, char *string, int32 atttypmod)
 {
-	Oid			typinput;
-	Oid			typioparam;
+	Form_pg_type typform = (Form_pg_type) GETSTRUCT(tp);
+	Oid			typinput = typform->typinput;
+	Oid			typioparam = getTypeIOParam(tp);
+	Datum		result;
 
-	typinput = ((Form_pg_type) GETSTRUCT(tp))->typinput;
-	typioparam = getTypeIOParam(tp);
-	return OidInputFunctionCall(typinput, string,
-								typioparam, atttypmod);
+	result = OidInputFunctionCall(typinput, string,
+								  typioparam, atttypmod);
+
+#ifdef RANDOMIZE_ALLOCATED_MEMORY
+	/*
+	 * For pass-by-reference data types, repeat the conversion to see if the
+	 * input function leaves any uninitialized bytes in the result.  We can
+	 * only detect that reliably if RANDOMIZE_ALLOCATED_MEMORY is enabled,
+	 * so we don't bother testing otherwise.  The reason we don't want any
+	 * instability in the input function is that comparison of Const nodes
+	 * relies on bytewise comparison of the datums, so if the input function
+	 * leaves garbage then subexpressions that should be identical may not get
+	 * recognized as such.  See pgsql-hackers discussion of 2008-04-04.
+	 */
+	if (string && !typform->typbyval)
+	{
+		Datum		result2;
+
+		result2 = OidInputFunctionCall(typinput, string,
+									   typioparam, atttypmod);
+		if (!datumIsEqual(result, result2, typform->typbyval, typform->typlen))
+			elog(WARNING, "type %s has unstable input conversion for \"%s\"",
+				 NameStr(typform->typname), string);
+	}
+#endif
+
+	return result;
 }
 
 /* given a typeid, return the type's typrelid (associated relation, if any) */

src/backend/utils/mmgr/aset.c

@@ -11,7 +11,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/mmgr/aset.c,v 1.76 2008/01/01 19:45:55 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/mmgr/aset.c,v 1.77 2008/04/11 22:54:23 tgl Exp $
  *
  * NOTE:
  *	This is a new (Feb. 05, 1999) implementation of the allocation set
@@ -282,6 +282,32 @@ AllocSetFreeIndex(Size size)
 	return idx;
 }
 
+#ifdef RANDOMIZE_ALLOCATED_MEMORY
+
+/*
+ * Fill a just-allocated piece of memory with "random" data.  It's not really
+ * very random, just a repeating sequence with a length that's prime.  What
+ * we mainly want out of it is to have a good probability that two palloc's
+ * of the same number of bytes start out containing different data.
+ */
+static void
+randomize_mem(char *ptr, size_t size)
+{
+	static int	save_ctr = 1;
+	int			ctr;
+
+	ctr = save_ctr;
+	while (size-- > 0)
+	{
+		*ptr++ = ctr;
+		if (++ctr > 251)
+			ctr = 1;
+	}
+	save_ctr = ctr;
+}
+
+#endif /* RANDOMIZE_ALLOCATED_MEMORY */
+
 
 /*
  * Public routines
@@ -552,6 +578,10 @@ AllocSetAlloc(MemoryContext context, Size size)
 		if (size < chunk_size)
 			((char *) AllocChunkGetPointer(chunk))[size] = 0x7E;
 #endif
+#ifdef RANDOMIZE_ALLOCATED_MEMORY
+		/* fill the allocated space with junk */
+		randomize_mem((char *) AllocChunkGetPointer(chunk), size);
+#endif
 
 		/*
 		 * Stick the new block underneath the active allocation block, so that
@@ -596,6 +626,10 @@ AllocSetAlloc(MemoryContext context, Size size)
 		if (size < chunk->size)
 			((char *) AllocChunkGetPointer(chunk))[size] = 0x7E;
 #endif
+#ifdef RANDOMIZE_ALLOCATED_MEMORY
+		/* fill the allocated space with junk */
+		randomize_mem((char *) AllocChunkGetPointer(chunk), size);
+#endif
 
 		/* isReset must be false already */
 		Assert(!set->isReset);
@@ -752,6 +786,10 @@ AllocSetAlloc(MemoryContext context, Size size)
 	if (size < chunk->size)
 		((char *) AllocChunkGetPointer(chunk))[size] = 0x7E;
 #endif
+#ifdef RANDOMIZE_ALLOCATED_MEMORY
+	/* fill the allocated space with junk */
+	randomize_mem((char *) AllocChunkGetPointer(chunk), size);
+#endif
 
 	set->isReset = false;
 
@@ -864,6 +902,13 @@ AllocSetRealloc(MemoryContext context, void *pointer, Size size)
 	if (oldsize >= size)
 	{
 #ifdef MEMORY_CONTEXT_CHECKING
+#ifdef RANDOMIZE_ALLOCATED_MEMORY
+		/* We can only fill the extra space if we know the prior request */
+		if (size > chunk->requested_size)
+			randomize_mem((char *) AllocChunkGetPointer(chunk) + chunk->requested_size,
+						  size - chunk->requested_size);
+#endif
+
 		chunk->requested_size = size;
 		/* set mark to catch clobber of "unused" space */
 		if (size < oldsize)
@@ -921,6 +966,12 @@ AllocSetRealloc(MemoryContext context, void *pointer, Size size)
 		chunk->size = chksize;
 
 #ifdef MEMORY_CONTEXT_CHECKING
+#ifdef RANDOMIZE_ALLOCATED_MEMORY
+		/* We can only fill the extra space if we know the prior request */
+		randomize_mem((char *) AllocChunkGetPointer(chunk) + chunk->requested_size,
+					  size - chunk->requested_size);
+#endif
+
 		chunk->requested_size = size;
 		/* set mark to catch clobber of "unused" space */
 		if (size < chunk->size)

src/include/pg_config_manual.h

@@ -6,7 +6,7 @@
  * for developers.	If you edit any of these, be sure to do a *full*
  * rebuild (and an initdb if noted).
  *
- * $PostgreSQL: pgsql/src/include/pg_config_manual.h,v 1.30 2008/03/27 03:57:34 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/pg_config_manual.h,v 1.31 2008/04/11 22:54:23 tgl Exp $
  *------------------------------------------------------------------------
  */
 
@@ -214,11 +214,19 @@
  *------------------------------------------------------------------------
  */
 
+/*
+ * Define this to cause palloc()'d memory to be filled with random data, to
+ * facilitate catching code that depends on the contents of uninitialized
+ * memory.  Right now, this gets defined automatically if --enable-cassert.
+ */
+#ifdef USE_ASSERT_CHECKING
+#define RANDOMIZE_ALLOCATED_MEMORY
+#endif
+
 /*
  * Define this to cause pfree()'d memory to be cleared immediately, to
- * facilitate catching bugs that refer to already-freed values.  XXX
- * Right now, this gets defined automatically if --enable-cassert.	In
- * the long term it probably doesn't need to be on by default.
+ * facilitate catching bugs that refer to already-freed values.
+ * Right now, this gets defined automatically if --enable-cassert.
  */
 #ifdef USE_ASSERT_CHECKING
 #define CLOBBER_FREED_MEMORY
@@ -227,8 +235,7 @@
 /*
  * Define this to check memory allocation errors (scribbling on more
  * bytes than were allocated).	Right now, this gets defined
- * automatically if --enable-cassert.  In the long term it probably
- * doesn't need to be on by default.
+ * automatically if --enable-cassert.
  */
 #ifdef USE_ASSERT_CHECKING
 #define MEMORY_CONTEXT_CHECKING