Cooperate with the Valgrind instrumentation framework.

Valgrind "client requests" in aset.c and mcxt.c teach Valgrind and its
Memcheck tool about the PostgreSQL allocator.  This makes Valgrind
roughly as sensitive to memory errors involving palloc chunks as it is
to memory errors involving malloc chunks.  Further client requests in
PageAddItem() and printtup() verify that all bits being added to a
buffer page or furnished to an output function are predictably-defined.
Those tests catch failures of C-language functions to fully initialize
the bits of a Datum, which in turn stymie optimizations that rely on
_equalConst().  Define the USE_VALGRIND symbol in pg_config_manual.h to
enable these additions.  An included "suppression file" silences nominal
errors we don't plan to fix.

Reviewed in earlier versions by Peter Geoghegan and Korry Douglas.

src/tools/valgrind.supp

@@ -0,0 +1,94 @@
+# This is a suppression file for use with Valgrind tools.  File format
+# documentation:
+#	http://valgrind.org/docs/manual/mc-manual.html#mc-manual.suppfiles
+
+# The libc symbol that implements a particular standard interface is
+# implementation-dependent.  For example, strncpy() shows up as "__GI_strncpy"
+# on some platforms.  Use wildcards to avoid mentioning such specific names.
+
+
+# We have occasion to write raw binary structures to disk or to the network.
+# These may contain uninitialized padding bytes.  Since recipients also ignore
+# those bytes as padding, this is harmless.
+
+{
+	padding_pgstat_send
+	Memcheck:Param
+	socketcall.send(msg)
+
+	fun:*send*
+	fun:pgstat_send
+}
+
+{
+	padding_pgstat_sendto
+	Memcheck:Param
+	socketcall.sendto(msg)
+
+	fun:*send*
+	fun:pgstat_send
+}
+
+{
+	padding_pgstat_write
+	Memcheck:Param
+	write(buf)
+
+	...
+	fun:pgstat_write_statsfiles
+}
+
+{
+	padding_XLogRecData_CRC
+	Memcheck:Value8
+
+	fun:XLogInsert
+}
+
+{
+	padding_XLogRecData_write
+	Memcheck:Param
+	write(buf)
+
+    ...
+	fun:XLogWrite
+}
+
+{
+	padding_relcache
+	Memcheck:Param
+	write(buf)
+
+	...
+	fun:write_relcache_init_file
+}
+
+
+# resolve_polymorphic_tupdesc(), a subroutine of internal_get_result_type(),
+# can instigate a memcpy() call where the two pointer arguments are exactly
+# equal.  The behavior thereof is formally undefined, but implementations
+# where it's anything other than a no-op are thought unlikely.
+{
+	noopmemcpy_internal_get_result_type
+	Memcheck:Overlap
+
+	fun:*strncpy*
+	fun:namestrcpy
+	fun:TupleDescInitEntry
+	...
+	fun:internal_get_result_type
+}
+
+
+# gcc on ppc64 can generate a four-byte read to fetch the final "char" fields
+# of a FormData_pg_cast.  This is valid compiler behavior, because a proper
+# FormData_pg_cast has trailing padding.  Tuples we treat as structures omit
+# that padding, so Valgrind reports an invalid read.  Practical trouble would
+# entail the missing pad bytes falling in a different memory page.  So long as
+# the structure is aligned, that will not happen.
+{
+	overread_tuplestruct_pg_cast
+	Memcheck:Addr4
+
+	fun:IsBinaryCoercible
+}