Add comments that Solaris Sun compiler only supports sparc9 ASM,

src/backend/port/tas/solaris_sparc.s

@@ -16,6 +16,23 @@
 	.global pg_atomic_cas
 pg_atomic_cas:
 	
+	! "cas" only works on sparcv9 chips, and requies a compiler
+	! that is targeting sparcv9.  It will fail on a compiler
+	! targeting sparcv8, and of course will not be understood
+	! by a sparcv8 CPU.  If this fails on existing Solaris
+	! systems, we need to use a !defined(__sparcv9) test
+	! to fall back to the old "ldstub" call for sparcv8 compiles.
+	! gcc continues to use "ldstub" because there is no indication
+	! which sparc version it is targeting.
+	!
+	! There actually is a trick for embedding "cas" for a compiler
+	! that is targeting sparcv8:
+	!
+	!   http://cvs.opensolaris.org/source/xref/on/usr/src/lib/libc/sparc/threads/sparc.il
+	!
+	! This might work for sparc8:
+	! ldstub [%o0],%o1	! moves only a byte
+
 	cas     [%o0],%o2,%o1
 	mov     %o1,%o0
 	retl

src/include/storage/s_lock.h

@@ -66,7 +66,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	  $PostgreSQL: pgsql/src/include/storage/s_lock.h,v 1.152 2006/04/29 11:55:19 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/include/storage/s_lock.h,v 1.153 2006/05/17 23:57:03 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -311,6 +311,10 @@ tas(volatile slock_t *lock)
 {
 	register slock_t _res;
 
+	/*
+	 *	See comment in /pg/backend/port/tas/solaris_sparc.s for why this
+	 *	uses "ldstub", and that file uses "cas".
+	 */
 	__asm__ __volatile__(
 		"	ldstub	[%2], %0	\n"
 :		"=r"(_res), "+m"(*lock)