From be23ddb4ee437d9c8a902dcc19cf0d1633c23de2 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh@NetBSD.org>
Date: Fri, 11 Feb 2022 21:29:26 +0000
Subject: [PATCH 02/49] sparc64: Fix membar_sync by issuing membar #StoreLoad.
In TSO this is the only memory barrier ever needed, and somehow we
got this wrong and instead issued an unnecessary membar #LoadLoad --
not needed even in PSO let alone in TSO.
XXX Apparently we may run userland programs with PSO or RMO, in which
case all of these membars need fixing:
PSO RMO
membar_consumer nop membar #LoadLoad
membar_producer membar #StoreStore membar #StoreStore
membar_enter nop membar #LoadLoad|LoadStore
membar_exit membar #StoreStore membar #LoadStore|StoreStore
membar_sync membar #StoreLoad|StoreStore
membar #...everything...
But at least this fixes the TSO case in which we run the kernel.
Also I'm not sure there's any non-TSO hardware out there in practice.
---
.../lib/libc/arch/sparc64/atomic/membar_ops.S | 27 ++++++++++++-------
1 file changed, 18 insertions(+), 9 deletions(-)
diff --git a/common/lib/libc/arch/sparc64/atomic/membar_ops.S b/common/lib/libc/arch/sparc64/atomic/membar_ops.S
index a3f5cb59f265..034d93b30a0d 100644
--- a/common/lib/libc/arch/sparc64/atomic/membar_ops.S
+++ b/common/lib/libc/arch/sparc64/atomic/membar_ops.S
@@ -15,7 +15,7 @@
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
- *
+ *
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
@@ -33,22 +33,31 @@
.text
-/* These assume Total Store Order (TSO) */
+/*
+ * These assume Total Store Order (TSO), which may reorder
+ * store-before-load but nothing else. Hence, only membar_sync must
+ * issue anything -- namely, membar #StoreLoad.
+ *
+ * If we ran with Partial Store Order (PSO), we would also need to
+ * issue membar #StoreStore for membar_exit (load/store-before-store)
+ * and membar_producer (store-before-store).
+ */
-ENTRY(_membar_producer)
+ENTRY(_membar_consumer)
retl
nop
+END(_membar_consumer)
-ENTRY(_membar_consumer)
- membar #LoadLoad
+ENTRY(_membar_sync)
retl
- nop
+ membar #StoreLoad
+END(_membar_sync)
-ATOMIC_OP_ALIAS(membar_producer,_membar_producer)
+ATOMIC_OP_ALIAS(membar_producer,_membar_consumer)
+STRONG_ALIAS(_membar_producer,_membar_consumer)
ATOMIC_OP_ALIAS(membar_consumer,_membar_consumer)
ATOMIC_OP_ALIAS(membar_enter,_membar_consumer)
STRONG_ALIAS(_membar_enter,_membar_consumer)
ATOMIC_OP_ALIAS(membar_exit,_membar_consumer)
STRONG_ALIAS(_membar_exit,_membar_consumer)
-ATOMIC_OP_ALIAS(membar_sync,_membar_consumer)
-STRONG_ALIAS(_membar_sync,_membar_consumer)
+ATOMIC_OP_ALIAS(membar_sync,_membar_sync)
--
2.33.0