On Mon, Jul 06, 2020 at 05:08:20PM +0100, Dave Martin wrote:
On Tue, Jun 30, 2020 at 06:37:34PM +0100, Will Deacon wrote:
quoted
diff --git a/arch/arm64/include/asm/rwonce.h b/arch/arm64/include/asm/rwonce.h
new file mode 100644
index 000000000000..515e360b01a1
--- /dev/null
+++ b/arch/arm64/include/asm/rwonce.h
@@ -0,0 +1,63 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020 Google LLC.
+ */
+#ifndef __ASM_RWONCE_H
+#define __ASM_RWONCE_H
+
+#ifdef CONFIG_CLANG_LTO
+
+#include <linux/compiler_types.h>
+#include <asm/alternative-macros.h>
+
+#ifndef BUILD_VDSO
+
+#ifdef CONFIG_AS_HAS_LDAPR
+#define __LOAD_RCPC(sfx, regs...) \
+ ALTERNATIVE( \
+ "ldar" #sfx "\t" #regs, \
^ Should this be here? It seems that READ_ONCE() will actually read
twice... even if that doesn't actually conflict with the required
semantics of READ_ONCE(), it looks odd.
It's patched at runtime, so it's either LDAR or LDAPR.
Making a direct link between LTO and the memory model also seems highly
spurious (as discussed in the other subthread) so can we have a comment
explaining the reasoning?
Sure, although like I say, this is more about helping to progress that
conversation.
Will