linux-kernel - [PATCH 4.19 050/152] include/linux/compiler*.h: fix OPTIMIZER_HIDE

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Message-Id: <20190225195047.092405649@linuxfoundation.org>
Date:   Mon, 25 Feb 2019 22:10:42 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eli Friedman <efriedma@...eaurora.org>,
        Joe Perches <joe@...ches.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 050/152] include/linux/compiler*.h: fix OPTIMIZER_HIDE_VAR

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 3e2ffd655cc6a694608d997738989ff5572a8266 ]

Since commit 815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h
mutually exclusive") clang no longer reuses the OPTIMIZER_HIDE_VAR macro
from compiler-gcc - instead it gets the version in
include/linux/compiler.h.  Unfortunately that version doesn't actually
prevent compiler from optimizing out the variable.

Fix up by moving the macro out from compiler-gcc.h to compiler.h.
Compilers without incline asm support will keep working
since it's protected by an ifdef.

Also fix up comments to match reality since we are no longer overriding
any macros.

Build-tested with gcc and clang.

Fixes: 815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h mutually exclusive")
Cc: Eli Friedman <efriedma@...eaurora.org>
Cc: Joe Perches <joe@...ches.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 include/linux/compiler-clang.h | 5 ++---
 include/linux/compiler-gcc.h   | 4 ----
 include/linux/compiler-intel.h | 4 +---
 include/linux/compiler.h       | 4 +++-
 4 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index b1ce500fe8b3d..d756f2318efe0 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -3,9 +3,8 @@
 #error "Please don't include <linux/compiler-clang.h> directly, include <linux/compiler.h> instead."
 #endif
 
-/* Some compiler specific definitions are overwritten here
- * for Clang compiler
- */
+/* Compiler specific definitions for Clang compiler */
+
 #define uninitialized_var(x) x = *(&(x))
 
 /* same as gcc, this was present in clang-2.6 so we can assume it works
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 0242f6eec4eaf..a8ff0ca0c3213 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -58,10 +58,6 @@
 	(typeof(ptr)) (__ptr + (off));					\
 })
 
-/* Make the optimizer believe the variable can be manipulated arbitrarily. */
-#define OPTIMIZER_HIDE_VAR(var)						\
-	__asm__ ("" : "=r" (var) : "0" (var))
-
 /*
  * A trick to suppress uninitialized variable warning without generating any
  * code
diff --git a/include/linux/compiler-intel.h b/include/linux/compiler-intel.h
index 4c7f9befa9f6c..f1fc60f103176 100644
--- a/include/linux/compiler-intel.h
+++ b/include/linux/compiler-intel.h
@@ -5,9 +5,7 @@
 
 #ifdef __ECC
 
-/* Some compiler specific definitions are overwritten here
- * for Intel ECC compiler
- */
+/* Compiler specific definitions for Intel ECC compiler */
 
 #include <asm/intrinsics.h>
 
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 681d866efb1eb..269d376f5a119 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -158,7 +158,9 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 #endif
 
 #ifndef OPTIMIZER_HIDE_VAR
-#define OPTIMIZER_HIDE_VAR(var) barrier()
+/* Make the optimizer believe the variable can be manipulated arbitrarily. */
+#define OPTIMIZER_HIDE_VAR(var)						\
+	__asm__ ("" : "=r" (var) : "0" (var))
 #endif
 
 /* Not-quite-unique ID. */
-- 
2.19.1