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Subject[PATCH RFC 1/4] include/linux/compiler*.h: fix OPTIMIZER_HIDE_VAR
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@codeaurora.org>
Cc: Joe Perches <joe@perches.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
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 3e7dafb3ea80..7ddaeb5182e3 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 2010493e1040..72054d9f0eaa 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 517bd14e1222..b17f3cd18334 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 06396c1cf127..1ad367b4cd8d 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -152,7 +152,9 @@ 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. */
--
MST
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