[PATCH akpm] compiler-intel: fix wrong compiler barrier() macro

[Daniel Borkmann]

Cleanup commit 73679e508201 ("compiler-intel.h: Remove duplicate
definition") removed the double definition of __memory_barrier()
intrinsics.

However, in doing so, it also removed the preceding #undef barrier
by accident, meaning, the actual barrier() macro from compiler-gcc.h
with inline asm is still in place as __GNUC__ is provided.

Subsequently, barrier() can never be defined as __memory_barrier()
from compiler.h since it already has a definition in place and if
we trust the comment in compiler-intel.h, ecc doesn't support gcc
specific asm statements.

I don't have an ecc at hand (unsure if that's still used in the
field?) and only found this by accident during code review, a revert
of that cleanup would be simplest option.

Fixes: 73679e508201 ("compiler-intel.h: Remove duplicate definition")
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Reviewed-by: Pranith Kumar <bobby.prani@xxxxxxxxx>
Cc: Pranith Kumar <bobby.prani@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: mancha security <mancha1@xxxxxxxx>
---
 Only resending fix for Andrew's tree, rebased.

 include/linux/compiler-intel.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/compiler-intel.h b/include/linux/compiler-intel.h
index 0c9a2f2..d4c7113 100644
--- a/include/linux/compiler-intel.h
+++ b/include/linux/compiler-intel.h
@@ -13,10 +13,12 @@
 /* Intel ECC compiler doesn't support gcc specific asm stmts.
  * It uses intrinsics to do the equivalent things.
  */
+#undef barrier
 #undef barrier_data
 #undef RELOC_HIDE
 #undef OPTIMIZER_HIDE_VAR
 
+#define barrier() __memory_barrier()
 #define barrier_data(ptr) barrier()
 
 #define RELOC_HIDE(ptr, off)					\
-- 
1.9.3

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