Merge branch 'linus' into x86/cleanups, before applying dependent patch

1 files changed, 15 insertions, 1 deletions

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index cdf13ca7cac3..371e560d13cf 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -9,10 +9,24 @@
 		   + __GNUC_MINOR__ * 100 \
 		   + __GNUC_PATCHLEVEL__)
 
-
 /* Optimization barrier */
+
 /* The "volatile" is due to gcc bugs */
 #define barrier() __asm__ __volatile__("": : :"memory")
+/*
+ * This version is i.e. to prevent dead stores elimination on @ptr
+ * where gcc and llvm may behave differently when otherwise using
+ * normal barrier(): while gcc behavior gets along with a normal
+ * barrier(), llvm needs an explicit input variable to be assumed
+ * clobbered. The issue is as follows: while the inline asm might
+ * access any memory it wants, the compiler could have fit all of
+ * @ptr into memory registers instead, and since @ptr never escaped
+ * from that, it proofed that the inline asm wasn't touching any of
+ * it. This version works well with both compilers, i.e. we're telling
+ * the compiler that the inline asm absolutely may see the contents
+ * of @ptr. See also: https://llvm.org/bugs/show_bug.cgi?id=15495
+ */
+#define barrier_data(ptr) __asm__ __volatile__("": :"r"(ptr) :"memory")
 
 /*
  * This macro obfuscates arithmetic on a variable address so that gcc