Patch "x86/mm/kaslr: Use the _ASM_MUL macro for multiplication to work around Clang incompatibility" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

x86/mm/kaslr: Use the _ASM_MUL macro for multiplication to work around Clang incompatibility

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-mm-kaslr-use-the-_asm_mul-macro-for-multiplication-to-work-around-clang-incompatibility.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Matthias Kaehlcke <[email protected]>
Date: Mon, 1 May 2017 15:47:41 -0700
Subject: x86/mm/kaslr: Use the _ASM_MUL macro for multiplication to work around Clang incompatibility

From: Matthias Kaehlcke <[email protected]>

[ Upstream commit 121843eb02a6e2fa30aefab64bfe183c97230c75 ]

The constraint "rm" allows the compiler to put mix_const into memory. When the input operand is a memory location then MUL needs an operand size suffix, since Clang can't infer the multiplication width from the operand.

Add and use the _ASM_MUL macro which determines the operand size and resolves to the NUL instruction with the corresponding suffix.

This fixes the following error when building with clang:

CC arch/x86/lib/kaslr.o
/tmp/kaslr-dfe1ad.s: Assembler messages:
/tmp/kaslr-dfe1ad.s:182: Error: no instruction mnemonic suffix given and no register operands; can't size instruction

---
 arch/x86/include/asm/asm.h |    1 +
 arch/x86/lib/kaslr.c       |    3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

@@ -34,6 +34,7 @@
 #define _ASM_ADD	__ASM_SIZE(add)
 #define _ASM_SUB	__ASM_SIZE(sub)
 #define _ASM_XADD	__ASM_SIZE(xadd)
+#define _ASM_MUL	__ASM_SIZE(mul)
 
 #define _ASM_AX		__ASM_REG(ax)
 #define _ASM_BX		__ASM_REG(bx)

@@ -5,6 +5,7 @@
  * kernel starts. This file is included in the compressed kernel and
  * normally linked in the regular.
  */
+#include <asm/asm.h>
 #include <asm/kaslr.h>
 #include <asm/msr.h>
 #include <asm/archrandom.h>

@@ -79,7 +80,7 @@ unsigned long kaslr_get_random_long(cons
 	}
 
 	/* Circular multiply for better bit diffusion */
-	asm("mul %3"
+	asm(_ASM_MUL "%3"
 	    : "=a" (random), "=d" (raw)
 	    : "a" (random), "rm" (mix_const));
 	random += raw;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/x86-mm-kaslr-use-the-_asm_mul-macro-for-multiplication-to-work-around-clang-incompatibility.patch