Commit 121843eb authored May 01, 2017 by Matthias Kaehlcke Committed by Ingo Molnar May 05, 2017

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



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

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Cc: Grant Grundler <grundler@chromium.org>
Cc: Greg Hackmann <ghackmann@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Davidson <md@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170501224741.133938-1-mka@chromium.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent fc5f9d5f

arch/x86/include/asm/asm.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -32,6 +32,7 @@
		#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)

arch/x86/lib/kaslr.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -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(const char *purpose)
		}

		/* Circular multiply for better bit diffusion */
		asm("mul %3"
		asm(_ASM_MUL "%3"
		: "=a" (random), "=d" (raw)
		: "a" (random), "rm" (mix_const));
		random += raw;

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