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   1 From foo@baz Mon Apr  9 17:09:24 CEST 2018
   2 From: Matthias Kaehlcke <mka@chromium.org>
   3 Date: Mon, 1 May 2017 15:47:41 -0700
   4 Subject: x86/mm/kaslr: Use the _ASM_MUL macro for multiplication to work around Clang incompatibility
   5
   6 From: Matthias Kaehlcke <mka@chromium.org>
   7
   8
   9 [ Upstream commit 121843eb02a6e2fa30aefab64bfe183c97230c75 ]
  10
  11 The constraint "rm" allows the compiler to put mix_const into memory.
  12 When the input operand is a memory location then MUL needs an operand
  13 size suffix, since Clang can't infer the multiplication width from the
  14 operand.
  15
  16 Add and use the _ASM_MUL macro which determines the operand size and
  17 resolves to the NUL instruction with the corresponding suffix.
  18
  19 This fixes the following error when building with clang:
  20
  21   CC      arch/x86/lib/kaslr.o
  22   /tmp/kaslr-dfe1ad.s: Assembler messages:
  23   /tmp/kaslr-dfe1ad.s:182: Error: no instruction mnemonic suffix given and no register operands; can't size instruction
  24
  25 Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
  26 Cc: Grant Grundler <grundler@chromium.org>
  27 Cc: Greg Hackmann <ghackmann@google.com>
  28 Cc: Kees Cook <keescook@chromium.org>
  29 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  30 Cc: Michael Davidson <md@google.com>
  31 Cc: Peter Zijlstra <peterz@infradead.org>
  32 Cc: Thomas Gleixner <tglx@linutronix.de>
  33 Link: http://lkml.kernel.org/r/20170501224741.133938-1-mka@chromium.org
  34 Signed-off-by: Ingo Molnar <mingo@kernel.org>
  35 Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
  36 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  37 ---
  38  arch/x86/include/asm/asm.h |    1 +
  39  arch/x86/lib/kaslr.c       |    3 ++-
  40  2 files changed, 3 insertions(+), 1 deletion(-)
  41
  42 --- a/arch/x86/include/asm/asm.h
  43 +++ b/arch/x86/include/asm/asm.h
  44 @@ -34,6 +34,7 @@
  45  #define _ASM_ADD       __ASM_SIZE(add)
  46  #define _ASM_SUB       __ASM_SIZE(sub)
  47  #define _ASM_XADD      __ASM_SIZE(xadd)
  48 +#define _ASM_MUL       __ASM_SIZE(mul)
  49
  50  #define _ASM_AX                __ASM_REG(ax)
  51  #define _ASM_BX                __ASM_REG(bx)
  52 --- a/arch/x86/lib/kaslr.c
  53 +++ b/arch/x86/lib/kaslr.c
  54 @@ -5,6 +5,7 @@
  55   * kernel starts. This file is included in the compressed kernel and
  56   * normally linked in the regular.
  57   */
  58 +#include <asm/asm.h>
  59  #include <asm/kaslr.h>
  60  #include <asm/msr.h>
  61  #include <asm/archrandom.h>
  62 @@ -79,7 +80,7 @@ unsigned long kaslr_get_random_long(cons
  63         }
  64
  65         /* Circular multiply for better bit diffusion */
  66 -       asm("mul %3"
  67 +       asm(_ASM_MUL "%3"
  68             : "=a" (random), "=d" (raw)
  69             : "a" (random), "rm" (mix_const));
  70         random += raw;