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   1 From foo@baz Wed Nov 21 18:50:39 CET 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 commit 121843eb02a6e2fa30aefab64bfe183c97230c75 upstream.
   9
  10 The constraint "rm" allows the compiler to put mix_const into memory.
  11 When the input operand is a memory location then MUL needs an operand
  12 size suffix, since Clang can't infer the multiplication width from the
  13 operand.
  14
  15 Add and use the _ASM_MUL macro which determines the operand size and
  16 resolves to the NUL instruction with the corresponding suffix.
  17
  18 This fixes the following error when building with clang:
  19
  20   CC      arch/x86/lib/kaslr.o
  21   /tmp/kaslr-dfe1ad.s: Assembler messages:
  22   /tmp/kaslr-dfe1ad.s:182: Error: no instruction mnemonic suffix given and no register operands; can't size instruction
  23
  24 Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
  25 Cc: Grant Grundler <grundler@chromium.org>
  26 Cc: Greg Hackmann <ghackmann@google.com>
  27 Cc: Kees Cook <keescook@chromium.org>
  28 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  29 Cc: Michael Davidson <md@google.com>
  30 Cc: Peter Zijlstra <peterz@infradead.org>
  31 Cc: Thomas Gleixner <tglx@linutronix.de>
  32 Link: http://lkml.kernel.org/r/20170501224741.133938-1-mka@chromium.org
  33 Signed-off-by: Ingo Molnar <mingo@kernel.org>
  34 [nc: Apply to aslr.c in get_random_long as the kaslr shift didn't happen
  35      until 4.8 in commit d899a7d146a2]
  36 Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
  37 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  38 ---
  39  arch/x86/boot/compressed/aslr.c |    3 ++-
  40  arch/x86/include/asm/asm.h      |    1 +
  41  2 files changed, 3 insertions(+), 1 deletion(-)
  42
  43 --- a/arch/x86/boot/compressed/aslr.c
  44 +++ b/arch/x86/boot/compressed/aslr.c
  45 @@ -1,5 +1,6 @@
  46  #include "misc.h"
  47
  48 +#include <asm/asm.h>
  49  #include <asm/msr.h>
  50  #include <asm/archrandom.h>
  51  #include <asm/e820.h>
  52 @@ -94,7 +95,7 @@ static unsigned long get_random_long(voi
  53         }
  54
  55         /* Circular multiply for better bit diffusion */
  56 -       asm("mul %3"
  57 +       asm(_ASM_MUL "%3"
  58             : "=a" (random), "=d" (raw)
  59             : "a" (random), "rm" (mix_const));
  60         random += raw;
  61 --- a/arch/x86/include/asm/asm.h
  62 +++ b/arch/x86/include/asm/asm.h
  63 @@ -34,6 +34,7 @@
  64  #define _ASM_ADD       __ASM_SIZE(add)
  65  #define _ASM_SUB       __ASM_SIZE(sub)
  66  #define _ASM_XADD      __ASM_SIZE(xadd)
  67 +#define _ASM_MUL       __ASM_SIZE(mul)
  68
  69  #define _ASM_AX                __ASM_REG(ax)
  70  #define _ASM_BX                __ASM_REG(bx)