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

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Commit-ID:  121843eb02a6e2fa30aefab64bfe183c97230c75
Gitweb:     http://git.kernel.org/tip/121843eb02a6e2fa30aefab64bfe183c97230c75
Author:     Matthias Kaehlcke <mka@chromium.org>
AuthorDate: Mon, 1 May 2017 15:47:41 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 5 May 2017 08:31:05 +0200

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

diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index 7acb51c..7a9df3b 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -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)
diff --git a/arch/x86/lib/kaslr.c b/arch/x86/lib/kaslr.c
index 5761a4f..ab2d1d7 100644
--- a/arch/x86/lib/kaslr.c
+++ b/arch/x86/lib/kaslr.c
@@ -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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[PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication Matthias Kaehlcke <mka@chromium.org> - 2017-05-02 00:50 +0200
  Re: [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication Kees Cook <keescook@chromium.org> - 2017-05-02 04:10 +0200
  [tip:x86/urgent] x86/mm/kaslr: Use the _ASM_MUL macro for  multiplication to work around Clang incompatibility tip-bot for Matthias Kaehlcke <tipbot@zytor.com> - 2017-05-05 10:30 +0200
    Re: [tip:x86/urgent] x86/mm/kaslr: Use the _ASM_MUL macro for  multiplication to work around Clang incompatibility Peter Zijlstra <peterz@infradead.org> - 2017-05-05 12:30 +0200
      Re: [tip:x86/urgent] x86/mm/kaslr: Use the _ASM_MUL macro for  multiplication to work around Clang incompatibility Ingo Molnar <mingo@kernel.org> - 2017-05-05 20:00 +0200
        Re: [tip:x86/urgent] x86/mm/kaslr: Use the _ASM_MUL macro for  multiplication to work around Clang incompatibility Peter Zijlstra <peterz@infradead.org> - 2017-05-05 20:30 +0200
        Re: [tip:x86/urgent] x86/mm/kaslr: Use the _ASM_MUL macro for  multiplication to work around Clang incompatibility Matthias Kaehlcke <mka@chromium.org> - 2017-05-05 20:50 +0200
          Re: [tip:x86/urgent] x86/mm/kaslr: Use the _ASM_MUL macro for  multiplication to work around Clang incompatibility Linus Torvalds <torvalds@linux-foundation.org> - 2017-05-05 21:40 +0200
            Re: [tip:x86/urgent] x86/mm/kaslr: Use the _ASM_MUL macro for  multiplication to work around Clang incompatibility Michael Davidson <md@google.com> - 2017-05-05 22:40 +0200
              Re: [tip:x86/urgent] x86/mm/kaslr: Use the _ASM_MUL macro for  multiplication to work around Clang incompatibility Peter Zijlstra <peterz@infradead.org> - 2017-05-06 10:20 +0200
                Re: [tip:x86/urgent] x86/mm/kaslr: Use the _ASM_MUL macro for multiplication to work around Clang incompatibility hpa@zytor.com - 2017-05-08 00:10 +0200
            Re: [tip:x86/urgent] x86/mm/kaslr: Use the _ASM_MUL macro for  multiplication to work around Clang incompatibility Matthias Kaehlcke <mka@chromium.org> - 2017-05-05 23:00 +0200
              Re: [tip:x86/urgent] x86/mm/kaslr: Use the _ASM_MUL macro for  multiplication to work around Clang incompatibility Ingo Molnar <mingo@kernel.org> - 2017-05-06 12:00 +0200
          Re: [tip:x86/urgent] x86/mm/kaslr: Use the _ASM_MUL macro for multiplication to work around Clang incompatibility hpa@zytor.com - 2017-05-05 22:00 +0200
            Re: [tip:x86/urgent] x86/mm/kaslr: Use the _ASM_MUL macro for  multiplication to work around Clang incompatibility Matthias Kaehlcke <mka@chromium.org> - 2017-05-05 23:30 +0200

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