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Commit cafc5bc7 authored by Matthias Kaehlcke's avatar Matthias Kaehlcke Committed by Greg Hackmann
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BACKPORT: x86/mm/kaslr: Use the _ASM_MUL macro for multiplication to work... 


BACKPORT: 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

Upstream commit: 121843eb02a6

Change-Id: I53f51839705dabeb6c950d1def3a45881294129c
Signed-off-by: default avatarMatthias 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: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarGreg Hackmann <ghackmann@google.com>
parent 2a3a3862

arch/x86/boot/compressed/aslr.c

+1 −1
Original line number Diff line number Diff line
@@ -94,7 +94,7 @@ static unsigned long get_random_long(void) 
	}



	/* Circular multiply for better bit diffusion */

	asm("mul %3"

	asm(_ASM_MUL "%3"

	    : "=a" (random), "=d" (raw)

	    : "a" (random), "rm" (mix_const));

	random += raw;

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)