kvm-unit-tests: fix build on x86-64 with specific gcc versions

kvm-unit-tests uses the following code on x86/x86-64:

static inline u64 scale_delta(u64 delta, u64 mul_frac)
{
        u64 product, unused;

        __asm__ (
                "mul %3"
                : "=d" (product), "=a" (unused) : "1" (delta), "rm" ((u64)mul_frac) );

        return product;
}

The "mul" instruction does not have a suffix that indicates the width of
the data being multiplied. When the data is passed in a register, there
is no need to specify the width, but with some gcc versions, the data is
passed as a memory reference, and therefore the assembler does not know
the width of the data to be multiplied. It causes the following build
failure:

x86/hyperv_clock.c: Assembler messages:
x86/hyperv_clock.c:21: Error: no instruction mnemonic suffix given and no register operands; can't size instruction

Since the data being multiplied is 64 bit, we explicitly specify the
instruction as being "mulq".

Fixes:

  http://autobuild.buildroot.net/results/a4a65d01f049db83a93de92660f228dd18532625/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/kvm-unit-tests/0001-x86-hyperv_clock-be-explicit-about-mul-instruction-d.patch

@@ -0,0 +1,35 @@
+From 022ae220d6e7b5bd064bc8698c271dca4dac7d8c Mon Sep 17 00:00:00 2001
+From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+Date: Mon, 8 May 2017 22:27:25 +0200
+Subject: [PATCH] x86/hyperv_clock: be explicit about mul instruction data size
+
+With gcc 4.7.2, the build fails with:
+
+x86/hyperv_clock.c: Assembler messages:
+x86/hyperv_clock.c:21: Error: no instruction mnemonic suffix given and no register operands; can't size instruction
+
+In order to avoid this, make the mul instruction data size explicit by
+adding the appropriate suffix. It operates on 64-bit data, so use
+"mulq".
+
+Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+---
+ x86/hyperv_clock.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/x86/hyperv_clock.c b/x86/hyperv_clock.c
+index 8b1deba..6c4dd56 100644
+--- a/x86/hyperv_clock.c
++++ b/x86/hyperv_clock.c
+@@ -19,7 +19,7 @@ static inline u64 scale_delta(u64 delta, u64 mul_frac)
+ 	u64 product, unused;
+ 
+ 	__asm__ (
+-		"mul %3"
++		"mulq %3"
+ 		: "=d" (product), "=a" (unused) : "1" (delta), "rm" ((u64)mul_frac) );
+ 
+ 	return product;
+-- 
+2.7.4
+