[Buildroot] [PATCH] kvm-unit-tests: fix build on x86-64 with specific gcc versions

[Buildroot] [PATCH] kvm-unit-tests: fix build on x86-64 with specific gcc versions

[Thomas Petazzoni]

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>
---
 ...clock-be-explicit-about-mul-instruction-d.patch | 35 ++++++++++++++++++++++
 1 file changed, 35 insertions(+)
 create mode 100644 package/kvm-unit-tests/0001-x86-hyperv_clock-be-explicit-about-mul-instruction-d.patch

diff --git a/package/kvm-unit-tests/0001-x86-hyperv_clock-be-explicit-about-mul-instruction-d.patch b/package/kvm-unit-tests/0001-x86-hyperv_clock-be-explicit-about-mul-instruction-d.patch
new file mode 100644
index 0000000..c8ee6b1
--- /dev/null
+++ b/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
+
-- 
2.7.4

[Buildroot] [PATCH] kvm-unit-tests: fix build on x86-64 with specific gcc versions

[Peter Korsgaard]

>>>>> "Thomas" == Thomas Petazzoni <thomas.petazzoni@free-electrons.com> writes:

 > 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>

Committed to 2017.02.x, thanks.

-- 
Bye, Peter Korsgaard

[Buildroot] [PATCH] kvm-unit-tests: fix build on x86-64 with specific gcc versions

[Thomas Petazzoni]

Hello,

On Mon,  8 May 2017 22:41:43 +0200, Thomas Petazzoni wrote:

>  ...clock-be-explicit-about-mul-instruction-d.patch | 35 ++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
>  create mode 100644 package/kvm-unit-tests/0001-x86-hyperv_clock-be-explicit-about-mul-instruction-d.patch

This patch has been accepted upstream:
https://git.kernel.org/pub/scm/virt/kvm/kvm-unit-tests.git/commit/?id=45276b5860522921c77fb3ccc1458ff5f223c3c6.

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com