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

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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>
This commit is contained in:
Thomas Petazzoni 2017-05-08 22:41:43 +02:00
parent abb825bd6b
commit bdadcf593d
1 changed files with 35 additions and 0 deletions
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35
package/kvm-unit-tests/0001-x86-hyperv_clock-be-explicit-about-mul-instruction-d.patch Normal file
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@ -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