linux-kernel - Re: [PATCH] KVM: selftests: x86: Avoid using SSE/AVX instructions

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Message-ID: <9a160e3d-501b-4759-9067-17cd822617ec@sirena.org.uk>
Date: Mon, 21 Oct 2024 19:32:13 +0100
From: Mark Brown <broonie@...nel.org>
To: Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
	Sean Christopherson <seanjc@...gle.com>,
	Jan Richter <jarichte@...hat.com>, linux-kernel@...r.kernel.org,
	Aishwarya.TCV@....com
Subject: Re: [PATCH] KVM: selftests: x86: Avoid using SSE/AVX instructions

On Fri, Sep 20, 2024 at 05:44:22PM +0200, Vitaly Kuznetsov wrote:

> Some distros switched gcc to '-march=x86-64-v3' by default and while it's
> hard to find a CPU which doesn't support it today, many KVM selftests fail
> with

This patch, which is queued in -next as 9a400068a1586bc4 targeted as a
fix, breaks the build on non-x86 architectures:

aarch64-linux-gnu-gcc -D_GNU_SOURCE=  -Wall -Wstrict-prototypes -Wuninitialized 
-O2 -g -std=gnu99 -Wno-gnu-variable-sized-type-not-at-end -MD -MP -DCONFIG_64BIT
 -fno-builtin-memcmp -fno-builtin-memcpy -fno-builtin-memset -fno-builtin-strnlen -fno-stack-protector -fno-PIE -I/build/stage/linux/tools/testing/selftests/../../../tools/include -I/build/stage/linux/tools/testing/selftests/../../../tools/arch/arm64/include -I/build/stage/linux/tools/testing/selftests/../../../usr/include/ -Iinclude -Iaarch64 -Iinclude/aarch64 -I ../rseq -I..  -march=x86-64-v2 -isystem /build/stage/build-work/usr/include -I/build/stage/linux/tools/testing/selftests/../../../tools/arch/arm64/include/generated/   -c aarch64/aarch32_id_regs.c -o /build/stage/build-work/kselftest/kvm/aarch64/aarch32_id_regs.o
cc1: error: unknown value ‘x86-64-v2’ for ‘-march’

This is because:

> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index 48d32c5aa3eb..3f1b24ed7245 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -238,6 +238,7 @@ CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \
>  	-fno-stack-protector -fno-PIE -I$(LINUX_TOOL_INCLUDE) \
>  	-I$(LINUX_TOOL_ARCH_INCLUDE) -I$(LINUX_HDR_PATH) -Iinclude \
>  	-I$(<D) -Iinclude/$(ARCH_DIR) -I ../rseq -I.. $(EXTRA_CFLAGS) \
> +	-march=x86-64-v2 \
>  	$(KHDR_INCLUDES)
>  ifeq ($(ARCH),s390)
>  	CFLAGS += -march=z10

unconditionally sets an architecture specific flag which is obviously
not going to work on anything except x86.  This should be set under an
architecture check like the similar S/390 flag that can be seen in the
context for the diff.

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