linux-kernel - Re: [PATCH] selftests: kvm/x86: Fix the warning in lib/x86

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Message-ID: <d4b47a8e-77f2-eef2-2245-bdc7eaf8f57f@redhat.com>
Date:   Wed, 19 Jan 2022 19:37:50 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jinrong Liang <ljr.kernel@...il.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Jinrong Liang <cloudliang@...cent.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests: kvm/x86: Fix the warning in
 lib/x86_64/processor.c

On 1/19/22 15:03, Jinrong Liang wrote:
> From: Jinrong Liang <cloudliang@...cent.com>
> 
> The following warning appears when executing
> make -C tools/testing/selftests/kvm
> 
> In file included from lib/x86_64/processor.c:11:
> lib/x86_64/processor.c: In function ':
> include/x86_64/processor.h:290:2: warning: 'ecx' may be used uninitialized in this
> function [-Wmaybe-uninitialized]
>    asm volatile("cpuid"
>    ^~~
> lib/x86_64/processor.c:1523:21: note: 'ecx' was declared here
>    uint32_t eax, ebx, ecx, edx, max_ext_leaf;
> 
> Just initialize ecx to remove this warning.
> 
> Fixes: c8cc43c1eae2 ("selftests: KVM: avoid failures due to reserved
> HyperTransport region")
> 
> Signed-off-by: Jinrong Liang <cloudliang@...cent.com>
> ---
>   tools/testing/selftests/kvm/lib/x86_64/processor.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> index 59dcfe1967cc..4a4c7945cf3e 100644
> --- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
> +++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> @@ -1520,7 +1520,7 @@ unsigned long vm_compute_max_gfn(struct kvm_vm *vm)
>   {
>   	const unsigned long num_ht_pages = 12 << (30 - vm->page_shift); /* 12 GiB */
>   	unsigned long ht_gfn, max_gfn, max_pfn;
> -	uint32_t eax, ebx, ecx, edx, max_ext_leaf;
> +	uint32_t eax, ebx, ecx = 0, edx, max_ext_leaf;
>   
>   	max_gfn = (1ULL << (vm->pa_bits - vm->page_shift)) - 1;
>   

A separate assignment of "ecx = 0" is slightly more conforming to the 
coding standards.  Queued nevertheless, thanks.

Paolo