linux-kernel - Re: [PATCH v2] KVM: selftests: Compile code with warnings enabled

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Date:   Mon, 20 May 2019 12:00:44 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Thomas Huth <thuth@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Peter Xu <peterx@...hat.com>
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        linux-kselftest@...r.kernel.org, kvm@...r.kernel.org,
        Shuah Khan <shuah@...nel.org>,
        Andrew Jones <drjones@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: selftests: Compile code with warnings enabled

On 17/05/19 12:07, Thomas Huth wrote:
> 
> lib/ucall.c: In function ‘get_ucall’:
> lib/ucall.c:145:3: warning: dereferencing type-punned pointer will break
> strict-aliasing rules [-Wstrict-aliasing]
>    gva = *(vm_vaddr_t *)run->mmio.data;
> 
> x86_64/vmx_set_nested_state_test.c: In function
> ‘set_revision_id_for_vmcs12’:
> x86_64/vmx_set_nested_state_test.c:78:2: warning: dereferencing
> type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
>   *(u32 *)(state->data) = vmcs12_revision;
> 
> ... how do we want to handle such spots in the kvm selftest code?
> Compile with -fno-strict-aliasing? Or fix it with type-punning through
> unions?

I would use memcpy.  I'll send a patch shortly.

Paolo