linux-kernel - Re: [PATCH] [v3] x86: kvm: avoid -Wsometimes-uninitized warning

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Date:   Fri, 12 Jul 2019 10:44:54 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Roman Kagan <rkagan@...tuozzo.com>,
        Liran Alon <liran.alon@...cle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH] [v3] x86: kvm: avoid -Wsometimes-uninitized warning

On Fri, Jul 12, 2019 at 04:13:09PM +0200, Arnd Bergmann wrote:
> Clang notices a code path in which some variables are never
> initialized, but fails to figure out that this can never happen
> on i386 because is_64_bit_mode() always returns false.
> 
> arch/x86/kvm/hyperv.c:1610:6: error: variable 'ingpa' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
>         if (!longmode) {
>             ^~~~~~~~~
> arch/x86/kvm/hyperv.c:1632:55: note: uninitialized use occurs here
>         trace_kvm_hv_hypercall(code, fast, rep_cnt, rep_idx, ingpa, outgpa);
>                                                              ^~~~~
> arch/x86/kvm/hyperv.c:1610:2: note: remove the 'if' if its condition is always true
>         if (!longmode) {
>         ^~~~~~~~~~~~~~~
> arch/x86/kvm/hyperv.c:1595:18: note: initialize the variable 'ingpa' to silence this warning
>         u64 param, ingpa, outgpa, ret = HV_STATUS_SUCCESS;
>                         ^
>                          = 0
> arch/x86/kvm/hyperv.c:1610:6: error: variable 'outgpa' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
> arch/x86/kvm/hyperv.c:1610:6: error: variable 'param' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
> 
> Flip the condition around to avoid the conditional execution on i386.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>