linux-kernel - Re: [PATCH] KVM: x86/i8259: Remove a dead store of irq in a conditional block

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Date:   Tue, 1 Mar 2022 16:01:12 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86/i8259: Remove a dead store of irq in a
 conditional block

On Tue, Mar 01, 2022, Like Xu wrote:
> From: Like Xu <likexu@...cent.com>
> 
> The [clang-analyzer-deadcode.DeadStores] helper reports
> that the value stored to 'irq' is never read.
> 
> Signed-off-by: Like Xu <likexu@...cent.com>

Reviewed-by: Sean Christopherson <seanjc@...gle.com>

> ---
> Note: not sure if "irq2 + 8" should be needed for "s->pics[0].irq_base + irq"

Nope, IRQ 2 is used to cascade PIC controllers, and the two controllers have separate
vector offsets/bases.  The code was there in the original commit, 85f455f7ddbe ("KVM:
Add support for in-kernel PIC emulation"), best guess is that it was leftover from
development, e.g. maybe a flawed assumption the the second PIC's vector was simply +8?