linux-kernel - Re: [PATCH] [v2] x86: apic: avoid -Wshadow warning in header

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Message-ID: <20201029165611.GA2557691@rani.riverdale.lan>
Date:   Thu, 29 Oct 2020 12:56:11 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Arnd Bergmann' <arnd@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "x86@...nel.org" <x86@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: Re: [PATCH] [v2] x86: apic: avoid -Wshadow warning in header

On Thu, Oct 29, 2020 at 03:05:31PM +0000, David Laight wrote:
> From: Arnd Bergmann
> > Sent: 28 October 2020 21:21
> > 
> > From: Arnd Bergmann <arnd@...db.de>
> > 
> > There are hundreds of warnings in a W=2 build about a local
> > variable shadowing the global 'apic' definition:
> > 
> > arch/x86/kvm/lapic.h:149:65: warning: declaration of 'apic' shadows a global declaration [-Wshadow]
> > 
> > Avoid this by renaming the global 'apic' variable to the more descriptive
> > 'x86_system_apic'. It was originally called 'genapic', but both that
> > and the current 'apic' seem to be a little overly generic for a global
> > variable.
> > 
> > Fixes: c48f14966cc4 ("KVM: inline kvm_apic_present() and kvm_lapic_enabled()")
> > Fixes: c8d46cf06dc2 ("x86: rename 'genapic' to 'apic'")
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > ---
> > v2: rename the global instead of the local variable in the header
> ...
> > diff --git a/arch/x86/hyperv/hv_apic.c b/arch/x86/hyperv/hv_apic.c
> > index 284e73661a18..33e2dc78ca11 100644
> > --- a/arch/x86/hyperv/hv_apic.c
> > +++ b/arch/x86/hyperv/hv_apic.c
> > @@ -259,14 +259,14 @@ void __init hv_apic_init(void)
> >  		/*
> >  		 * Set the IPI entry points.
> >  		 */
> > -		orig_apic = *apic;
> > -
> > -		apic->send_IPI = hv_send_ipi;
> > -		apic->send_IPI_mask = hv_send_ipi_mask;
> > -		apic->send_IPI_mask_allbutself = hv_send_ipi_mask_allbutself;
> > -		apic->send_IPI_allbutself = hv_send_ipi_allbutself;
> > -		apic->send_IPI_all = hv_send_ipi_all;
> > -		apic->send_IPI_self = hv_send_ipi_self;
> > +		orig_apic = *x86_system_apic;
> > +
> > +		x86_system_apic->send_IPI = hv_send_ipi;
> > +		x86_system_apic->send_IPI_mask = hv_send_ipi_mask;
> > +		x86_system_apic->send_IPI_mask_allbutself = hv_send_ipi_mask_allbutself;
> > +		x86_system_apic->send_IPI_allbutself = hv_send_ipi_allbutself;
> > +		x86_system_apic->send_IPI_all = hv_send_ipi_all;
> > +		x86_system_apic->send_IPI_self = hv_send_ipi_self;
> >  	}
> > 
> >  	if (ms_hyperv.hints & HV_X64_APIC_ACCESS_RECOMMENDED) {
> > @@ -285,10 +285,10 @@ void __init hv_apic_init(void)
> >  		 */
> >  		apic_set_eoi_write(hv_apic_eoi_write);
> >  		if (!x2apic_enabled()) {
> > -			apic->read      = hv_apic_read;
> > -			apic->write     = hv_apic_write;
> > -			apic->icr_write = hv_apic_icr_write;
> > -			apic->icr_read  = hv_apic_icr_read;
> > +			x86_system_apic->read      = hv_apic_read;
> > +			x86_system_apic->write     = hv_apic_write;
> > +			x86_system_apic->icr_write = hv_apic_icr_write;
> > +			x86_system_apic->icr_read  = hv_apic_icr_read;
> >  		}
> 
> For those two just add:
> 	struct apic *apic = x86_system_apic;
> before all the assignments.
> Less churn and much better code.
> 

Why would it be better code?