Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20200103033929.4956-1-zhenzhong.duan@gmail.com>
 <20200109184055.GI5603@zn.tnic> <20200109204638.GA523773@rani.riverdale.lan>
In-Reply-To: <20200109204638.GA523773@rani.riverdale.lan>
From:   Zhenzhong Duan <zhenzhong.duan@gmail.com>
Date:   Fri, 10 Jan 2020 10:27:02 +0800
Message-ID: <CAFH1YnNA9qfM4tPzKKDaQD6DPxnE=tJsB7AUZQBohDTW3zm=Xg@mail.gmail.com>
Subject: Re: [PATCH v2] x86/boot/KASLR: Fix unused variable warning
To:     Arvind Sankar <nivedita@alum.mit.edu>
Cc:     Borislav Petkov <bp@alien8.de>, linux-kernel@vger.kernel.org,
        x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@suse.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Chao Fan <fanc.fnst@cn.fujitsu.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Jan 10, 2020 at 4:46 AM Arvind Sankar <nivedita@alum.mit.edu> wrote=
:
>
> On Thu, Jan 09, 2020 at 07:40:55PM +0100, Borislav Petkov wrote:
> > On Fri, Jan 03, 2020 at 11:39:29AM +0800, Zhenzhong Duan wrote:
> > > Local variable 'i' is referenced only when CONFIG_MEMORY_HOTREMOVE an=
d
> > > CONFIG_ACPI are defined, but definition of variable 'i' is out of gua=
rd.
> > > If any of the two macros is undefined, below warning triggers during
> > > build, fix it by moving 'i' in the guard.
> > >
> > > arch/x86/boot/compressed/kaslr.c:698:6: warning: unused variable =E2=
=80=98i=E2=80=99 [-Wunused-variable]
> >
> > How do you trigger this?
> >
> > I have:
> >
> > $  grep -E "(CONFIG_MEMORY_HOTREMOVE|CONFIG_ACPI)" .config
> > # CONFIG_ACPI is not set
> >
> > but no warning. Neither with gcc 8 nor with gcc 9.
> >
> > --
> > Regards/Gruss,
> >     Boris.
> >
> > https://people.kernel.org/tglx/notes-about-netiquette
>
> The boot/compressed Makefile resets KBUILD_CFLAGS.  Following hack and
> building with W=3D1 shows it, or just add -Wunused in there.
>
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed=
/Makefile
> index 56aa5fa0a66b..791c0d5a952a 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -35,6 +35,9 @@ KBUILD_CFLAGS +=3D $(cflags-y)
>  KBUILD_CFLAGS +=3D -mno-mmx -mno-sse
>  KBUILD_CFLAGS +=3D $(call cc-option,-ffreestanding)
>  KBUILD_CFLAGS +=3D $(call cc-option,-fno-stack-protector)
> +
> +include scripts/Makefile.extrawarn
> +
>  KBUILD_CFLAGS +=3D $(call cc-disable-warning, address-of-packed-member)
>  KBUILD_CFLAGS +=3D $(call cc-disable-warning, gnu)
>  KBUILD_CFLAGS +=3D -Wno-pointer-sign

Yes. Will you send this formally? Not clear if there is other reason making
KBUILD_CFLAGS for arch/x86/boot/compressed different from other part.

Regards
Zhenzhong