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Date:   Tue, 18 Jan 2022 22:13:03 +0800
From:   Jisheng Zhang <jszhang@kernel.org>
To:     Baoquan He <bhe@redhat.com>
Cc:     Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        hpa@zytor.com, Eric Biederman <ebiederm@xmission.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-riscv@lists.infradead.org, kexec@lists.infradead.org,
        Alexandre ghiti <alex@ghiti.fr>
Subject: Re: [PATCH v2 0/5] kexec: use IS_ENABLED(CONFIG_KEXEC_CORE) instead
 of #ifdef
Message-ID: <YebK70Sx4w8zLfj/@xhacker>
References: <20211206160514.2000-1-jszhang@kernel.org>
 <20220116133847.GE2388@MiWiFi-R3L-srv>
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On Sun, Jan 16, 2022 at 09:38:47PM +0800, Baoquan He wrote:
> Hi Jisheng,

Hi Baoquan,

> 
> On 12/07/21 at 12:05am, Jisheng Zhang wrote:
> > Replace the conditional compilation using "#ifdef CONFIG_KEXEC_CORE"
> > by a check for "IS_ENABLED(CONFIG_KEXEC_CORE)", to simplify the code
> > and increase compile coverage.
> 
> I go through this patchset, You mention the benefits it brings are
> 1) simplity the code;
> 2) increase compile coverage;
> 
> For benefit 1), it mainly removes the dummy function in x86, arm and
> arm64, right?

Another benefit: remove those #ifdef #else #endif usage. Recently, I
fixed a bug due to lots of "#ifdefs":
http://lists.infradead.org/pipermail/linux-riscv/2021-December/010607.html

> 
> For benefit 2), increasing compile coverage, could you tell more how it
> achieves and why it matters? What if people disables CONFIG_KEXEC_CORE in
> purpose? Please forgive my poor compiling knowledge.

Just my humble opinion, let's compare the code::

#ifdef CONFIG_KEXEC_CORE

code block A;

#endif

If KEXEC_CORE is disabled, code block A won't be compiled at all, the
preprocessor will remove code block A;

If we convert the code to:

if (IS_ENABLED(CONFIG_KEXEC_CORE)) {
	code block A;
}

Even if KEXEC_CORE is disabled, code block A is still compiled.

Thanks