From: Baoquan He <bhe@redhat.com>
To: Jisheng Zhang <jszhang@kernel.org>
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
Date: Wed, 19 Jan 2022 16:08:59 +0800 [thread overview]
Message-ID: <20220119080859.GB4977@MiWiFi-R3L-srv> (raw)
In-Reply-To: <YebK70Sx4w8zLfj/@xhacker>
On 01/18/22 at 10:13pm, Jisheng Zhang wrote:
> 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
Glad to know the fix. While, sometime the ifdeffery is necessary. I am
sorry about the one in riscv and you have fixed, it's truly a bug . But,
the increasing compile coverage at below you tried to make, it may cause
issue. Please see below my comment.
>
> >
> > 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.
This is what I am worried about. Before, if CONFIG_KEXEC_CORE is
unset, those relevant codes are not compiled in. I can't see what
benefit is brought in if compiled in the unneeded code block. Do I miss
anything?
next prev parent reply other threads:[~2022-01-19 8:09 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-06 16:05 [PATCH v2 0/5] kexec: use IS_ENABLED(CONFIG_KEXEC_CORE) instead of #ifdef Jisheng Zhang
2021-12-06 16:05 ` [PATCH v2 1/5] kexec: make crashk_res, crashk_low_res and crash_notes symbols always visible Jisheng Zhang
2021-12-06 16:05 ` [PATCH v2 2/5] riscv: mm: init: use IS_ENABLED(CONFIG_KEXEC_CORE) instead of #ifdef Jisheng Zhang
2022-01-11 17:29 ` Palmer Dabbelt
2021-12-06 16:05 ` [PATCH v2 3/5] x86/setup: " Jisheng Zhang
2021-12-06 16:05 ` [PATCH v2 4/5] arm64: mm: " Jisheng Zhang
2021-12-06 16:05 ` [PATCH v2 5/5] arm: " Jisheng Zhang
2022-01-16 13:38 ` [PATCH v2 0/5] kexec: " Baoquan He
2022-01-18 14:13 ` Jisheng Zhang
2022-01-19 8:08 ` Baoquan He [this message]
2022-01-19 8:52 ` Alexandre Ghiti
2022-01-19 9:33 ` Baoquan He
2022-01-19 11:44 ` Jisheng Zhang
2022-01-20 9:45 ` Baoquan He
2022-01-20 9:50 ` Baoquan He
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