Re: [PATCH v2 0/5] kexec: use IS_ENABLED(CONFIG_KEXEC_CORE) instead of #ifdef

[Jisheng Zhang]

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