Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Fri, 14 Jul 2023 11:01:34 +0300
From:   Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To:     Yury Norov <yury.norov@gmail.com>
Cc:     Alexander Potapenko <glider@google.com>, catalin.marinas@arm.com,
        will@kernel.org, pcc@google.com, andreyknvl@gmail.com,
        linux@rasmusvillemoes.dk, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, eugenis@google.com
Subject: Re: [v2 3/5] arm64: mte: implement CONFIG_ARM64_MTE_COMP
Message-ID: <ZLEA3oxst2FBDWhC@smile.fi.intel.com>
References: <20230713125706.2884502-1-glider@google.com>
 <20230713125706.2884502-4-glider@google.com>
 <ZLAzG+Ue3JqDM/F3@smile.fi.intel.com>
 <ZLBQCFbBOaBUTQmB@yury-ThinkPad>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <ZLBQCFbBOaBUTQmB@yury-ThinkPad>
Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo
Precedence: bulk

On Thu, Jul 13, 2023 at 12:27:15PM -0700, Yury Norov wrote:

...

> > > +	void *storage = ea0_storage(handle);
> > > +	int size = ea0_storage_size(handle);

> > > +	if (!handle || !storage)
> > > +		return;
> > 
> > You use handle before this check. Haven't you run static analysers?
> 
> This approach is called 'defensive programming' as I learned from
> previous iteration.

No, this approach called "let compiler optimize the check away". :-)

When compiler sees something like

	TYPE bar = MACRO(foo); // FUNC(foo);

	if (!foo)
		blalblabla;

the conditional can be eliminated as the optimizer thinks the way "okay,
developer already _used_ the foo in some code, it means it can't not be NULL,
let's drop a dead code".

(Yes, I know what defensive programming means and we actually quite rarely
 use it in the kernel for the internal APIs)

-- 
With Best Regards,
Andy Shevchenko