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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
Date: Fri, 14 Jul 2023 11:01:34 +0300	[thread overview]
Message-ID: <ZLEA3oxst2FBDWhC@smile.fi.intel.com> (raw)
In-Reply-To: <ZLBQCFbBOaBUTQmB@yury-ThinkPad>

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



_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

WARNING: multiple messages have this Message-ID (diff)
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
Date: Fri, 14 Jul 2023 11:01:34 +0300	[thread overview]
Message-ID: <ZLEA3oxst2FBDWhC@smile.fi.intel.com> (raw)
In-Reply-To: <ZLBQCFbBOaBUTQmB@yury-ThinkPad>

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



  reply	other threads:[~2023-07-14  8:02 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-13 12:57 [v2 0/5] Implement MTE tag compression for swapped pages Alexander Potapenko
2023-07-13 12:57 ` Alexander Potapenko
2023-07-13 12:57 ` [v2 1/5] lib/bitmap: add bitmap_{set,get}_value_unaligned() Alexander Potapenko
2023-07-13 12:57   ` Alexander Potapenko
2023-07-13 17:28   ` Andy Shevchenko
2023-07-13 17:28     ` Andy Shevchenko
2023-07-13 18:05     ` Alexander Potapenko
2023-07-13 18:05       ` Alexander Potapenko
2023-07-14  8:04       ` Andy Shevchenko
2023-07-14  8:04         ` Andy Shevchenko
2023-07-14 11:19         ` William Breathitt Gray
2023-07-14 11:19           ` William Breathitt Gray
2023-07-14 11:28           ` Andy Shevchenko
2023-07-14 11:28             ` Andy Shevchenko
2023-07-14 12:07             ` Alexander Potapenko
2023-07-14 12:07               ` Alexander Potapenko
2023-07-14 12:30               ` Andy Shevchenko
2023-07-14 12:30                 ` Andy Shevchenko
2023-07-13 12:57 ` [v2 2/5] lib/test_bitmap: add tests for bitmap_{set,get}_value_unaligned Alexander Potapenko
2023-07-13 12:57   ` Alexander Potapenko
2023-07-13 12:57 ` [v2 3/5] arm64: mte: implement CONFIG_ARM64_MTE_COMP Alexander Potapenko
2023-07-13 12:57   ` Alexander Potapenko
2023-07-13 16:37   ` Alexander Potapenko
2023-07-13 16:37     ` Alexander Potapenko
2023-07-13 17:23   ` Andy Shevchenko
2023-07-13 17:23     ` Andy Shevchenko
2023-07-13 19:27     ` Yury Norov
2023-07-13 19:27       ` Yury Norov
2023-07-14  8:01       ` Andy Shevchenko [this message]
2023-07-14  8:01         ` Andy Shevchenko
2023-07-14  9:25     ` Alexander Potapenko
2023-07-14  9:25       ` Alexander Potapenko
2023-07-14 10:47       ` Andy Shevchenko
2023-07-14 10:47         ` Andy Shevchenko
2023-07-14 11:17         ` Alexander Potapenko
2023-07-14 11:17           ` Alexander Potapenko
2023-07-13 12:57 ` [v2 4/5] arm64: mte: add a test for MTE tags compression Alexander Potapenko
2023-07-13 12:57   ` Alexander Potapenko
2023-07-13 12:57 ` [v2 5/5] arm64: mte: add compression support to mteswap.c Alexander Potapenko
2023-07-13 12:57   ` Alexander Potapenko

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