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From: Finn Thain <fthain@linux-m68k.org>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Sascha Hauer" <kernel@pengutronix.de>,
	linux-m68k <linux-m68k@lists.linux-m68k.org>
Subject: Re: [PATCH 1/5] nubus: Simplify check in remove callback
Date: Tue, 27 Jul 2021 20:19:35 +1000 (AEST)	[thread overview]
Message-ID: <194b351c-bae-27a-1875-9ad3c47292e@linux-m68k.org> (raw)
In-Reply-To: <CAMuHMdX=K4S3Yd_ybd5C3e40XefMf5kHs1tWs1+VKTgiWEWEDg@mail.gmail.com>

[-- Attachment #1: Type: text/plain, Size: 886 bytes --]

On Tue, 27 Jul 2021, Geert Uytterhoeven wrote:

> On Tue, Jul 27, 2021 at 11:50 AM Finn Thain <fthain@linux-m68k.org> wrote:
> > On Tue, 27 Jul 2021, Uwe Kleine-König wrote:
> > > Apart from that, the compiler might already assume dev->driver being 
> > > non-NULL after to_nubus_driver(dev->driver) was called.
> >
> > I don't understand how a compiler can make that assumption. But then, 
> > I don't know why compilers do a lot of the things they do...
> 
> It is one of those recent optimizations people have been complaining 
> about.  Once you have dereferenced a pointer, compilers may remove all 
> further NULL-checks, assuming they can't happen, as the code would have 
> crashed anyway before due to the dereference.

But that's the point -- there is no dereference, just pointer arithmetic.

> Good luck running on bare metal with RAM at zero ;-)

Quite.

  reply	other threads:[~2021-07-27 10:19 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-27  8:08 [PATCH 0/5] Some cleanups after making bus_type::remove return void Uwe Kleine-König
2021-07-27  8:08 ` [PATCH 1/5] nubus: Simplify check in remove callback Uwe Kleine-König
2021-07-27  9:50   ` Finn Thain
2021-07-27 10:07     ` Geert Uytterhoeven
2021-07-27 10:19       ` Finn Thain [this message]
2021-07-27 11:42     ` Uwe Kleine-König
2021-07-31 10:32       ` Finn Thain
2021-07-31 12:05         ` Uwe Kleine-König
2021-07-27  8:08 ` [PATCH 2/5] nubus: Make struct nubus_driver::remove return void Uwe Kleine-König
2021-07-27  9:47   ` Finn Thain
2021-07-27  8:08 ` [PATCH 3/5] sh: superhyway: Simplify check in remove callback Uwe Kleine-König
2021-07-27  8:08 ` [PATCH 4/5] zorro: Simplify " Uwe Kleine-König
2021-07-27  8:08 ` [PATCH 5/5] zorro: Drop useless (and hardly used) .driver member in struct zorro_dev Uwe Kleine-König

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