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From: Daniel Palmer <daniel@0x0f.com>
To: Romain Perier <romain.perier@gmail.com>
Cc: Colin King <colin.king@canonical.com>,
	Daniel Palmer <daniel@thingy.jp>,
	Alessandro Zummo <a.zummo@towertech.it>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	Nobuhiro Iwamatsu <iwamatsu@nigauri.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	linux-rtc@vger.kernel.org, kernel-janitors@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH][next] rtc: msc313: Fix unintentional sign extension issue on left shift of a u16
Date: Wed, 29 Sep 2021 21:56:36 +0900	[thread overview]
Message-ID: <CAFr9PXna7YsYnfdtu1jvJhkVSX0SiyixYr_bTsx3tDepeHqcMg@mail.gmail.com> (raw)
In-Reply-To: <CABgxDoLPTcRbZZgAdJ9+=9OG+a=F59x9SQ9HvQkVvGmkDjO6-A@mail.gmail.com>

Hi Romain,

On Tue, 28 Sept 2021 at 22:55, Romain Perier <romain.perier@gmail.com> wrote:
>
> Hi,
>
> Le mar. 28 sept. 2021 à 15:31, Daniel Palmer <daniel@0x0f.com> a écrit :
> The crazy stuff being, I ran rtctest from selftests and rtc-range (1)
> that tests a variety
> of dates including 2038 and 2106 for example. Both tests passed :) (probably
> because *this case* specifically did not happen while running the test)

I suspect it works because for reading the time because seconds is a
u32 not unsigned long like the other functions.
So if the high word of the register is read, is promoted to a wider
type and sign extended it doesn't actually matter because it gets
truncated to 32 bits so the sign extended part is gone.

Cheers,

Daniel

WARNING: multiple messages have this Message-ID (diff)
From: Daniel Palmer <daniel@0x0f.com>
To: Romain Perier <romain.perier@gmail.com>
Cc: Colin King <colin.king@canonical.com>,
	Daniel Palmer <daniel@thingy.jp>,
	 Alessandro Zummo <a.zummo@towertech.it>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	 Nobuhiro Iwamatsu <iwamatsu@nigauri.org>,
	 linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	linux-rtc@vger.kernel.org, kernel-janitors@vger.kernel.org,
	 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH][next] rtc: msc313: Fix unintentional sign extension issue on left shift of a u16
Date: Wed, 29 Sep 2021 21:56:36 +0900	[thread overview]
Message-ID: <CAFr9PXna7YsYnfdtu1jvJhkVSX0SiyixYr_bTsx3tDepeHqcMg@mail.gmail.com> (raw)
In-Reply-To: <CABgxDoLPTcRbZZgAdJ9+=9OG+a=F59x9SQ9HvQkVvGmkDjO6-A@mail.gmail.com>

Hi Romain,

On Tue, 28 Sept 2021 at 22:55, Romain Perier <romain.perier@gmail.com> wrote:
>
> Hi,
>
> Le mar. 28 sept. 2021 à 15:31, Daniel Palmer <daniel@0x0f.com> a écrit :
> The crazy stuff being, I ran rtctest from selftests and rtc-range (1)
> that tests a variety
> of dates including 2038 and 2106 for example. Both tests passed :) (probably
> because *this case* specifically did not happen while running the test)

I suspect it works because for reading the time because seconds is a
u32 not unsigned long like the other functions.
So if the high word of the register is read, is promoted to a wider
type and sign extended it doesn't actually matter because it gets
truncated to 32 bits so the sign extended part is gone.

Cheers,

Daniel

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

  reply	other threads:[~2021-09-29 12:54 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-28 12:39 [PATCH][next] rtc: msc313: Fix unintentional sign extension issue on left shift of a u16 Colin King
2021-09-28 12:39 ` Colin King
2021-09-28 13:31 ` Daniel Palmer
2021-09-28 13:31   ` Daniel Palmer
2021-09-28 13:34   ` Colin Ian King
2021-09-28 13:34     ` Colin Ian King
2021-09-28 13:54   ` Romain Perier
2021-09-28 13:54     ` Romain Perier
2021-09-29 12:56     ` Daniel Palmer [this message]
2021-09-29 12:56       ` Daniel Palmer

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