linux-kernel - RE: Re：Re: [PATCH] powerpc: Fix a bug in __div64

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Date:   Mon, 24 Aug 2020 15:05:13 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Guohua Zhong' <zhongguohua1@...wei.com>,
        "paubert@...m.es" <paubert@...m.es>
CC:     "christophe.leroy@...roup.eu" <christophe.leroy@...roup.eu>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "nixiaoming@...wei.com" <nixiaoming@...wei.com>,
        "paulus@...ba.org" <paulus@...ba.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "wangle6@...wei.com" <wangle6@...wei.com>
Subject: RE: Re：Re: [PATCH] powerpc: Fix a bug in __div64_32 if divisor is zero

From: Guohua Zhong
> Sent: 24 August 2020 14:26
> 
> >> >In generic version in lib/math/div64.c, there is no checking of 'base'
> >> >either.
> >> >Do we really want to add this check in the powerpc version only ?
> >>
> >> >The only user of __div64_32() is do_div() in
> >> >include/asm-generic/div64.h. Wouldn't it be better to do the check there ?
> >>
> >> >Christophe
> >>
> >> Yet, I have noticed that there is no checking of 'base' in these functions.
> >> But I am not sure how to check is better.As we know that the result is
> >> undefined when divisor is zero. It maybe good to print error and dump stack.

I thought that the onus was put on the caller to avoid divide by zero.

On x86 divide by zero causes an exception which (I'm pretty sure)
leads to a oops/panic.

	David

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