RE: [PATCH v3 3/4] drm/mediatek: Add casting before assign

[David Laight <David.Laight@ACULAB.COM>]

From: Jason-JH Lin
> Sent: 14 July 2023 07:46
> 
> Hi CK,
> 
> Thanks for the reviews.
> 
> On Fri, 2023-07-14 at 05:45 +0000, CK Hu (胡俊光) wrote:
> > Hi, Jason:
> >
> > On Wed, 2023-06-21 at 18:22 +0800, Jason-JH.Lin wrote:
> > > 1. Add casting before assign to avoid the unintentional integer
> > >    overflow or unintended sign extension.
> > > 2. Add a int varriable for multiplier calculation instead of
> > > calculating
> > >    different types multiplier with dma_addr_t varriable directly.
> >
> > I agree with these modification, but the title does not match the
> > modification.
> >
> > Regards,
> > CK
> 
> I'll change the title and commit msg at the next version below:
> 
> Fix unintentional integer overflow in multiplying different types
> 
> 1. Instead of multiplying 2 variable of different types. Change to
> assign a value of one variable and then multiply the other variable.
> 
> 2. Add a int variable for multiplier calculation instead of calculating
> different types multiplier with dma_addr_t variable directly.

I'm pretty sure the patch makes absolutely no difference.
In C all arithmetic is done with char/short (inc. unsigned)
promoted to int.

So the only likely overflow is if the values exceed 2^31.
Since the temporaries you are using are 'int' this isn't true.

	David

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