linux-kernel - Re: [v8] misc: pci_endpoint_test: Fix overflow of bar

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Message-ID: <Z31O8B14sKd5eac-@ryzen>
Date: Tue, 7 Jan 2025 16:57:36 +0100
From: Niklas Cassel <cassel@...nel.org>
To: Hans Zhang <18255117159@....com>
Cc: manivannan.sadhasivam@...aro.org, kw@...ux.com, kishon@...nel.org,
	arnd@...db.de, gregkh@...uxfoundation.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	rockswang7@...il.com
Subject: Re: [v8] misc: pci_endpoint_test: Fix overflow of bar_size

On Tue, Jan 07, 2025 at 11:44:21PM +0800, Hans Zhang wrote:
> 
> 
> On 2025/1/7 19:47, Niklas Cassel wrote:
> 
> Hi Niklas,
> 
> > The error:
> > drivers/misc/pci_endpoint_test.c:315: undefined reference to `__udivmoddi4'
> > sounds like the compiler is using a specialized instruction to do both div
> > and mod in one. By removing the mod in patch 1/2, I expect that patch 2/2
> > will no longer get this error.
> 
> The __udivmoddi4 may be the way div and mod are combined.
> 
> Delete remain's patch 1/2 according to your suggestion. I compiled it as a
> KO module for an experiment.
> 
> There are still __udivdi3 errors, so the do_div API must be used.

Ok. Looking at do_div(), it seems to be the correct API to use
for this problem. Just change bar_size type to u64 (instead of casting)
and use do_div() ? That is how it is seems to be used in other drivers.

I still think that a patch that removes the "remainder" code is a good
cleanup, so please send it as patch 1/2, you can be the author, just add:
Suggested-by: Niklas Cassel <cassel@...nel.org>


Kind regards,
Niklas