linux-kernel - Re: [PATCH 1/4] EDAC: Fix calculation of returned address and next offset in edac_align

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Date:   Tue, 25 Jan 2022 15:37:11 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Eliav Farber <farbere@...zon.com>
Cc:     mchehab@...nel.org, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org, ronenk@...zon.com, talel@...zon.com,
        hhhawa@...zon.com, jonnyc@...zon.com, hanochu@...zon.com
Subject: Re: [PATCH 1/4] EDAC: Fix calculation of returned address and next
 offset in edac_align_ptr()

On Thu, Jan 13, 2022 at 10:06:19AM +0000, Eliav Farber wrote:
> Do alignment logic properly and use 'ptr' for calculating the remainder
> of the alignment.
> 
> This became an issue because 'struct edac_mc_layer' has a size that is
> not zero modulo eight, and the next offset that was prepared for the
> private-data was unaligned, causing an alignment exception.

How exactly did this "become an issue"?

I'm asking because I have been hearing about weird bugs with that
pointer alignment contraption and have never managed to reproduce them
myself or hear a proper explanation from people.

And that thing is an abomination, frankly, and I'd like to get rid of it
but maybe some other time...

So, please explain more verbosely, a specific example or how I could
reproduce it, would be even better.

Thx.

-- 
Regards/Gruss,
    Boris.

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