linux-kernel - Re: [PATCH -next] btrfs: lzo: Mask instead of divide to fix 32-bit build

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Message-ID: <20211005232321.GK9286@suse.cz>
Date:   Wed, 6 Oct 2021 01:23:21 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Qu Wenruo <wqu@...e.com>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, noreply@...erman.id.au
Subject: Re: [PATCH -next] btrfs: lzo: Mask instead of divide to fix 32-bit
 build

On Tue, Oct 05, 2021 at 11:34:06AM +0200, Geert Uytterhoeven wrote:
> On 32-bit builds (e.g. m68k):
> 
>     ERROR: modpost: "__umoddi3" [fs/btrfs/btrfs.ko] undefined!
> 
> "cur_in - start" is 64-bit, while sectorsize is u32.
> 
> As sectorsize is always a power of two, the 64-by-32 modulo operation
> can be replaced by a much cheaper bitwise AND with "sectorsize - 1".
> 
> Fixes: 0078783c7089fc83 ("btrfs: rework lzo_compress_pages() to make it subpage compatible")
> Reported-by: noreply@...erman.id.au
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>

Thanks. Folded to the patch as it's still in the devel queue.