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

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Message-Id: <20211005093406.1241222-1-geert@linux-m68k.org>
Date:   Tue,  5 Oct 2021 11:34:06 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Qu Wenruo <wqu@...e.com>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>
Cc:     linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        noreply@...erman.id.au
Subject: [PATCH -next] btrfs: lzo: Mask instead of divide to fix 32-bit build

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>
---
Compile-tested only.
---
 fs/btrfs/lzo.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/lzo.c b/fs/btrfs/lzo.c
index 47003cec4046f13e..d08f9eba49dab3cd 100644
--- a/fs/btrfs/lzo.c
+++ b/fs/btrfs/lzo.c
@@ -211,7 +211,7 @@ int lzo_compress_pages(struct list_head *ws, struct address_space *mapping,
 	 */
 	cur_out += LZO_LEN;
 	while (cur_in < start + len) {
-		u32 sector_off = (cur_in - start) % sectorsize;
+		u32 sector_off = (cur_in - start) & (sectorsize - 1);
 		u32 in_len;
 		size_t out_len;
 
-- 
2.25.1