netdev - RE: [PATCH net-next v2 6/6] net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum header

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Message-ID: <8452678da3a647249780b60e857bb32a@AcuMS.aculab.com>
Date:   Mon, 8 Mar 2021 14:10:46 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Alex Elder' <elder@...aro.org>,
        "subashab@...eaurora.org" <subashab@...eaurora.org>,
        "stranche@...eaurora.org" <stranche@...eaurora.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>
CC:     "sharathv@...eaurora.org" <sharathv@...eaurora.org>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "evgreen@...omium.org" <evgreen@...omium.org>,
        "cpratapa@...eaurora.org" <cpratapa@...eaurora.org>,
        "elder@...nel.org" <elder@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel test robot" <lkp@...el.com>
Subject: RE: [PATCH net-next v2 6/6] net: qualcomm: rmnet: don't use C
 bit-fields in rmnet checksum header

...
> Sort of related, I have been meaning to eliminate the
> pointless __aligned(1) tags on rmnet structures defined
> in <linux/if_rmnet.h>.  It wouldn't hurt to use __packed,
> though I think they're all 4 or 8 bytes naturally anyway.
> Perhaps marking them __aligned(4) would help identify
> potential unaligned accesses?

Don't use __packed (etc) unless the data might be misaligned.
If the architecture doesn't support misaligned memory
accesses then the compiler has to generate code that
does byte accesses and shifts.

__aligned(4) is mostly useful for structures that have
to have an 8-byte field on a 4-byte boundary.
(As happens in the x86 compat32 code.)

	David

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