Messages in this thread | | | Date | Wed, 14 Dec 2016 12:56:12 -0500 (EST) | Subject | Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of md5_transform | From | David Miller <> |
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From: "Jason A. Donenfeld" <Jason@zx2c4.com> Date: Wed, 14 Dec 2016 13:53:10 +0100
> In all current uses of __packed in the code, I think the impact is > precisely zero, because all structures have members in descending > order of size, with each member being a perfect multiple of the one > below it. The __packed is therefore just there for safety, in case > somebody comes in and screws everything up by sticking a u8 in > between.
Just marking the structure __packed, whether necessary or not, makes the compiler assume that the members are not aligned and causes byte-by-byte accesses to be performed for words.
Never, _ever_, use __packed unless absolutely necessary, it pessimizes the code on cpus that require proper alignment of types.
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