Messages in this thread | | | Date | Mon, 11 Dec 2006 00:00:53 +0100 | From | Stefan Richter <> | Subject | alignment and packing of struct types (was Re: [PATCH 2/3] Import fw-ohci driver.) |
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I wrote: > Kristian Høgsberg wrote: >> Stefan Richter wrote: >>> Kristian Høgsberg wrote: >>>> Yup, I've done away with the bitfields and switched to a mix of __le16 >>>> and __le32 struct fields. >>> I suppose the struct should get __attribute__((packed)) then. >> I guess it wouldn't harm, but is it really necessary? Would gcc ever >> insert padding here, all the 32 bit fields a 32 bit aligned, and so are >> the 16 bit fields. > > Is 2-byte alignment of 16bit struct members guaranteed on all platforms? > > A related question: > If I specify a struct which, among else, contains 32bit quantities, then > any variable of this struct type is supposed to be at least 4-byte-aligned. > No if I specifiy this struct as packed, will variables of this type still > be aligned on 4 byte boundaries or will the compiler assume no alignment? > In other words, should it be __attribute__((packed,aligned(4))) then? > I'm speaking about situations where I not only wish to avoid unnecessarily > bad machine code due to unaligned access but where the device requires > 4-byte alignment too.
After sending this, I realized I should have changed the subject. :-) -- Stefan Richter -=====-=-==- ==-- -=-=- http://arcgraph.de/sr/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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