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Date: Sun, 10 Dec 2006 23:59:06 +0100 From: Stefan Richter <stefanr@...6.in-berlin.de> To: Kristian Høgsberg <krh@...hat.com> CC: Jeff Garzik <jeff@...zik.org>, linux-kernel@...r.kernel.org Subject: Re: [PATCH 2/3] Import fw-ohci driver. 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. -- 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@...r.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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