On Mon, 20 Jun 2011, Alan Stern wrote: > On Mon, 20 Jun 2011, Nicolas Pitre wrote: > > > On Mon, 20 Jun 2011, Alan Stern wrote: > > > > > On Sun, 19 Jun 2011, Nicolas Pitre wrote: > > > > > > > > > The question is: does the structure really has to be packed? > > > > > > > > > > What do you mean? The structure really does need to be allocated > > > > > without padding between the fields; is that the same thing? So do a > > > > > bunch of other structures that currently have no annotations at all. > > > > > > > > Yes, that's the same thing. The packed attribute tells the compiler > > > > that you don't want it to insert padding in it as it sees fit. > > > > > > I thought the packed attribute does more than that. For example, on > > > some architectures doesn't it also force the compiler to use > > > byte-oriented instructions for accessing the structure's fields? > > > > Yes, but that's a consequence of not being able to access those fields > > in their naturally aligned position anymore. Hence the addition of the > > align attribute to tell the compiler that we know that the structure is > > still aligned to a certain degree letting the compiler to avoid > > byte-oriented instructions when possible. > > Not exactly. As far as I can tell, the ((packed)) attribute caused the > compiler to change the structure's alignment from its natural value to > 1. That's why the fields weren't in their naturally aligned positions > and why removing ((packed)) fixed the problem. Are we talking past each other? Remember that I was the one asking if the align attribute was needed in the first place. If it is not then by all means please get rid of it! But if it _is_ needed, then the generated code can be much better if the packed attribute is _also_ followed by the align attribute to increase it from 1. Nicolas -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
