From: Russell King - ARM Linux linux@arm.linux.org.uk Date: Sat, 30 Nov 2013 19:15:53 +0000
so there should be no undesired side effect from this packing.
There is a huge side effect from ever using the packed attribute, in that the compiler can assume absolutely nothing about the alignment of any object or sub-object of the type you apply this attribute to.
Even if it is "obvious" that some members will be aligned, the compiler cannot take advantage of this assumption because this attribute also means that an array of such elements might have arbitrary alignment. So you when you get a pointer to one of these objects, the compiler has to assume the worst possible case.
This means using 4 byte loads to load a 32-bit quantity, always, unconditionally, no matter what.
That's why we should do whatever is necessary to align things properly by hand, and use packed only as the last possible and least desirable resort.
I'm not applying this, please try work to implement this more acceptably first.
Thanks.