Re: [Qemu-devel] [patch] add byteordered types

[Paul Brook <paul@codesourcery.com>]

On Wednesday 27 August 2008, Gerd Hoffmann wrote:
> Gerd Hoffmann wrote:
> > Paul Brook wrote:
> >> On Wednesday 27 August 2008, Gerd Hoffmann wrote:
> >>> +typedef struct { uint16_t le; } le16;
> >>
> >> This won't do what you expect on some targets. In particular older ARM
> >> targets align all structs to a word (4-byte) boundary.
> >
> > Is this a default which can be changed by adding alignment atttributes?
>
> ... like this:
>
> -typedef struct { uint16_t le; } le16;
> +typedef struct { uint16_t le; } le16 __attribute__((__aligned__(2)));
>
> Is the size if the struct padded to 4 bytes too (i.e. do I need packed
> too)?

RTFM:

"When used on a struct, or struct member, the `aligned' attribute
     can only increase the alignment; in order to decrease it, the
     `packed' attribute must be specified as well."

Paul