Boaz Harrosh wrote:
...
> I don't understand
>
> if you have a structure like
> struct foo {
> u32 one;
> u32 two;
> };
> vs
> struct foo_packed {
> u32 one;
> u32 two;
> } __packed;
>
> Just adding an __attribute__((packed)) to it clearly does not change
> the layout of the structure. Are you saying the __attribute__((packed))
> is an hint to the compiler that foo_packed might be used unaligned. This
> is just brain-dead, because I can use an unaligned pointer to foo just as
> I can to foo_packed. Otherwise there is no difference what-so-ever between
> the two. I have to see it to believe. It is totally the wrong hint in the
> wrong place taking away valuable meaning of saying "please don't use padding
> holes in this structure"
>
> Sorry for been so slow, I just don't get it.
> Boaz
While I'm no gcc guru, I can confirm that gratuitous use of the packed
attribute is suboptimal; adding "packed" to every ondisk structure made
obdump -d xfs.ko | wc -l explode by about 15,000 lines on ia64.
-Eric
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