Am 23.06.2011 16:25, schrieb Alan Stern:
On Thu, 23 Jun 2011, Alexander Holler wrote:
Sorry, I never wanted to talk about the issue itself (I've already said
that), I just wanted to bring in some additional clarity for people
looking at the code.
I think if there is a packed,aligned(4) most people reading that are
able to imaging how the struct looks like, whereas nothing (without
packed) might leave doubts which than requires to read compiler docs or
the generated code, if one searches a problem in that area.
I disagree. If there are no annotations at all (no packed), there
should be no doubts. The compiler will add padding wherever it is
needed for internal alignment and perhaps also at the end of the
structure. Nowhere else.
I agree to disagree but I assume thats ok. ;)
Let me finally add some maybe interesting or informational points for
those who are working or examing the issue and/or who might be involved
in other discussions on the reason for removing the packed:
- I didn't have any problems booting from ehci with kernels compiled
with gcc 4.6 on armv5 (or x86*).
- 2.6.38.4 (and below) compiled with gcc 4.6 booted from ehci (on a
classic beagleboard c4, armv7), whereas everything from 2.6.38.5 upwards
didn't (same compiler, same config). I've discovered that before having
seen that this might be the issue with the packed, therefor I haven't
tested if 2.6.38.5 might work without a packed and have just used gcc
4.5.x for 2.6.38.x. I have tested that a 2,6,39.x compiled with gcc 4.6
and with a removed packed boots from ehci on the beagleboard, so the
patch which removes the packed might be a candidate for the stable tree.
The reason why booting from ehci stopped with 2.6.38.5+ (gcc 4.6) might
be interesting for someone. Looking at the git log I haven't seen
something special and I don't know why anything below 2.6.38.5 worked
with gcc 4.6 and the packed.
- I don't like the idea that every member of every packed struct
(without an aligned) might be handled byte by byte. It might be
necessary but I still don't like it and would prefer the old behaviour
of gcc. I've added this point just to express my personal humble opinion
and I don't want to get involved in a discussion on that topic. ;)
I've just got involved on that topic by accident and never have had a
real reason to do something there (I've done that just for fun).
Therefore I now prefer to disappear, which means there is absolutely no
reason to respond (to me) or to explain anything to me.
Regards and sorry if I wasted someones time,
Alexander
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