RE: [PATCH] hpsa: fix boot on ia64 (atomic_t alignment)

David Laight
2021-03-17T13:19:23Z

From: Martin K. Petersen
> Sent: 17 March 2021 02:26
>
> Arnd,
>
> > Actually that still feels wrong: the annotation of the struct is to
> > pack every member, which causes the access to be done in byte units on
> > architectures that do not have hardware unaligned load/store
> > instructions, at least for things like atomic_read() that does not go
> > through a cmpxchg() or ll/sc cycle.
>
> > This change may fix itanium, but it's still not correct. Other
> > architectures would have already been broken before the recent change,
> > but that's not a reason against fixing them now.
>
> I agree. I understand why there are restrictions on fields consumed by
> the hardware. But for fields internal to the driver the packing doesn't
> make sense to me.

Jeepers -- that global #pragma pack(1) is bollocks.

I think there are a couple of __u64 that are 32bit aligned.
Just marking those field __packed __aligned(4) should have
the desired effect.
Or use a typedef for '__u64 with 32bit alignment'.
(There probably ought to be one in types.h)

Then add compile-time asserts that any non-trivial structures
the hardware accesses are the right size.

David

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