Messages in this thread | | | Subject | Re: [PATCH] Introduce compat_u64 and compat_s64 types | From | David Woodhouse <> | Date | Fri, 15 Jun 2007 13:47:08 +0100 |
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On Fri, 2007-06-15 at 14:40 +0200, Andi Kleen wrote: > > That is broken on all non-x86 architectures,
> It cannot be broken, it just might be somewhat slower
No, Andi. It's broken.
We're speaking of a 32-bit ioctl compat routine. I would say it's more than 'convention' that the structure used by the compat_ioctl routine actually matches the 'real' structure as it gets laid out on the 32-bit architecture.
The 'real' structure as used by the 32-bit userspace does not have the 'packed' attribute. Thus the u64 member of the structure is aligned to 8 bytes on _all_ relevant 32-bit architectures except for i386.
By adding 'packed' in the compat_ioctl routine, you cause it to expect a structure which does not match what userspace is using, for all non-x86 architectures. That's kind of not very compatible. I call that 'broken'.
-- dwmw2
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