Re: [PATCH] Introduce compat_u64 and compat_s64 types

[David Woodhouse <dwmw2@infradead.org>]

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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