Re: [Xen-devel] memop struct packing, 32/64 bits

[Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>]

> > luck? Am I missing something?
> 
> Where older structs were not 32/64-bit invariant, compat shims were
> implemented. See common/compat/memory.c, for example. Well worth avoiding
> that!

So for the "Fun" of it I tried to see if the 'struct
xen_processor_performance' has some 32/64-bit issues and was surprised
to find they do. What I am more surprised to find is that nobody seems
to have had any troubles with this as it seems to have been there since
it was initially implemented. The major issue would have been with the
'shared_type', 'domain_info' and the pointer to the 'states' being at
different offsets (So when running a 32-bit dom0 with a 64-bit
hypervisor).

The attached little C program has the identified issues and the
// FIX is my attempt at making the structs of the same size on 32 and 64
bit builds. Right now when built as 32-bit the struct is 96 bytes, while on
64-bit it is 104.

Was wondering what is the right fix? The thoughts I had was to either
leave them as be and the domain would have to figure out whether the hypervisor
is 32-bit or 64-bit and provide the _right_ structure.

Or perhaps fix it and provide a "version" hypercall, but that would not
be backwards compatible.

Attachment: psd.c
Description: Text Data

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