Re: [Xen-devel] [PATCH v5 11/28] xsplice: Implement support for applying/reverting/replacing patches.

[Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>]

On Thu, Apr 07, 2016 at 09:43:38AM -0600, Jan Beulich wrote:
> >>> On 07.04.16 at 05:09, <konrad.wilk@xxxxxxxxxx> wrote:
> >> > +    uint8_t *old_ptr;
> >> > +
> >> > +    BUILD_BUG_ON(PATCH_INSN_SIZE > sizeof(func->undo));
> >> > +    BUILD_BUG_ON(PATCH_INSN_SIZE != (1 + sizeof val));
> >> > +
> >> > +    old_ptr = (uint8_t *)func->old_addr;
> >> 
> >> (Considering this cast, the "old_addr" member should be
> >> unsigned long (or void *), not uint64_t: The latest on ARM32
> >> such would otherwise cause problems.)
> > 
> > I has to be uint8_t to make the single byte modifications. Keep
> > also in mind that this file is only for x86.
> 
> old_addr can't reasonably be uint8_t, so I can only assume you're
> mixing up things here. (And yes, I do realize this is x86 code, but
> my reference to ARM32 was only mean to say that there you'll
> need to do something similar, and casting uint64_t to whatever
> kind of pointer type is not going to work without compiler warning.)

Way back .. when we spoke about the .xsplice.funcs structure
you recommended to make the types be either uintXX specific
or Elf types. I choose Elf types but then we realized that
ARM32 hypervisor would be involved which of course would have
a different size of the structure. So I went with uintXXX
to save a bit of headache (specifically those BUILD_BUG_ON
checks).

I can't see making the old_addr be unsigned long or void *,
which means going back to Elf types. And for ARM32 I will
have to deal with a different structure size. 

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