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

[Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>]

On Sat, Apr 09, 2016 at 10:36:00PM -0400, Konrad Rzeszutek Wilk wrote:
> 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. 

Oh gosh, that is going to be problem with our headers as
I would be now exposing the 'xsplice_patch_func' structure
in a public header which would depend on Elf_X types.

And we do not expose those. Moving the whole elfstructs.h
to public directory is a bit .. harsh.

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