On Thu, Mar 01, 2018 at 03:55:16PM +0000, Marc Zyngier wrote:
> We've so far relied on a patching infrastructure that only gave us
> a single alternative, without any way to provide a range of potential
> replacement instructions. For a single feature, this is an all or
> nothing thing.
>
> It would be interesting to have a more flexible grained way of patching
> the kernel though, where we could dynamically tune the code that gets
> injected.
>
> In order to achive this, let's introduce a new form of dynamic patching,
> assiciating a callback to a patching site. This callback gets source and
> target locations of the patching request, as well as the number of
> instructions to be patched.
>
> Dynamic patching is declared with the new ALTERNATIVE_CB and alternative_cb
> directives:
>
> asm volatile(ALTERNATIVE_CB("mov %0, #0\n", callback)
> : "r" (v));
> or
> alternative_cb callback
> mov x0, #0
> alternative_cb_end
>
> where callback is the C function computing the alternative.
>
> Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
