[PATCH v5 01/23] arm64: alternatives: Add dynamic patching feature

[Catalin Marinas]

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 at linaro.org>
> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>

Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>