[PATCH 4/7] riscv: Implement xchg8/16() using Zabha

[Andrea Parri]

> -#define __arch_xchg_masked(prepend, append, r, p, n)			\
> +#define __arch_xchg_masked(swap_sfx, prepend, append, r, p, n)		\

This actually indicates a problem in the current (aka, no Zabha)
implementation: without your series, xchg16() gets mapped to

  lr.w     a2,(a3)
  and      a1,a2,a5
  or       a1,a1,a4
  sc.w     a1,a1,(a3)
  bnez     a1,43c <.L0^B1>

which is clearly wrong... (other "fully-ordered LR/SC sequences"
instead follow the mapping

  lr.w     a2,(a3)
  and      a1,a2,a5
  or       a1,a1,a4
  sc.w.rl  a1,a1,(a3)
  bnez     a1,43c <.L0^B1>
  fence    rw,rw  )

A similar consideration for xchg8().

  Andrea