Re: [GIT PULL] Add two-byte cmpxchg emulation function for v7.4

[Jan Engelhardt]

On Friday 2026-10-23 18:12, Paul E. McKenney wrote:
>> >
>> >Add emulation of two-byte cmpxchg()
>> >
>> >These commits add a cmpxchg_emu_u16() function that emulates two-byte
>> >cmpxchg() in terms of four-byte cmpxchg() [...] 
>> >namely sh, arc, csky, and xtensa.
>> >
>> >There is reason to believe that these systems will soon no longer be
>> >supported by Linux.
>> 
>> riscv64 also only has two exchange operations 
>> (lr.w.aqrl/lr.d.aqrl/sc.w.rl/sc.d.rl). 
>> (atomic_compare_exchange_strong with uint8/16_t, in userspace, gets 
>> replaced by the compiler to a lot more instructions thanks to 
>> implied -finline-atomics.)
>> 
>> Are you saying riscv64 is going to go unsupported too? ;-)
>
>Given that the compiler can make it work in userspace, then the riscv64
>architecture-specific code should be able to make it work in the Linux
>kernel.  At which point there is absolutely no reason that Linux-kernel
>support for riscv64 should be dropped.
>
>Or am I missing something here?

I can get gcc-17.0.0-20261102 with no further command line options
to turn `atomic_compare_exchange_strong`+uint16 into some object code
that does not contain a call to libatomic, for sh2, sh3, sh4. Haven't 
tried xtensa or the others.
Thus, is the patch really needed?