Re: [PATCH v2 1/2] include/uapi/linux/swab.h: move default implementation for swab macros into asm-generic

Ignacio Encinas Rubio
2025-03-19T21:37:53Z

On 19/3/25 22:12, Arnd Bergmann wrote:
> On Wed, Mar 19, 2025, at 22:09, Ignacio Encinas wrote:
>> Move the default byteswap implementation into asm-generic so that it can
>> be included from arch code.
>>
>> This is required by RISC-V in order to have a fallback implementation
>> without duplicating it.
>>
>> Signed-off-by: Ignacio Encinas <ignacio@iencinas.com>
>> ---
>> include/uapi/asm-generic/swab.h | 32 ++++++++++++++++++++++++++++++++
>> include/uapi/linux/swab.h | 33 +--------------------------------
>> 2 files changed, 33 insertions(+), 32 deletions(-)
>>
>
> I think we should just remove these entirely in favor of the
> compiler-povided built-ins.

Got it. I assumed they existed to explicitly avoid relying on
__builtin_bswap as they might not exist. However, I did a quick grep and
found that there are some uses in the wild.

I couldn't find compiler builtins for ___constant_swahb32 nor
___constant_swahw32, so I guess I'll leave them as they are.

Thank you!