Re: [PATCH v3 2/2] riscv: introduce asm/swab.h

[Ben Dooks <ben.dooks@codethink.co.uk>]

On 04/04/2025 06:58, Arnd Bergmann wrote:
> On Thu, Apr 3, 2025, at 22:34, Ignacio Encinas wrote:
>> +#define ARCH_SWAB(size) \
>> +static __always_inline unsigned long __arch_swab##size(__u##size value) \
>> +{									\
>> +	unsigned long x = value;					\
>> +									\
>> +	if (riscv_has_extension_likely(RISCV_ISA_EXT_ZBB)) {            \
>> +		asm volatile (".option push\n"				\
>> +			      ".option arch,+zbb\n"			\
>> +			      "rev8 %0, %1\n"				\
>> +			      ".option pop\n"				\
>> +			      : "=r" (x) : "r" (x));			\
>> +		return x >> (BITS_PER_LONG - size);			\
>> +	}                                                               \
>> +	return  ___constant_swab##size(value);				\
>> +}
> 
> I think the fallback should really just use the __builtin_bswap
> helpers instead of the ___constant_swab variants. The output
> would be the same, but you can skip patch 1/2.
> 
> I would also suggest dumbing down the macro a bit so you can
> still find the definition with 'git grep __arch_swab64'. Ideally
> just put the function body into a macro but leave the three
> separate inline function definitions.

I thought we explicitly disabled the builtin from gc... I tried doing
this and just ended up with undefined calls from these sites.,

-- 
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius

https://www.codethink.co.uk/privacy.html