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

[Ben Dooks]

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.,

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Ben Dooks				http://www.codethink.co.uk/
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