linux-kernel - Re: [PATCH] x86/crc32: use builtins to improve code generation

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Message-ID: <CAGG=3QX-msHuRffAtNCBoqYo=15Z--5RXbPbJ=Tzkb+C9zNSaw@mail.gmail.com>
Date: Thu, 27 Feb 2025 12:57:37 -0800
From: Bill Wendling <morbo@...gle.com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, 
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, Eric Biggers <ebiggers@...nel.org>, 
	Ard Biesheuvel <ardb@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Justin Stitt <justinstitt@...gle.com>, 
	LKML <linux-kernel@...r.kernel.org>, linux-crypto@...r.kernel.org, 
	clang-built-linux <llvm@...ts.linux.dev>
Subject: Re: [PATCH] x86/crc32: use builtins to improve code generation

On Thu, Feb 27, 2025 at 8:26 AM Dave Hansen <dave.hansen@...el.com> wrote:
> On 2/26/25 22:12, Bill Wendling wrote:
> >  #ifdef CONFIG_X86_64
> > -#define CRC32_INST "crc32q %1, %q0"
> > +#define CRC32_INST __builtin_ia32_crc32di
> >  #else
> > -#define CRC32_INST "crc32l %1, %0"
> > +#define CRC32_INST __builtin_ia32_crc32si
> >  #endif
> >
> >  /*
> > @@ -78,10 +78,10 @@ u32 crc32c_le_arch(u32 crc, const u8 *p, size_t len)
> >
> >         for (num_longs = len / sizeof(unsigned long);
> >              num_longs != 0; num_longs--, p += sizeof(unsigned long))
> > -               asm(CRC32_INST : "+r" (crc) : "rm" (*(unsigned long *)p));
> > +               crc = CRC32_INST(crc,  *(unsigned long *)p);
>
> Could we get rid of the macros, please?
>
> unsigned long crc32_ul(unsigned long crc, unsigned long data)
> {
>         if (IS_DEFINED(CONFIG_X86_64))
>                 return __builtin_ia32_crc32di(crc, data)
>         else
>                 return __builtin_ia32_crc32si(crc, data)
> }
>
> I guess it could also do some check like:
>
>         if (sizeof(int) == sizeof(long))
>
> instead of CONFIG_X86_64, but the CONFIG_X86_64 will make it more
> obvious when someone comes through to rip out 32-bit support some day.

I vastly prefer the first way if made "static __always_inline".

-bw