linux-kernel - Re: [PATCH v2 01/14] lib/string: extract generic strlen() into __generic

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Message-ID: <20260114101034.7961852a@pumpkin>
Date: Wed, 14 Jan 2026 10:10:34 +0000
From: David Laight <david.laight.linux@...il.com>
To: Eric Biggers <ebiggers@...nel.org>
Cc: Feng Jiang <jiangfeng@...inos.cn>, pjw@...nel.org, palmer@...belt.com,
 aou@...s.berkeley.edu, alex@...ti.fr, kees@...nel.org, andy@...nel.org,
 akpm@...ux-foundation.org, martin.petersen@...cle.com, ardb@...nel.org,
 ajones@...tanamicro.com, conor.dooley@...rochip.com,
 samuel.holland@...ive.com, linus.walleij@...aro.org, nathan@...nel.org,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 01/14] lib/string: extract generic strlen() into
 __generic_strlen()

On Tue, 13 Jan 2026 16:01:51 -0800
Eric Biggers <ebiggers@...nel.org> wrote:

..
> A similar problem exists with the architecture-optimized CRC and crypto
> functions.  Historically, these subsystems exported both generic and
> architecture-optimized functions.
> 
> We've actually been moving away from that design to simplify things.
> For example, for CRC-32C there's now just the crc32c() function which
> delegates to the "best" CRC-32C implementation, with no direct access to
> the generic implementation of CRC-32C.
> 
> crc_kunit then just tests and benchmarks crc32c().  To check how the
> performance of crc32c() changes when its implementation changes (whether
> the change is the addition of an arch-optimized implementation or a
> change in an existing arch-optimized implementation), the developer just
> needs to run crc_kunit with two kernels, before and after.

For the mul_div tests I arranged that the test code could #include the
source for the generic implementation so it could run that as well as
the version compiled into the main kernel.

This involved wrapping the function in:
#if !defined(function) || defined(test_function)
type function(args)
...
}
#if !defined(function)
EXPORT_SYMBOL(function)
#endif
#endif

So the test code can use:
#define function generic_function
#define test_function
#include "function.c"

to get a private copy of the generic code.

	David