Re: [PATCH v2 01/14] lib/string: extract generic strlen() into __generic_strlen()

From: David Laight <david.laight.linux@gmail.com>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Feng Jiang <jiangfeng@kylinos.cn>,
	pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu,
	alex@ghiti.fr, kees@kernel.org, andy@kernel.org,
	akpm@linux-foundation.org, martin.petersen@oracle.com,
	ardb@kernel.org, ajones@ventanamicro.com,
	conor.dooley@microchip.com, samuel.holland@sifive.com,
	linus.walleij@linaro.org, nathan@kernel.org,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-hardening@vger.kernel.org
Subject: Re: [PATCH v2 01/14] lib/string: extract generic strlen() into __generic_strlen()
Date: Wed, 14 Jan 2026 10:10:34 +0000	[thread overview]
Message-ID: <20260114101034.7961852a@pumpkin> (raw)
In-Reply-To: <20260114000151.GB2178@quark>

On Tue, 13 Jan 2026 16:01:51 -0800
Eric Biggers <ebiggers@kernel.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