linux-kernel - RE: [PATCH v5 2/2] lib: checksum: Use aligned accesses for ip_fast_csum and csum_ipv6

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Date: Thu, 8 Feb 2024 09:54:39 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Charlie Jenkins' <charlie@...osinc.com>, Guenter Roeck
	<linux@...ck-us.net>
CC: Palmer Dabbelt <palmer@...belt.com>, Andrew Morton
	<akpm@...ux-foundation.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v5 2/2] lib: checksum: Use aligned accesses for
 ip_fast_csum and csum_ipv6_magic tests

From: Charlie Jenkins
> Sent: 08 February 2024 00:23
> 
> On Sun, Feb 04, 2024 at 09:41:56AM -0800, Guenter Roeck wrote:
> > Hi,
> >
> > On Tue, Jan 30, 2024 at 11:10:04AM -0800, Charlie Jenkins wrote:
> > > The test cases for ip_fast_csum and csum_ipv6_magic were using arbitrary
> > > alignment of data to iterate through random inputs. ip_fast_csum should
> > > have the data aligned along (14 + NET_IP_ALIGN) bytes and
> > > csum_ipv6_magic should have data aligned along 32-bit boundaries.
> > >
> > >
..
> >
> > So this works on little endian systems. Unfortunately, I still get
> >
..
> >
> > when running the test on big endian systems such as hppa/parisc or sparc.
> 
> Hmm okay it was easy to get this to work on big endian for
> test_ip_fast_csum but test_csum_ipv6_magic was trickier. I will send out
> a new version with the changes.

Instead of trying to save the expected results why not just
calculate them with a 'really dumb' implementation.
(eg: Add 16bit items and then fold.)

For the generic tests, IIRC:
Your test vectors looked random.
They should probably contain some very specific tests cases.
eg:
- Zero length and all zeros - checksum should be zero (not 0xffff).
- Buffers where the final 'fold' needs the carry added in.

	David

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