linux-kernel - Re: [PATCH v6 0/2] lib: checksum: Fix issues with checksum tests

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Message-ID: <Zcmr8C1dTuaPvXqJ@ghost>
Date: Mon, 12 Feb 2024 00:26:08 -0500
From: Charlie Jenkins <charlie@...osinc.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: David Laight <David.Laight@...lab.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v6 0/2] lib: checksum: Fix issues with checksum tests

On Sun, Feb 11, 2024 at 11:18:36AM -0800, Guenter Roeck wrote:
> Hi,
> 
> On 2/7/24 16:22, Charlie Jenkins wrote:
> > The ip_fast_csum and csum_ipv6_magic tests did not have the data
> > types properly casted, and improperly misaligned data.
> > 
> > Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> 
> I sorted out most of the problems with this version, but I still get:
> 
>     # test_csum_ipv6_magic: ASSERTION FAILED at lib/checksum_kunit.c:513
>     Expected ( u64)csum_result == ( u64)expected, but
>         ( u64)csum_result == 16630 (0x40f6)
>         ( u64)expected == 65535 (0xffff)
>     not ok 5 test_csum_ipv6_magic
> 
> on m68k:q800. This is suspicious because there is no 0xffff in
> expected_csum_ipv6_magic[]. With some debugging information:
> 
> ####### num_tests=86 i=84 expect array size=84
> ####### MAX_LEN=512 WORD_ALIGNMENT=4 magic data size=42
> 
> That means the loop
> 
> 	for (int i = 0; i < num_tests; i++) {
> 		...
> 		expected = (__force __sum16)expected_csum_ipv6_magic[i];
> 		...
> 	}
> 
> will access data beyond the end of the expected_csum_ipv6_magic[] array,
> possibly because m68k doesn't pad struct csum_ipv6_magic_data to 44 bytes.

Okay I will check that out.

> 
> In this context, is the comment about proto having to be 0 really true ?
> It seems to me that the calculated checksum must be identical on both
> little and big endian systems. After all, they need to be able to talk
> to each other.

I agree, but I couldn't find a solution other than setting it to zero.
Maybe I am missing something simple...

- Charlie

> 
> Thanks,
> Guenter
>