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From: "D. Jeff Dionne" <djeffdionne@gmail.com>
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Subject: Re: Problems with csum_partial with misaligned buffers on sh4 platform
Date: Sun, 11 Feb 2024 12:41:16 +0900
Message-Id: <8C704EE6-7B5E-4569-B9C3-84B2CBADA102@gmail.com>
References: <0a0fbbd8-17dd-4f4c-9513-f3ac9749890b@roeck-us.net>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
 Yoshinori Sato <ysato@users.sourceforge.jp>, Rich Felker <dalias@libc.org>,
 linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org
In-Reply-To: <0a0fbbd8-17dd-4f4c-9513-f3ac9749890b@roeck-us.net>
To: Guenter Roeck <linux@roeck-us.net>

I remember there being problems with alignment on SH targets in the network s=
tack.  IIRC, wireguard triggered it in actual use, seems to me it had to do w=
ith skb alignment.

Rich Felker may remember more, but I don=E2=80=99t think we implemented a (c=
omplete) solution.

Cheers,
J.

> On 11 Feb 2024, at 07:03, Guenter Roeck <linux@roeck-us.net> wrote:
>=20
> =EF=BB=BFHi Adrian,
>=20
>> On 2/10/24 12:12, John Paul Adrian Glaubitz wrote:
>> Hi Guenter,
>>> On Sat, 2024-02-10 at 07:12 -0800, Guenter Roeck wrote:
>>> when running checksum unit tests on sh4 qemu emulations, I get the follo=
wing
>>> errors.
>>>=20
>>>     KTAP version 1
>>>     # Subtest: checksum
>>>     # module: checksum_kunit
>>>     1..5
>>>     # test_csum_fixed_random_inputs: ASSERTION FAILED at lib/checksum_ku=
nit.c:500
>>>     Expected ( u64)result =3D=3D ( u64)expec, but
>>>         ( u64)result =3D=3D 53378 (0xd082)
>>>         ( u64)expec =3D=3D 33488 (0x82d0)
>>>     not ok 1 test_csum_fixed_random_inputs
>>>     # test_csum_all_carry_inputs: ASSERTION FAILED at lib/checksum_kunit=
c:525
>>>     Expected ( u64)result =3D=3D ( u64)expec, but
>>>         ( u64)result =3D=3D 65281 (0xff01)
>>>         ( u64)expec =3D=3D 65280 (0xff00)
>>>     not ok 2 test_csum_all_carry_inputs
>>>     # test_csum_no_carry_inputs: ASSERTION FAILED at lib/checksum_kunit.=
c:573
>>>     Expected ( u64)result =3D=3D ( u64)expec, but
>>>         ( u64)result =3D=3D 65535 (0xffff)
>>>         ( u64)expec =3D=3D 65534 (0xfffe)
>>>     not ok 3 test_csum_no_carry_inputs
>>>     ok 4 test_ip_fast_csum
>>>     ok 5 test_csum_ipv6_magic
>>> # checksum: pass:2 fail:3 skip:0 total:5
>>>=20
>>> The above is with from a little endian system. On a big endian system,
>>> the test result is as follows.
>>>=20
>>>     KTAP version 1
>>>     # Subtest: checksum
>>>     # module: checksum_kunit
>>>     1..5
>>>     # test_csum_fixed_random_inputs: ASSERTION FAILED at lib/checksum_ku=
nit.c:500
>>>     Expected ( u64)result =3D=3D ( u64)expec, but
>>>         ( u64)result =3D=3D 33488 (0x82d0)
>>>         ( u64)expec =3D=3D 53378 (0xd082)
>>>     not ok 1 test_csum_fixed_random_inputs
>>>     # test_csum_all_carry_inputs: ASSERTION FAILED at lib/checksum_kunit=
c:525
>>>     Expected ( u64)result =3D=3D ( u64)expec, but
>>>         ( u64)result =3D=3D 65281 (0xff01)
>>>         ( u64)expec =3D=3D 255 (0xff)
>>>     not ok 2 test_csum_all_carry_inputs
>>>     # test_csum_no_carry_inputs: ASSERTION FAILED at lib/checksum_kunit.=
c:565
>>>     Expected ( u64)result =3D=3D ( u64)expec, but
>>>         ( u64)result =3D=3D 1020 (0x3fc)
>>>         ( u64)expec =3D=3D 0 (0x0)
>>>     not ok 3 test_csum_no_carry_inputs
>>>     # test_ip_fast_csum: ASSERTION FAILED at lib/checksum_kunit.c:589
>>>     Expected ( u64)expected =3D=3D ( u64)csum_result, but
>>>         ( u64)expected =3D=3D 55939 (0xda83)
>>>         ( u64)csum_result =3D=3D 33754 (0x83da)
>>>     not ok 4 test_ip_fast_csum
>>>     # test_csum_ipv6_magic: ASSERTION FAILED at lib/checksum_kunit.c:617=

>>>     Expected ( u64)expected_csum_ipv6_magic[i] =3D=3D ( u64)csum_ipv6_ma=
gic(saddr, daddr, len, proto, csum), but
>>>         ( u64)expected_csum_ipv6_magic[i] =3D=3D 6356 (0x18d4)
>>>         ( u64)csum_ipv6_magic(saddr, daddr, len, proto, csum) =3D=3D 435=
86 (0xaa42)
>>>     not ok 5 test_csum_ipv6_magic
>>> # checksum: pass:0 fail:5 skip:0 total:5
>>>=20
>>> Note that test_ip_fast_csum and test_csum_ipv6_magic fail on all big end=
ian
>>> systems due to a bug in the test code, unrelated to this problem.
>>>=20
>>> Analysis shows that the errors are seen only if the buffer is misaligned=
.
>>> Looking into arch/sh/lib/checksum.S, I found commit cadc4e1a2b4d2 ("sh:
>>> Handle calling csum_partial with misaligned data") which seemed to be
>>> related. Reverting that commit fixes the problem.
>>> This suggests that something may be wrong with that commit. Alternativel=
y,
>>> of course, it may be possible that something is wrong with the qemu
>>> emulation, but that seems unlikely.
>> I have not run these tests before. Can you tell me how these are run,
>> so I can verify these reproduce on real hardware?
>=20
> Enabling CONFIG_KUNIT and CONFIG_CHECKSUM_KUNIT on top of a working
> configuration should do the trick. Both can be built as module,
> so presumably one can build and load them separately. I have not tried
> that, though - I always build them into the kernel and boot the resulting
> image.
>=20
> Hope this helps,
> Guenter
>=20
>=20