linux-kernel - Re: [PATCH 0/3] Introduce KUNIT_EXPECT_ARREQ and KUNIT_EXPECT

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Date:   Tue, 2 Aug 2022 09:59:59 -0700
From:   Daniel Latypov <dlatypov@...gle.com>
To:     Maíra Canal <mairacanal@...eup.net>
Cc:     Brendan Higgins <brendanhiggins@...gle.com>, davidgow@...gle.com,
        airlied@...ux.ie, daniel@...ll.ch, davem@...emloft.net,
        kuba@...nel.org, jose.exposito89@...il.com, javierm@...hat.com,
        andrealmeid@...eup.net, melissa.srw@...il.com,
        siqueirajordao@...eup.net, Isabella Basso <isabbasso@...eup.net>,
        magalilemes00@...il.com, tales.aparecida@...il.com,
        linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] Introduce KUNIT_EXPECT_ARREQ and KUNIT_EXPECT_ARRNEQ macros

On Tue, Aug 2, 2022 at 9:12 AM Maíra Canal <mairacanal@...eup.net> wrote:
>
> Currently, in order to compare arrays in KUnit, the KUNIT_EXPECT_EQ or
> KUNIT_EXPECT_FALSE macros are used in conjunction with the memcmp function,
> such as:
>   KUNIT_EXPECT_EQ(test, memcmp(foo, bar, size), 0);
>
> Although this usage produces correct results for the test cases, if the
> expectation fails the error message is not very helpful, indicating only the
> return of the memcmp function.
>
> Therefore, create a new set of macros KUNIT_EXPECT_ARREQ and
> KUNIT_EXPECT_ARRNEQ that compare memory blocks until a determined size. In
> case of expectation failure, those macros print the hex dump of the memory
> blocks, making it easier to debug test failures for arrays.

I totally agree with this.

The only reason I hadn't sent an RFC out for this so far is
* we didn't have enough use cases quite yet (now resolved)
* I wasn't sure how we'd want to format the failure message.

For the latter, right now this series produces
dst ==
00000000: 33 0a 60 12 00 a8 00 00 00 00 8e 6b 33 0a 60 12
00000010: 00 00 00 00 00 a8 8e 6b 33 0a 00 00 00 00
result->expected ==
00000000: 31 0a 60 12 00 a8 00 00 00 00 81 6b 33 0a 60 12
00000010: 00 00 00 00 01 a8 8e 6b 33 0a 00 00 00 00

I was thinking something like what KASAN produces would be nice, e.g.
from https://www.kernel.org/doc/html/v5.19/dev-tools/kasan.html#error-reports
(I'll paste the bit here, but my email client doesn't support
monospaced fonts, so it won't look nice on my end)

Memory state around the buggy address:
 ffff8801f44ec200: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
 ffff8801f44ec280: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>ffff8801f44ec300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 03
                                                                ^
I just wasn't quite sure how to do it for a diff, since this only
really works well when showing one bad byte.
If we blindly followed that approach, we get

dst ==
>00000000: 33 0a 60 12 00 a8 00 00 00 00 8e 6b 33 0a 60 12
                                          ^
>00000010: 00 00 00 00 00 a8 8e 6b 33 0a 00 00 00 00
                        ^
result->expected ==
>00000000: 31 0a 60 12 00 a8 00 00 00 00 81 6b 33 0a 60 12
                                          ^
>00000010: 00 00 00 00 01 a8 8e 6b 33 0a 00 00 00 00
                        ^

But perhaps we could instead highlight the bad bytes with something like
dst ==
00000000: 33 0a 60 12 00 a8 00 00 00 00 <8e> 6b 33 0a 60 12
00000010: 00 00 00 00 <00> a8 8e 6b 33 0a 00 00 00 00
result->expected ==
00000000: 31 0a 60 12 00 a8 00 00 00 00 <81> 6b 33 0a 60 12
00000010: 00 00 00 00 <01> a8 8e 6b 33 0a 00 00 00 00

Thoughts, suggestions?