linux-kernel - Re: [PATCH] selftests/nolibc: add 7 tests for memcmp()

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Date:   Thu, 27 Oct 2022 11:09:55 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Willy Tarreau <w@....eu>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/nolibc: add 7 tests for memcmp()

On 26/10/2022 21.52, Willy Tarreau wrote:
> On Wed, Oct 26, 2022 at 11:08:41AM +0200, Rasmus Villemoes wrote:
>> On 26/10/2022 07.39, Willy Tarreau wrote:
>>>
>>> No more false positives nor false negatives anymore. I'm sending you
>>> the patch separately.
>>
>> While you're at it, may I suggest also adding a few test cases where the
>> buffers differ by 128, e.g. 0x0 v 0x80 and 0x40 v 0xc0.
> 
> I initially thought about it but changed my mind for +/- 0xc0 that
> covered the same cases in my opinion. Do you have a particular error
> case in mind that would be caught by this one that the other one does
> not catch ?

Not really, but in a sense the opposite: for the +/- 0xc0 case, both
ways of comparison will give the wrong sign because -192 becomes +64 and
vice versa. For +/- 0x80, one way of doing the comparison will
"accidentally" produce the right answer, and I thought that might also
be a little interesting.

I'm fine for proposing a respin of the patch to improve
> it if it brings some value,

It's your call, you can respin, do an incremental patch, or just ignore
me :)

Rasmus