linux-kernel - Re: [PATCH v2] lib/string.c: implement a basic bcmp

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Date:   Wed, 13 Mar 2019 20:34:11 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        clang-built-linux@...glegroups.com,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        "# 3.4.x" <stable@...r.kernel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Adhemerval Zanella <adhemerval.zanella@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        James Y Knight <jyknight@...gle.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] lib/string.c: implement a basic bcmp

On 13/03/2019 20.01, Steven Rostedt wrote:
> On Wed, 13 Mar 2019 11:51:09 -0700
> Nick Desaulniers <ndesaulniers@...gle.com> wrote:
> 
>>>
>>> or have a better comment explaining why its the same.  
>>
>> I could add something about "the signedness of the return code not
>> providing any meaning."  What would you like to see in such a comment?
> 
> I think it's the wording that bothers me:
> 
> + * bcmp - Like memcmp but a non-zero return code simply indicates a non-match.
> 
> What about:
> 
>   * bcmp - Like memcmp but non-zero only means a non-match
> 
> Then in the description say that bcmp() callers must not expect
> anything more than zero and non-zero,

Yes, but let's completely avoid mentioning memcmp in the summary.

bcmp - return 0 if and only if the buffers have identical contents
@a: pointer to first buffer
@b: pointer to second buffer
@len: size of buffers

The sign or magnitude of a non-zero return value has no particular
meaning, and architectures may implement their own more efficient
bcmp(). So while this particular implementation is a simple (tail) call
to memcmp, do not rely on anything but whether the return value is zero
or non-zero.

Rasmus