linux-kernel - Re: [PATCH v5 2/4] kernel hacking: new config NO_AUTO_INLINE to disable compiler auto-inline optimizations

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Date:   Thu, 7 Jun 2018 12:27:01 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Alex Elder <elder@...aro.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Johan Hovold <johan@...nel.org>,
        Bernd Petrovitsch <bernd@...rovitsch.priv.at>,
        "Du, Changbin" <changbin.du@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        gregkh@...uxfoundation.org, alex.elder@...aro.org,
        kbuild test robot <lkp@...el.com>,
        linux-arch@...r.kernel.org, michal.lkml@...kovi.net,
        linux-kernel@...r.kernel.org, arnd@...db.de,
        yamada.masahiro@...ionext.com, lgirdwood@...il.com,
        broonie@...nel.org, rdunlap@...radead.org, x86@...nel.org,
        linux@...linux.org.uk, linux-sparse@...r.kernel.org,
        mingo@...hat.com, kbuild-all@...org, akpm@...ux-foundation.org,
        changbin.du@...il.com, tglx@...utronix.de,
        linux-kbuild@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 2/4] kernel hacking: new config NO_AUTO_INLINE to
 disable compiler auto-inline optimizations

On Thu, Jun 07, 2018 at 05:12:51AM -0500, Alex Elder wrote:
> On 06/07/2018 04:19 AM, Viresh Kumar wrote:
> > On 07-06-18, 11:18, Johan Hovold wrote:
> >> If you want to work around the warning and think you can do it in some
> >> non-contrived way, then go for it.
> >>
> >> Clearing the request buffer, checking for termination using strnlen, and
> >> then using memcpy might not be too bad.
> >>
> >> But after all, it is a false positive, so leaving things as they stand
> >> is fine too.
> > 
> > Leave it then :)
> > 
> 
> It's interesting that the warning isn't reported for this in
> fw_mgmt_interface_fw_version_operation().  The difference there is
> that you actually put a zero byte at that last position before
> returning.  I'm mildly impressed if gcc is distinguishing that.

Found a redhat blog post claiming it does check for some cases like
that:

	https://developers.redhat.com/blog/2018/05/24/detecting-string-truncation-with-gcc-8/

> You *are* returning the fw_info->firmware_tag array newly filled
> with a non-null-terminated string in one of the two cases that
> get warnings in "fw-management.c".

No, there's no warning for that one (line 250), and there fw_info is
used as the source, not the destination, so no unterminated string is
returned there either.

> But the other one is only
> updating a buffer in a local/automatic variable.

All three cases, except the one that is explicitly terminated.

> Weird.  I wish there were a non-clumsy way of marking false positives
> like this as A-OK.

The gcc docs mentions an attribute for that but it seems a bit overkill
here.

Thanks,
Johan