From mboxrd@z Thu Jan  1 00:00:00 1970
From: johan@kernel.org (Johan Hovold)
Date: Thu, 7 Jun 2018 12:27:01 +0200
Subject: [PATCH v5 2/4] kernel hacking: new config NO_AUTO_INLINE to
 disable compiler auto-inline optimizations
In-Reply-To: <314bb2b3-186e-d7b0-d800-f77a42fd80fa@linaro.org>
References: <20180606142600.GN13775@localhost>
 <20180606142622.2338abf6@vmware.local.home>
 <20180607041718.qpqucjzlvcm5h3gn@vireshk-i7>
 <20180607074628.kd3iyxevwj3ypzbr@intel.com>
 <20180607083856.ealw62v3wx43zeqz@vireshk-i7>
 <1303b1abf9f9229a8d3ccbb68a3e413266b360d7.camel@petrovitsch.priv.at>
 <20180607091025.m7dfix3e2xbwx4cs@vireshk-i7>
 <20180607091816.GT13775@localhost>
 <20180607091923.n5q5uzsxuymy3vov@vireshk-i7>
 <314bb2b3-186e-d7b0-d800-f77a42fd80fa@linaro.org>
Message-ID: <20180607102701.GU13775@localhost>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

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