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

Johan Hovold
2018-06-07T10:27:18Z

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