[PATCH] kbuild: add -Werror=implicit-function-declaration

[Simon Glass]

Hi,

On Sun, 10 May 2020 at 20:14, Marek Vasut <marex at denx.de> wrote:
>
> On 5/11/20 3:59 AM, Masahiro Yamada wrote:
> > Hi Simon,
> >
> > On Mon, May 11, 2020 at 5:37 AM Simon Glass <sjg at chromium.org> wrote:
> >>
> >> Hi Masahiro,
> >>
> >> On Sat, 9 May 2020 at 05:00, Masahiro Yamada <masahiroy at kernel.org> wrote:
> >>>
> >>> On Sat, May 9, 2020 at 3:16 AM Tom Rini <trini at konsulko.com> wrote:
> >>>>
> >>>> On Thu, May 07, 2020 at 09:16:40PM -0600, Simon Glass wrote:
> >>>>> Hi Masahiro,
> >>>>>
> >>>>> On Thu, 7 May 2020 at 19:54, Masahiro Yamada <masahiroy at kernel.org> wrote:
> >>>>>>
> >>>>>> On Fri, May 8, 2020 at 10:39 AM Simon Glass <sjg at chromium.org> wrote:
> >>>>>>>
> >>>>>>> Hi Masahiro,
> >>>>>>>
> >>>>>>> On Thu, 7 May 2020 at 06:21, Masahiro Yamada
> >>>>>>> <yamada.masahiro at socionext.com> wrote:
> >>>>>>>>
> >>>>>>>> Add -Werror=implicit-function-declaration as Linux does.
> >>>>>>>>
> >>>>>>>> If you do not check the prototype, it may go wrong run-time.
> >>>>>>>> It is better to break the build, and require to include correct
> >>>>>>>> headers.
> >>>>>>>>
> >>>>>>>> Signed-off-by: Masahiro Yamada <yamada.masahiro at socionext.com>
> >>>>>>>> ---
> >>>>>>>>
> >>>>>>>>  Makefile | 2 +-
> >>>>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>>>>
> >>>>>>> NAK
> >>>>>>>
> >>>>>>> We already get a warning in this situation. This makes it painful for
> >>>>>>> development since things that should be warnings end up being errors.
> >>>>>>> So your build fails when really it should work well enough to do a
> >>>>>>> test run with your new code. I don't think it has any benefit on code
> >>>>>>> quality since we already detect warnings in gitlab, etc.
> >>>>>>>
> >>>>>>> U-Boot is set up so that warnings are reported and are easy to spot if
> >>>>>>> you use 'make -s' (i.e. not buried in the output).
> >>>>>>>
> >>>>>>> Regards,
> >>>>>>> Simon
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>> Linux added this flag in 2007.
> >>>>>>
> >>>>>> The intention seems to break the build earlier
> >>>>>> when a non-existing function is used.
> >>>>>>
> >>>>>> I have not seen compliant about this flag in Linux.
> >>>>>> What does it make different for U-Boot ?
> >>>>>
> >>>>> Well that commit message is quite misleading. The author is presumably
> >>>>> ignoring the warnings that come out in the compile phase. For me they
> >>>>> come up loud and clear. I don't know why it takes half an hour to get
> >>>>> to the link stage. My average incremental build time is under 4
> >>>>> seconds including the link.
> >>>>>
> >>>>> Finally, the warning does not tell you anything about whether the
> >>>>> function doesn't exist. It just tells you you have left out a header
> >>>>> file.
> >>>>>
> >>>>> I know how much of a pain this is, because coreboot does this. It does
> >>>>> it partly because there is so much build output that the warnings are
> >>>>> invisible unless they actually halt the build. Even then you have to
> >>>>> search for what went wrong.
> >>>>
> >>>> I'm not immediately sure of the right answer here.  Part of the problem
> >>>> is that even with 'make -s' U-Boot can be horribly noisy due to device
> >>>> tree warnings.  I assume Yamada-san ran in to a problem and was
> >>>> expecting the build to have failed but instead was chasing down a
> >>>> run-time debug until finding this.
> >>>
> >>>
> >>> I did not run into a problem.
> >>>
> >>> When I was replacing <common.h> with some lighter headers,
> >>> I missed some warnings ( but I noticed them after all).
> >>>
> >>> In Linux, if I miss to include a header, it fails to build.
> >>> In U-Boot, it does not.
> >>>
> >>> Personally, I like to align with Linux policy,
> >>> but if you are not comfortable with this patch,
> >>> please feel free to ignore it.
> >>
> >> I really don't understand the point of warnings if we are just going
> >> to turn them into errors.
> >>
> >> How about adding an option to tell U-Boot to use -Werror, etc.? Then
> >> those that what it can enable it.
> >
> >
> > OK.  We can do it with
> >
> >
> > make KCFLAGS=-Werror
>
> I've had a few of these failures due to implicit fn declaration, so I'd
> be all for adding the error by default. And if things error out and you
> are too lazy to spot the error, use make -k ; make -k and the error will
> be right there at the end.

So are you ignoring the warning? Is it because there are so many
device-tree warnings? Should we figure out how to silence those
things?

>
> So I'm fine with this patch as-is.

Perhaps you can use Masahiro's option above?

Regards,
Simon