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

[Tom Rini]

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.  It's really easy to build with
-Werror set via buildman, but a lot of people don't expect to have to
use buildman (as it's not required, just a good idea), see for example
the thread about building non-functional sunxi binaries.  If they used
buildman the non-zero exit code would have saved them the debug time.

All that said, I can imagine that doing something like the include
cleanup series that you do would be even harder with this on.  But on
the 3rd or 4th hand, adding -k to make gets those builds going along
anyhow.

Personally, when I see those warnings I fix them up before tossing at
the hardware, but I know that's not everyones workflow.

-- 
Tom
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 659 bytes
Desc: not available
URL: <https://lists.denx.de/pipermail/u-boot/attachments/20200508/69d73c42/attachment.sig>