linux-kernel - Re: drivers/soc/litex/litex_soc_ctrl.c:143:34: warning: unused variable 'litex_soc_ctrl_of

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Date:   Tue, 12 Jan 2021 06:14:52 +0900
From:   Stafford Horne <shorne@...il.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     kernel test robot <lkp@...el.com>,
        Pawel Czarnecki <pczarnecki@...ernships.antmicro.com>,
        kbuild-all@...ts.01.org, clang-built-linux@...glegroups.com,
        linux-kernel@...r.kernel.org,
        Mateusz Holenko <mholenko@...micro.com>
Subject: Re: drivers/soc/litex/litex_soc_ctrl.c:143:34: warning: unused
 variable 'litex_soc_ctrl_of_match'

On Mon, Jan 11, 2021 at 09:43:34AM -0700, Nathan Chancellor wrote:
> On Mon, Jan 11, 2021 at 09:30:55PM +0900, Stafford Horne wrote:
> > On Thu, Jan 07, 2021 at 04:04:47AM +0800, kernel test robot wrote:
> > > Hi Pawel,
> > > 
> > > FYI, the error/warning still remains.
> > > 
> > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > > head:   e71ba9452f0b5b2e8dc8aa5445198cd9214a6a62
> > > commit: 22447a99c97e353bde8f90c2353873f27681d57c drivers/soc/litex: add LiteX SoC Controller driver
> > > date:   8 weeks ago
> > > config: x86_64-randconfig-a001-20210107 (attached as .config)
> > > compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project 5c951623bc8965fa1e89660f2f5f4a2944e4981a)
> > > reproduce (this is a W=1 build):
> > >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > >         chmod +x ~/bin/make.cross
> > >         # install x86_64 cross compiling tool for clang build
> > >         # apt-get install binutils-x86-64-linux-gnu
> > >         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=22447a99c97e353bde8f90c2353873f27681d57c
> > >         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> > >         git fetch --no-tags linus master
> > >         git checkout 22447a99c97e353bde8f90c2353873f27681d57c
> > >         # save the attached .config to linux build tree
> > >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64 
> > > 
> > > If you fix the issue, kindly add following tag as appropriate
> > > Reported-by: kernel test robot <lkp@...el.com>
> > > 
> > > All warnings (new ones prefixed by >>):
> > > 
> > > >> drivers/soc/litex/litex_soc_ctrl.c:143:34: warning: unused variable 'litex_soc_ctrl_of_match' [-Wunused-const-variable]
> > >    static const struct of_device_id litex_soc_ctrl_of_match[] = {
> > >                                     ^
> > >    1 warning generated.
> > > 
> > > 
> > > vim +/litex_soc_ctrl_of_match +143 drivers/soc/litex/litex_soc_ctrl.c
> > > 
> > >    142	
> > >  > 143	static const struct of_device_id litex_soc_ctrl_of_match[] = {
> > >    144		{.compatible = "litex,soc-controller"},
> > >    145		{},
> > >    146	};
> > >    147	
> > > 
> > 
> > I don't use clang but GCC, and I cannot reproduce this warning.
> > 
> > $ make drivers/soc/litex/litex_soc_ctrl.o 
> >   CALL    scripts/checksyscalls.sh
> >   CALL    scripts/atomic/check-atomics.sh
> >   DESCEND  objtool
> >   CC      drivers/soc/litex/litex_soc_ctrl.o
> > 
> > Also, I can see litex_soc_ctrl_of_match is used.  I am not sure what is going on
> > here.
> > 
> > -Stafford
> > 
> 
> You need W=1
> 
> $ make -skj"$(nproc)" W=1 olddefconfig drivers/soc/litex/litex_soc_ctrl.o
> drivers/soc/litex/litex_soc_ctrl.c:143:34: warning: ‘litex_soc_ctrl_of_match’ defined but not used [-Wunused-const-variable=]
>   143 | static const struct of_device_id litex_soc_ctrl_of_match[] = {
>       |                                  ^~~~~~~~~~~~~~~~~~~~~~~
> 
> $ rg "CONFIG_OF|CONFIG_LITEX_SOC_CONTROLLER" .config
> 1124:# CONFIG_OF is not set
> 4673:CONFIG_LITEX_SOC_CONTROLLER=y
> 
> This variable is used in two places in that file, in the
> MODULE_DEVICE_TABLE macro and the of_match_ptr macro. When CONFIG_OF is
> disabled, of_match_ptr evaluates to NULL. When the file is built into
> the kernel image, MODULE_DEVICE_TABLE evaluates to nothing, leaving this
> variable defined but unused in the final preprocessed source.
> 
> Hope that helps!

That helps, I noticed it was only used in those macros so that was fishy.  I
forgot to add W=1.

We will need to surround the definition in:

#if defined(CONFIG_OF)
#endif /* CONFIG_OF */