linux-kernel - Re: arch/arm64/kernel/topology.c:367:22: sparse: sparse: dereference of noderef expression

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Message-ID: <20201218104410.GB5258@gaia>
Date:   Fri, 18 Dec 2020 10:44:10 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     kernel test robot <lkp@...el.com>
Cc:     Ionela Voinescu <ionela.voinescu@....com>, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>
Subject: Re: arch/arm64/kernel/topology.c:367:22: sparse: sparse: dereference
 of noderef expression

On Fri, Dec 18, 2020 at 05:00:16AM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   74f602dc96dd854c7b2034947798c1e2a6b84066
> commit: 68c5debcc06d6d24f15dbf978780fc5efc147d5e arm64: implement CPPC FFH support using AMUs
> date:   5 weeks ago
> config: arm64-randconfig-s032-20201217 (attached as .config)
> compiler: aarch64-linux-gcc (GCC) 9.3.0
> reproduce:
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # apt-get install sparse
>         # sparse version: v0.6.3-184-g1b896707-dirty
>         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=68c5debcc06d6d24f15dbf978780fc5efc147d5e
>         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>         git fetch --no-tags linus master
>         git checkout 68c5debcc06d6d24f15dbf978780fc5efc147d5e
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' ARCH=arm64 
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@...el.com>
> 
> 
> "sparse warnings: (new ones prefixed by >>)"
> >> arch/arm64/kernel/topology.c:367:22: sparse: sparse: dereference of noderef expression
> 
> vim +367 arch/arm64/kernel/topology.c
> 
>    362	
>    363	int cpc_read_ffh(int cpu, struct cpc_reg *reg, u64 *val)
>    364	{
>    365		int ret = -EOPNOTSUPP;
>    366	
>  > 367		switch ((u64)reg->address) {

That's not a dereference but I guess sparse complains of dropping the
__iomem. We could change the cast to (__force u64) to silence sparse.

Thanks for the report.

-- 
Catalin