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SubjectRe: drivers/pinctrl/bcm/pinctrl-bcm2835.c:412:14: warning: variable 'group' is used uninitialized whenever 'for' loop exits because its condition is false
On Tue, Dec 14, 2021 at 10:44:28PM +0800, kernel test robot wrote:
> Hi Jason,
>
> FYI, the error/warning still remains.
>
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head: 5472f14a37421d1bca3dddf33cabd3bd6dbefbbc
> commit: 29d45a642d4ea8de7e89b57f856046df7c3b219f pinctrl: bcm2835: Replace BUG with BUG_ON
> date: 5 months ago
> config: mips-randconfig-c004-20211214 (https://download.01.org/0day-ci/archive/20211214/202112142208.QW0tVv0m-lkp@intel.com/config)
> compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project b6a2ddb6c8ac29412b1361810972e15221fa021c)
> 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 mips cross compiling tool for clang build
> # apt-get install binutils-mips-linux-gnu
> # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=29d45a642d4ea8de7e89b57f856046df7c3b219f
> git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> git fetch --no-tags linus master
> git checkout 29d45a642d4ea8de7e89b57f856046df7c3b219f
> # save the config file to linux build tree
> mkdir build_dir
> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=mips SHELL=/bin/bash drivers/pinctrl/bcm/
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
>
> All warnings (new ones prefixed by >>):
>
> >> drivers/pinctrl/bcm/pinctrl-bcm2835.c:412:14: warning: variable 'group' is used uninitialized whenever 'for' loop exits because its condition is false [-Wsometimes-uninitialized]
> for (i = 0; i < BCM2835_NUM_IRQS; i++) {
> ^~~~~~~~~~~~~~~~~~~~
> drivers/pinctrl/bcm/pinctrl-bcm2835.c:423:10: note: uninitialized use occurs here
> switch (group) {
> ^~~~~
> drivers/pinctrl/bcm/pinctrl-bcm2835.c:412:14: note: remove the condition if it is always true
> for (i = 0; i < BCM2835_NUM_IRQS; i++) {
> ^~~~~~~~~~~~~~~~~~~~
> drivers/pinctrl/bcm/pinctrl-bcm2835.c:409:11: note: initialize the variable 'group' to silence this warning
> int group;
> ^
> = 0
> 1 warning generated.

It seems like MIP's __BUG_ON() makes it harder for clang to figure out
that 'i == BCM2835_NUM_IRQS' will make the kernel panic, which is the
only way that the loop exits because the condition is false.

I am not really sure of a way to fix this other than just reverting that
change or changing the BUG_ON() to WARN_ON().

Cheers,
Nathan

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