On Mon, Mar 09, 2020 at 11:11:05AM +0900, Masahiro Yamada wrote: > Hi Nathan, > > On Sun, Mar 8, 2020 at 4:34 PM Nathan Chancellor > <natechancellor@xxxxxxxxx> wrote: > > > > Clang's -Wpointer-to-int-cast deviates from GCC in that it warns when > > casting to enums. The kernel does this in certain places, such as device > > tree matches to set the version of the device being used, which allows > > the kernel to avoid using a gigantic union. > > > > https://elixir.bootlin.com/linux/v5.5.8/source/drivers/ata/ahci_brcm.c#L428 > > https://elixir.bootlin.com/linux/v5.5.8/source/drivers/ata/ahci_brcm.c#L402 > > https://elixir.bootlin.com/linux/v5.5.8/source/include/linux/mod_devicetable.h#L264 > > > > To avoid a ton of false positive warnings, disable this particular part > > of the warning, which has been split off into a separate diagnostic so > > that the entire warning does not need to be turned off for clang. > > > > Cc: stable@xxxxxxxxxxxxxxx > > Link: https://github.com/ClangBuiltLinux/linux/issues/887 > > Link: https://github.com/llvm/llvm-project/commit/2a41b31fcdfcb67ab7038fc2ffb606fd50b83a84 > > Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx> > > --- > > Makefile | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/Makefile b/Makefile > > index 86035d866f2c..90e56d5657c9 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -748,6 +748,10 @@ KBUILD_CFLAGS += -Wno-tautological-compare > > # source of a reference will be _MergedGlobals and not on of the whitelisted names. > > # See modpost pattern 2 > > KBUILD_CFLAGS += -mno-global-merge > > +# clang's -Wpointer-to-int-cast warns when casting to enums, which does not match GCC. > > +# Disable that part of the warning because it is very noisy across the kernel and does > > +# not point out any real bugs. > > +KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast) > > else > > > > I'd rather want to fix all the call-sites (97 drivers?) > instead of having -Wno-pointer-to-enum-cast forever. Yes, there are 97 unique warnings across my builds, which are mainly arm, arm64, and x86_64 defconfig/allmodconfig/allyesconfig: https://github.com/ClangBuiltLinux/linux/issues/887#issuecomment-587938406 > If it is tedious to fix them all for now, can we add it > into scripts/Makefile.extrawarn so that this is disabled > by default, but shows up with W=1 builds? Sure, I can send v2 to do that but I think that sending 97 patches just casting the small values (usually less than twenty) to unsigned long then to the enum is rather frivolous. I audited at least ten to fifteen of these call sites when creating the clang patch and they are all basically false positives. I believe Nick discussed this with some other developers off list, maybe he has some other feedback to give. I'll wait to send a v2 until tomorrow in case anyone else has further comments. > (When we fix most of them, we will be able to > make it a real warning.) > > > What do you think? > > Thanks. Cheers, Nathan
