On Tue, Sep 27, 2022 at 09:45:17AM -0700, Nick Desaulniers wrote: > On Tue, Sep 27, 2022 at 8:15 AM Zeng Heng <zengheng4@xxxxxxxxxx> wrote: > > > > Provide implicit enum-conversion warning option > > in general build. When it set enabled, it can > > detect implicit enum type conversion and find > > potential conversion errors like below > > (use "allmodconfig"): > > > > drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn20/display_mode_vba_20.c:3904:46: > > error: implicit conversion from ‘enum <anonymous>’ to ‘enum odm_combine_mode’ [-Werror=enum-conversion] > > 3904 | locals->ODMCombineEnablePerState[i][k] = true; > > | ^ > > > > The '-Wenum-conversion' could be regarded as > > effective check on compile runtime and > > call attention on potential mistakes. > > > > Anothor practical example could be referred to: > > https://lore.kernel.org/all/CADnq5_OE0yZvEYGu82QJHL9wvVcTFZrmeTgX7URgh7FVA=jqYg@xxxxxxxxxxxxxx > > > > "-Wenum-conversion" was firstly introduced from > > GNU gcc-10. > > What about clang? ;) > > > > > Although "-Wenum-conversion" could be enabled > > by "-Wextra" when compiling with 'W=1' option, > > there are many warnings generated by '-Wextra' > > that cause too much noise in a build. > > With clang, I believe that -Wenum-conversion is part of -Wall or > -Wextra; so enabling this explicitly is only necessary for GCC. I > wonder why it's not part of -Wall or -Wextra for GCC? Perhaps worth a > bug report/feature request? With clang, -Wenum-conversion is just default enabled, not even behind -Wall: $ cat test.c enum enum1 { A = 1 }; enum enum2 { B = 2 }; enum enum1 foo(enum enum2 bar) { return bar; } $ clang -fsyntax-only test.c test.c:11:9: warning: implicit conversion from enumeration type 'enum enum2' to different enumeration type 'enum enum1' [-Wenum-conversion] return bar; ~~~~~~ ^~~ 1 warning generated. On the other hand, GCC does have it under -Wextra: $ gcc -fsyntax-only test.c $ gcc -Wextra -fsyntax-only test.c test.c: In function ‘foo’: test.c:6:16: warning: implicit conversion from ‘enum enum2’ to ‘enum enum1’ [-Wenum-conversion] 6 | return bar; | ^~~ But the kernel does not build with -Wextra aside from W=[123], hence this warning has to be explicitly requested for GCC. > > > > Seeing the details from the following link: > > https://gcc.gnu.org/onlinedocs/gcc-11.3.0/gcc/Warning-Options.html > > > > Because there are still some concerned warnings > > exist, the patch marks the option disabled in default > > for avoiding compile failed like using "allmodconfig". But there is no dependency to avoid this getting enabled by allmodconfig (such as 'depends on !COMPILE_TEST') so I don't see the point in the current form; 'default n' does nothing to prevent it. Regardless, I agree with Nick's sentiment below. > > Signed-off-by: Zeng Heng <zengheng4@xxxxxxxxxx> > > --- > > Makefile | 5 +++++ > > lib/Kconfig.debug | 7 +++++++ > > 2 files changed, 12 insertions(+) > > > > diff --git a/Makefile b/Makefile > > index ebd48fc956a3..1790a3624358 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -880,6 +880,11 @@ endif > > KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable) > > KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable) > > > > +# check implicit enum conversion > > +ifdef CONFIG_ENUM_CONVERSION > > +KBUILD_CFLAGS += -Wenum-conversion > > +endif > > Having a kconfig for this is overkill. cc-option with a comment about > the compiler default versions is the way to go. Agreed. If there is some reason -Wenum-conversion cannot be enabled for GCC right now (such as existing warnings, which the commit message appears to alude to), they should be cleaned up first then -Wenum-conversion should just be unconditionally enabled for all compilers that support it via cc-option, not half enabled via Kconfig so that maybe people will clean up the warnings. That is not how enabling warnings works: https://lore.kernel.org/CAHk-=wg-mH-_GYpkhz_psjBWG6ZcjKnPo83fg7YMj_by+-LRTQ@xxxxxxxxxxxxxx/ > > + > > # These result in bogus false positives > > KBUILD_CFLAGS += $(call cc-disable-warning, dangling-pointer) > > > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > index 4f2b81229a2f..a64e06a747d8 100644 > > --- a/lib/Kconfig.debug > > +++ b/lib/Kconfig.debug > > @@ -417,6 +417,13 @@ config FRAME_WARN > > Setting this too low will cause a lot of warnings. > > Setting it to 0 disables the warning. > > > > +config ENUM_CONVERSION > > + bool "Warn for implicit enum conversion" > > + depends on GCC_VERSION >= 100300 > > + default n > > + help > > + Tell gcc to warn at build time for implicit enum conversion. > > + > > config STRIP_ASM_SYMS > > bool "Strip assembler-generated symbols during link" > > default n > > -- > > 2.25.1 > > > > > -- > Thanks, > ~Nick Desaulniers >
