Messages in this thread | | | Date | Wed, 28 Sep 2022 15:17:36 +0800 | Subject | Re: [PATCH -next] Makefile: add implicit enum-conversion check for compile build | From | Zeng Heng <> |
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On 2022/9/28 1:02, Nathan Chancellor wrote: > 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@huawei.com> 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@mail.gmail.com >>> >>> "-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.
Thanks to your replenish about clang.
>>> 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@huawei.com> >>> --- >>> 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. Got it. > 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@mail.gmail.com/
Have sent the patches to fix the involving warnings.
If all the concerned warnings were repaired, I would send the v2 again.
Thanks all.
>>> + >>> # 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 >>
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