| Message ID | 20190907025236.31393-1-yamada.masahiro@socionext.com |
|---|---|
| State | Accepted |
| Commit | 6863f5643dd717376c2fdc85a47a00f9d738a834 |
| Headers | show |
| Series | [v2] kbuild: allow Clang to find unused static inline functions for W=1 build | expand |
On Sat, Sep 7, 2019 at 11:53 AM Masahiro Yamada <yamada.masahiro@socionext.com> wrote: > > GCC and Clang have different policy for -Wunused-function; GCC does not > warn unused static inline functions at all whereas Clang does if they > are defined in source files instead of included headers although it has > been suppressed since commit abb2ea7dfd82 ("compiler, clang: suppress > warning for unused static inline functions"). > > We often miss to delete unused functions where 'static inline' is used > in *.c files since there is no tool to detect them. Unused code remains > until somebody notices. For example, commit 075ddd75680f ("regulator: > core: remove unused rdev_get_supply()"). > > Let's remove __maybe_unused from the inline macro to allow Clang to > start finding unused static inline functions. For now, we do this only > for W=1 build since it is not a good idea to sprinkle warnings for the > normal build (e.g. 35 warnings for arch/x86/configs/x86_64_defconfig). > > My initial attempt was to add -Wno-unused-function for no W= build > (https://lore.kernel.org/patchwork/patch/1120594/) > > Nathan Chancellor pointed out that would weaken Clang's checks since > we would no longer get -Wunused-function without W=1. It is true GCC > would catch unused static non-inline functions, but it would weaken > Clang as a standalone compiler, at least. > > Hence, here is a counter implementation. The current problem is, W=... > only controls compiler flags, which are globally effective. There is > no way to address only 'static inline' functions. > > This commit defines KBUILD_EXTRA_WARN[123] corresponding to W=[123]. > When KBUILD_EXTRA_WARN1 is defined, __maybe_unused is omitted from > the 'inline' macro. > > The new macro __inline_maybe_unused makes the code a bit uglier, so I > hope we can remove it entirely after fixing most of the warnings. > > If you contribute to code clean-up, please run "make CC=clang W=1" > and check -Wunused-function warnings. You will find lots of unused > functions. > > Some of them are false-positives because the call-sites are disabled > by #ifdef. I do not like to abuse the inline keyword for suppressing > unused-function warnings because it is intended to be a hint for the > compiler optimization. I prefer #ifdef around the definition, or > __maybe_unused if #ifdef would make the code too ugly. > > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> > Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> > Tested-by: Nathan Chancellor <natechancellor@gmail.com> > --- Applied to linux-kbuild. > > Changes in v2: > - Rebase on top of https://patchwork.kernel.org/patch/11124933/ > > include/linux/compiler_types.h | 20 ++++++++++++++------ > scripts/Makefile.extrawarn | 6 ++++++ > 2 files changed, 20 insertions(+), 6 deletions(-) > > diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h > index 599c27b56c29..b056a40116da 100644 > --- a/include/linux/compiler_types.h > +++ b/include/linux/compiler_types.h > @@ -130,10 +130,6 @@ struct ftrace_likely_data { > > /* > * Force always-inline if the user requests it so via the .config. > - * GCC does not warn about unused static inline functions for > - * -Wunused-function. This turns out to avoid the need for complex #ifdef > - * directives. Suppress the warning in clang as well by using "unused" > - * function attribute, which is redundant but not harmful for gcc. > * Prefer gnu_inline, so that extern inline functions do not emit an > * externally visible function. This makes extern inline behave as per gnu89 > * semantics rather than c99. This prevents multiple symbol definition errors > @@ -144,15 +140,27 @@ struct ftrace_likely_data { > */ > #if !defined(CONFIG_OPTIMIZE_INLINING) > #define inline inline __attribute__((__always_inline__)) __gnu_inline \ > - __maybe_unused notrace > + __inline_maybe_unused notrace > #else > #define inline inline __gnu_inline \ > - __maybe_unused notrace > + __inline_maybe_unused notrace > #endif > > #define __inline__ inline > #define __inline inline > > +/* > + * GCC does not warn about unused static inline functions for -Wunused-function. > + * Suppress the warning in clang as well by using __maybe_unused, but enable it > + * for W=1 build. This will allow clang to find unused functions. Remove the > + * __inline_maybe_unused entirely after fixing most of -Wunused-function warnings. > + */ > +#ifdef KBUILD_EXTRA_WARN1 > +#define __inline_maybe_unused > +#else > +#define __inline_maybe_unused __maybe_unused > +#endif > + > /* > * Rather then using noinline to prevent stack consumption, use > * noinline_for_stack instead. For documentation reasons. > diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn > index 53eb7e0c6a5a..ecddf83ac142 100644 > --- a/scripts/Makefile.extrawarn > +++ b/scripts/Makefile.extrawarn > @@ -36,6 +36,8 @@ KBUILD_CFLAGS += $(call cc-option, -Wstringop-truncation) > KBUILD_CFLAGS += -Wno-missing-field-initializers > KBUILD_CFLAGS += -Wno-sign-compare > > +KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1 > + > else > > # Some diagnostics enabled by default are noisy. > @@ -65,6 +67,8 @@ KBUILD_CFLAGS += -Wsign-compare > KBUILD_CFLAGS += $(call cc-option, -Wmaybe-uninitialized) > KBUILD_CFLAGS += $(call cc-option, -Wunused-macros) > > +KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN2 > + > endif > > # > @@ -82,4 +86,6 @@ KBUILD_CFLAGS += -Wredundant-decls > KBUILD_CFLAGS += -Wswitch-default > KBUILD_CFLAGS += $(call cc-option, -Wpacked-bitfield-compat) > > +KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN3 > + > endif > -- > 2.17.1 > -- Best Regards Masahiro Yamada
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 599c27b56c29..b056a40116da 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -130,10 +130,6 @@ struct ftrace_likely_data { /* * Force always-inline if the user requests it so via the .config. - * GCC does not warn about unused static inline functions for - * -Wunused-function. This turns out to avoid the need for complex #ifdef - * directives. Suppress the warning in clang as well by using "unused" - * function attribute, which is redundant but not harmful for gcc. * Prefer gnu_inline, so that extern inline functions do not emit an * externally visible function. This makes extern inline behave as per gnu89 * semantics rather than c99. This prevents multiple symbol definition errors @@ -144,15 +140,27 @@ struct ftrace_likely_data { */ #if !defined(CONFIG_OPTIMIZE_INLINING) #define inline inline __attribute__((__always_inline__)) __gnu_inline \ - __maybe_unused notrace + __inline_maybe_unused notrace #else #define inline inline __gnu_inline \ - __maybe_unused notrace + __inline_maybe_unused notrace #endif #define __inline__ inline #define __inline inline +/* + * GCC does not warn about unused static inline functions for -Wunused-function. + * Suppress the warning in clang as well by using __maybe_unused, but enable it + * for W=1 build. This will allow clang to find unused functions. Remove the + * __inline_maybe_unused entirely after fixing most of -Wunused-function warnings. + */ +#ifdef KBUILD_EXTRA_WARN1 +#define __inline_maybe_unused +#else +#define __inline_maybe_unused __maybe_unused +#endif + /* * Rather then using noinline to prevent stack consumption, use * noinline_for_stack instead. For documentation reasons. diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn index 53eb7e0c6a5a..ecddf83ac142 100644 --- a/scripts/Makefile.extrawarn +++ b/scripts/Makefile.extrawarn @@ -36,6 +36,8 @@ KBUILD_CFLAGS += $(call cc-option, -Wstringop-truncation) KBUILD_CFLAGS += -Wno-missing-field-initializers KBUILD_CFLAGS += -Wno-sign-compare +KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1 + else # Some diagnostics enabled by default are noisy. @@ -65,6 +67,8 @@ KBUILD_CFLAGS += -Wsign-compare KBUILD_CFLAGS += $(call cc-option, -Wmaybe-uninitialized) KBUILD_CFLAGS += $(call cc-option, -Wunused-macros) +KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN2 + endif # @@ -82,4 +86,6 @@ KBUILD_CFLAGS += -Wredundant-decls KBUILD_CFLAGS += -Wswitch-default KBUILD_CFLAGS += $(call cc-option, -Wpacked-bitfield-compat) +KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN3 + endif
GCC and Clang have different policy for -Wunused-function; GCC does not warn unused static inline functions at all whereas Clang does if they are defined in source files instead of included headers although it has been suppressed since commit abb2ea7dfd82 ("compiler, clang: suppress warning for unused static inline functions"). We often miss to delete unused functions where 'static inline' is used in *.c files since there is no tool to detect them. Unused code remains until somebody notices. For example, commit 075ddd75680f ("regulator: core: remove unused rdev_get_supply()"). Let's remove __maybe_unused from the inline macro to allow Clang to start finding unused static inline functions. For now, we do this only for W=1 build since it is not a good idea to sprinkle warnings for the normal build (e.g. 35 warnings for arch/x86/configs/x86_64_defconfig). My initial attempt was to add -Wno-unused-function for no W= build (https://lore.kernel.org/patchwork/patch/1120594/) Nathan Chancellor pointed out that would weaken Clang's checks since we would no longer get -Wunused-function without W=1. It is true GCC would catch unused static non-inline functions, but it would weaken Clang as a standalone compiler, at least. Hence, here is a counter implementation. The current problem is, W=... only controls compiler flags, which are globally effective. There is no way to address only 'static inline' functions. This commit defines KBUILD_EXTRA_WARN[123] corresponding to W=[123]. When KBUILD_EXTRA_WARN1 is defined, __maybe_unused is omitted from the 'inline' macro. The new macro __inline_maybe_unused makes the code a bit uglier, so I hope we can remove it entirely after fixing most of the warnings. If you contribute to code clean-up, please run "make CC=clang W=1" and check -Wunused-function warnings. You will find lots of unused functions. Some of them are false-positives because the call-sites are disabled by #ifdef. I do not like to abuse the inline keyword for suppressing unused-function warnings because it is intended to be a hint for the compiler optimization. I prefer #ifdef around the definition, or __maybe_unused if #ifdef would make the code too ugly. Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> Tested-by: Nathan Chancellor <natechancellor@gmail.com> --- Changes in v2: - Rebase on top of https://patchwork.kernel.org/patch/11124933/ include/linux/compiler_types.h | 20 ++++++++++++++------ scripts/Makefile.extrawarn | 6 ++++++ 2 files changed, 20 insertions(+), 6 deletions(-) -- 2.17.1