2017-12-08 11:16 GMT+09:00 Sodagudi Prasad <psodagud@xxxxxxxxxxxxxx>: > On 2017-12-06 22:26, Greg Kroah-Hartman wrote: >> >> On Wed, Dec 06, 2017 at 01:24:51PM -0800, Sodagudi Prasad wrote: >>> >>> >>> Hi All, >>> >>> When kernel compiled with clang, following line is disabling the >>> unused-variable warning. This is not the case with gcc. >>> KBUILD_CFLAGS += $(call cc-disable-warning, unused-variable) >>> >>> Are there any specific reasons for disabling unused-variable with clang? >> >> >> Try it and see why it is disabled :) > > > Hi Greg, > > When I have enabled -Wunused-variable warnings with clang, observed both > -Wunused-variable and -Wunused-const-variable as expected. > It looks that, -Wunused-const-variable warnings are disabled explicitly with > GCC as well. > commit - c9c6837d39311b0c - "kbuild: move -Wunused-const-variable to W=1 > warning level" > > I could see following warnings along with couple of -Wunused-variables > warnings with downstream code. > arch/arm64/crypto/sha1-ce-glue.c:118:1: warning: unused variable > 'cpu_feature_match_SHA1' [-Wunused-const-variable] > include/linux/cpufeature.h:48:33: note: expanded from macro > 'module_cpu_feature_match' > arch/arm64/crypto/sha2-ce-glue.c:148:1: warning: unused variable > 'cpu_feature_match_SHA2' [-Wunused-const-variable] > arch/arm64/crypto/ghash-ce-glue.c:597:33: warning: unused variable > 'ghash_cpu_feature' [-Wunused-const-variable] > arch/arm64/crypto/aes-ce-cipher.c:280:1: warning: unused variable > 'cpu_feature_match_AES' [-Wunused-const-variable] > arch/arm64/crypto/aes-glue.c:674:1: warning: unused variable > 'cpu_feature_match_AES' [-Wunused-const-variable] > kernel/trace/ftrace.c:1092:27: warning: unused variable 'ftrace_swapper_pid' > [-Wunused-const-variable] > drivers/usb/host/ehci-platform.c:406:36: warning: unused variable > 'ehci_acpi_match' [-Wunused-const-variable] > drivers/usb/host/xhci-plat.c:416:36: warning: unused variable > 'usb_xhci_acpi_match' [-Wunused-const-variable] > > So I have made following change and I will share patch for the same. > > diff --git a/Makefile b/Makefile > index 4e6da2f..8a6c14e 100644 > --- a/Makefile > +++ b/Makefile > @@ -711,7 +711,7 @@ endif > KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) -meabi gnu > KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) > KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,) > -KBUILD_CFLAGS += $(call cc-disable-warning, unused-variable) > +KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable) > KBUILD_CFLAGS += $(call cc-disable-warning, format-invalid-specifier) > KBUILD_CFLAGS += $(call cc-disable-warning, gnu) > KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) > > Please let me know if you have any concerns with this approach to identify > all unused local variables. > > -Thanks, Prasad This approach seems good, but KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable) will be common for GCC and Clang. Please move it out of "ifeq ... else .. endif" -- Best Regards Masahiro Yamada -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
