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Date: Thu, 07 Dec 2017 18:16:56 -0800 From: Sodagudi Prasad <psodagud@...eaurora.org> To: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>, Michal Marek <mmarek@...e.com>, Greg Hackmann <ghackmann@...gle.com>, linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: unused-variable warning is getting disabled with clang 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 -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, Linux Foundation Collaborative Project
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