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Message-ID: <5fd58e1e-9e5f-4bd7-2153-aa0055a3f6c5@csgroup.eu>
Date: Wed, 14 Jun 2023 18:26:18 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Nick Desaulniers <ndesaulniers@...gle.com>
CC: kernel test robot <lkp@...el.com>,
"llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
"oe-kbuild-all@...ts.linux.dev" <oe-kbuild-all@...ts.linux.dev>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Michael Ellerman <mpe@...erman.id.au>,
Nathan Chancellor <nathan@...nel.org>
Subject: Re: arch/powerpc/math-emu/fcmpu.c:13:2: warning: variable 'A_c' set
but not used
Le 14/06/2023 à 18:04, Nick Desaulniers a écrit :
> On Wed, Jun 14, 2023 at 10:11 AM Christophe Leroy
> <christophe.leroy@...roup.eu> wrote:
>>
>> Hi,
>>
>> Le 22/05/2023 à 21:00, kernel test robot a écrit :
>>> Hi Christophe,
>>>
>>> FYI, the error/warning still remains.
>>>
>>> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>>> head: 44c026a73be8038f03dbdeef028b642880cf1511
>>> commit: 7245fc5bb7a966852d5bd7779d1f5855530b461a powerpc/math-emu: Remove -w build flag and fix warnings
>>> date: 9 months ago
>>> config: powerpc-randconfig-r022-20230522 (https://download.01.org/0day-ci/archive/20230523/202305230231.3Wb7Q68G-lkp@intel.com/config)
>>> compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project b0fb98227c90adf2536c9ad644a74d5e92961111)
>>> reproduce (this is a W=1 build):
>>> wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>>> chmod +x ~/bin/make.cross
>>> # install powerpc cross compiling tool for clang build
>>> # apt-get install binutils-powerpc-linux-gnu
>>> # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7245fc5bb7a966852d5bd7779d1f5855530b461a
>>> git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>>> git fetch --no-tags linus master
>>> git checkout 7245fc5bb7a966852d5bd7779d1f5855530b461a
>>> # save the config file
>>> mkdir build_dir && cp config build_dir/.config
>>> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=powerpc olddefconfig
>>> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=powerpc SHELL=/bin/bash arch/powerpc/math-emu/
>>>
>>> If you fix the issue, kindly add following tag where applicable
>>> | Reported-by: kernel test robot <lkp@...el.com>
>>> | Closes: https://lore.kernel.org/oe-kbuild-all/202305230231.3Wb7Q68G-lkp@intel.com/
>>>
>>> All warnings (new ones prefixed by >>):
>>>
>>>>> arch/powerpc/math-emu/fcmpu.c:13:2: warning: variable 'A_c' set but not used [-Wunused-but-set-variable]
>>
>> This code is imported, and there is no plan to make any change to it.
>> Can you desactivate that warning ?
>
> If the code is imported, and we don't plan to push fixes upstream,
> does it make sense to just set -Wno-unusued-but-set-variable in
> arch/powerpc/math-emu/Makefile?
Yes, that's done already but clang ignores it apparently.
>
> Wait, what?!
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/math-emu/Makefile#n20
> arch/powerpc/math-emu/Makefile already has -Wunused-but-set-variable
> in ccflags-remove-y. But if KBUILD_EXTRA_WARN is set for W=1 builds,
> -Wunused-but-set-variable is added back, but only for math.o and
> math_efp.o. The warning above comes from building fcmpu.o. So how
> did -Wunused-but-set-variable get set in the first place?
Indeed.
I looked once more and found out that:
clang -Wp,-MMD,arch/powerpc/math-emu/.fcmpu.o.d -nostdinc
-I./arch/powerpc/include -I./arch/powerpc/include/generated -I./include
-I./arch/powerpc/include/uapi -I./arch/powerpc/include/generated/uapi
-I./include/uapi -I./include/generated/uapi -include
./include/linux/compiler-version.h -include ./include/linux/kconfig.h
-include ./include/linux/compiler_types.h -D__KERNEL__ -I ./arch/powerpc
-DHAVE_AS_ATHIGH=1 -fmacro-prefix-map=./= -Wundef -DKBUILD_EXTRA_WARN1
-Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs
-fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE
-Werror=implicit-function-declaration -Werror=implicit-int
-Werror=return-type -Wno-format-security -funsigned-char -std=gnu11
--target=powerpc64le-linux-gnu -fintegrated-as
-Werror=unknown-warning-option -Werror=ignored-optimization-argument
-Werror=option-ignored -Werror=unused-command-line-argument -mbig-endian
-m32 -msoft-float -pipe -mcpu=powerpc -mno-prefixed -mno-pcrel
-mno-altivec -mno-vsx -mno-mma -mno-spe -fno-asynchronous-unwind-tables
-mbig-endian -fno-delete-null-pointer-checks -Wno-frame-address
-Wno-address-of-packed-member -O2 -Wframe-larger-than=1024
-fno-stack-protector -Wno-gnu -Wno-unused-but-set-variable
-Wno-unused-const-variable -ftrivial-auto-var-init=zero
-enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang
-pg -Wdeclaration-after-statement -Wvla -Wno-pointer-sign
-Wcast-function-type -Wimplicit-fallthrough -fno-strict-overflow
-fno-stack-check -Werror=date-time -Werror=incompatible-pointer-types
-Wextra -Wunused -Wno-unused-parameter -Wmissing-format-attribute
-Wold-style-definition -Wmissing-include-dirs -Wunused-const-variable
-Wno-missing-field-initializers -Wno-sign-compare -Wno-type-limits
-Wno-shift-negative-value -g -Werror
-DKBUILD_MODFILE='"arch/powerpc/math-emu/fcmpu"'
-DKBUILD_BASENAME='"fcmpu"' -DKBUILD_MODNAME='"fcmpu"'
-D__KBUILD_MODNAME=kmod_fcmpu -c -o arch/powerpc/math-emu/fcmpu.o
arch/powerpc/math-emu/fcmpu.c ; ./tools/objtool/objtool --mcount
--uaccess --sec-address arch/powerpc/math-emu/fcmpu.o
If you move -Wunused before -Wno-unused-but-set-variable, then you don't
have the warning/error anymore. So what ? What the hell is clang
behaving that way ?
GCC documentation is explicit, see
https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html :
The combined effect of positive and negative forms is that more
specific options have priority over less specific ones, independently of
their position in the command-line.
Can clang be fixed ?
Christophe
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