Message-ID: <CA+icZUWv0vAOSq_4BfbqrTdUSnN_D4ETVfpSHiATokCsY2R9pg@mail.gmail.com>
Date:   Thu, 29 Aug 2019 10:49:47 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Michal Marek <michal.lkml@...kovi.net>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] kbuild: refactor scripts/Makefile.extrawarn

On Thu, Aug 29, 2019 at 12:38 AM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@...glegroups.com> wrote:
>
> On Tue, Aug 27, 2019 at 10:54 PM Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
> >
> > Instead of the warning-[123] magic, let's accumulate compiler options
> > to KBUILD_CFLAGS directly as the top Makefile does. I think this makes
> > easier to understand what is going on in this file.
> >
> > This commit slightly changes the behavior, I think all of which are OK.
> >
> > [1] Currently, cc-option calls are needlessly evaluated. For example,
> >       warning-3 += $(call cc-option, -Wpacked-bitfield-compat)
> >     needs evaluating only when W=3, but it is actually evaluated for
> >     W=1, W=2 as well. With this commit, only relevant cc-option calls
> >     will be evaluated. This is a slight optimization.
> >
> > [2] Currently, unsupported level like W=4 is checked by:
> >       $(error W=$(KBUILD_ENABLE_EXTRA_GCC_CHECKS) is unknown)
> >     This will no longer be checked, but I do not think it is a big
> >     deal.
> >
> > [3] Currently, 4 Clang warnings (Winitializer-overrides, Wformat,
> >     Wsign-compare, Wformat-zero-length) are shown by any of W=1, W=2,
> >     and W=3. With this commit, they will be warned only by W=1. I
> >     think this is a more correct behavior since each warning belongs
> >     to only one warning level.
> >
> > Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> > ---
> >
> >  scripts/Makefile.extrawarn | 104 +++++++++++++++++++------------------
> >  1 file changed, 53 insertions(+), 51 deletions(-)
> >
> > diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> > index a74ce2e3c33e..1fa53968e292 100644
> > --- a/scripts/Makefile.extrawarn
> > +++ b/scripts/Makefile.extrawarn
> > @@ -1,14 +1,6 @@
> >  # SPDX-License-Identifier: GPL-2.0
> >  # ==========================================================================
> > -#
> >  # make W=... settings
> > -#
> > -# W=1 - warnings that may be relevant and does not occur too often
> > -# W=2 - warnings that occur quite often but may still be relevant
> > -# W=3 - the more obscure warnings, can most likely be ignored
> > -#
> > -# $(call cc-option, -W...) handles gcc -W.. options which
> > -# are not supported by all versions of the compiler
> >  # ==========================================================================
> >
> >  KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
> > @@ -17,58 +9,68 @@ ifeq ("$(origin W)", "command line")
> >    export KBUILD_ENABLE_EXTRA_GCC_CHECKS := $(W)
> >  endif
> >
> > -ifdef KBUILD_ENABLE_EXTRA_GCC_CHECKS
> > -warning-  := $(empty)
> > +#
> > +# W=1 - warnings that may be relevant and does not occur too often
> > +#
> > +ifneq ($(findstring 1, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
> >
> > -warning-1 := -Wextra -Wunused -Wno-unused-parameter
> > -warning-1 += -Wmissing-declarations
> > -warning-1 += -Wmissing-format-attribute
> > -warning-1 += -Wmissing-prototypes
> > -warning-1 += -Wold-style-definition
> > -warning-1 += -Wmissing-include-dirs
> > -warning-1 += $(call cc-option, -Wunused-but-set-variable)
> > -warning-1 += $(call cc-option, -Wunused-const-variable)
> > -warning-1 += $(call cc-option, -Wpacked-not-aligned)
> > -warning-1 += $(call cc-option, -Wstringop-truncation)
> > +KBUILD_CFLAGS += -Wextra -Wunused -Wno-unused-parameter
> > +KBUILD_CFLAGS += -Wmissing-declarations
> > +KBUILD_CFLAGS += -Wmissing-format-attribute
> > +KBUILD_CFLAGS += -Wmissing-prototypes
> > +KBUILD_CFLAGS += -Wold-style-definition
> > +KBUILD_CFLAGS += -Wmissing-include-dirs
> > +KBUILD_CFLAGS += $(call cc-option, -Wunused-but-set-variable)
> > +KBUILD_CFLAGS += $(call cc-option, -Wunused-const-variable)
> > +KBUILD_CFLAGS += $(call cc-option, -Wpacked-not-aligned)
> > +KBUILD_CFLAGS += $(call cc-option, -Wstringop-truncation)
> >  # The following turn off the warnings enabled by -Wextra
> > -warning-1 += -Wno-missing-field-initializers
> > -warning-1 += -Wno-sign-compare
> > -
> > -warning-2 += -Wcast-align
> > -warning-2 += -Wdisabled-optimization
> > -warning-2 += -Wnested-externs
> > -warning-2 += -Wshadow
> > -warning-2 += $(call cc-option, -Wlogical-op)
> > -warning-2 += -Wmissing-field-initializers
> > -warning-2 += -Wsign-compare
> > -warning-2 += $(call cc-option, -Wmaybe-uninitialized)
> > -warning-2 += $(call cc-option, -Wunused-macros)
> > -
> > -warning-3 := -Wbad-function-cast
> > -warning-3 += -Wcast-qual
> > -warning-3 += -Wconversion
> > -warning-3 += -Wpacked
> > -warning-3 += -Wpadded
> > -warning-3 += -Wpointer-arith
> > -warning-3 += -Wredundant-decls
> > -warning-3 += -Wswitch-default
> > -warning-3 += $(call cc-option, -Wpacked-bitfield-compat)
> > -
> > -warning := $(warning-$(findstring 1, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
> > -warning += $(warning-$(findstring 2, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
> > -warning += $(warning-$(findstring 3, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
> > -
> > -ifeq ("$(strip $(warning))","")
> > -        $(error W=$(KBUILD_ENABLE_EXTRA_GCC_CHECKS) is unknown)
> > -endif
> > +KBUILD_CFLAGS += -Wno-missing-field-initializers
> > +KBUILD_CFLAGS += -Wno-sign-compare
> >
> > -KBUILD_CFLAGS += $(warning)
> >  else
> >
> > +# W=1 also stops suppressing some warnings
> > +
> >  ifdef CONFIG_CC_IS_CLANG
> >  KBUILD_CFLAGS += -Wno-initializer-overrides
> >  KBUILD_CFLAGS += -Wno-format
> >  KBUILD_CFLAGS += -Wno-sign-compare
> >  KBUILD_CFLAGS += -Wno-format-zero-length
> >  endif
>
> I find this part of the patch exceedingly confusing, and I think it
> mistakenly changes the behavior of W=2, W=3, and W=4.  If W != 1 && CC
> == clang, then disable some flags?  What?  So W=2,3,4 those are
> disabled, but at W=1 are not?  Didn't the previous version set these
> unless any W= was set?
>
> > +
> > +endif
> > +
> > +#
> > +# W=2 - warnings that occur quite often but may still be relevant
> > +#
> > +ifneq ($(findstring 2, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
> > +
> > +KBUILD_CFLAGS += -Wcast-align
> > +KBUILD_CFLAGS += -Wdisabled-optimization
> > +KBUILD_CFLAGS += -Wnested-externs
> > +KBUILD_CFLAGS += -Wshadow
> > +KBUILD_CFLAGS += $(call cc-option, -Wlogical-op)
> > +KBUILD_CFLAGS += -Wmissing-field-initializers
> > +KBUILD_CFLAGS += -Wsign-compare
> > +KBUILD_CFLAGS += $(call cc-option, -Wmaybe-uninitialized)
> > +KBUILD_CFLAGS += $(call cc-option, -Wunused-macros)
> > +
> > +endif
> > +
> > +#
> > +# W=3 - the more obscure warnings, can most likely be ignored
> > +#
> > +ifneq ($(findstring 3, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
> > +
> > +KBUILD_CFLAGS += -Wbad-function-cast
> > +KBUILD_CFLAGS += -Wcast-qual
> > +KBUILD_CFLAGS += -Wconversion
> > +KBUILD_CFLAGS += -Wpacked
> > +KBUILD_CFLAGS += -Wpadded
> > +KBUILD_CFLAGS += -Wpointer-arith
> > +KBUILD_CFLAGS += -Wredundant-decls
> > +KBUILD_CFLAGS += -Wswitch-default
> > +KBUILD_CFLAGS += $(call cc-option, -Wpacked-bitfield-compat)
> > +
> >  endif
> > --
> > 2.17.1
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers

Just a quick test...

...with clang-9 (built with tc-build from llvm-project.git#release/9.x)

$ mycompiler --version
ClangBuiltLinux clang version 9.0.0
(git://github.com/llvm/llvm-project
e82a53603ae3fed2215a44b5ac603db00a780c02) (based on LLVM 9.0.0)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/sdi/src/llvm-toolchain/install/bin

$ mylinker --version
LLD 9.0.0 (git://github.com/llvm/llvm-project
e82a53603ae3fed2215a44b5ac603db00a780c02) (compatible with GNU
linkers)

With each run (changing W=...), I stopped my build-script manually,
that's why the numbers differ.

[ NO W-N ]

sdi@...za:~/src/linux-kernel$ for i in Wno-initializer-overrides
Wno-format Wno-sign-compare Wno-format-zero-length ; do echo [ $i ] ;
grep $i build-log_5.3.0-rc6-2-amd64-cbl-asmgoto.txt_NO-W-N | wc -l ;
done
[ Wno-initializer-overrides ]
178
[ Wno-format ]
178
[ Wno-sign-compare ]
178
[ Wno-format-zero-length ]
178

[ W=1 ]

sdi@...za:~/src/linux-kernel$ for i in Wno-initializer-overrides
Wno-format Wno-sign-compare Wno-format-zero-length ; do echo [ $i ] ;
grep $i build-log_5.3.0-rc6-2-amd64-cbl-asmgoto.txt_W-1 | wc -l ; done
[ Wno-initializer-overrides ]
0
[ Wno-format ]
169
[ Wno-sign-compare ]
169
[ Wno-format-zero-length ]
0

[ W=2 ]

sdi@...za:~/src/linux-kernel$ for i in Wno-initializer-overrides
Wno-format Wno-sign-compare Wno-format-zero-length ; do echo [ $i ] ;
grep $i build-log_5.3.0-rc6-2-amd64-cbl-asmgoto.txt_W-2 | wc -l ; done
[ Wno-initializer-overrides ]
129
[ Wno-format ]
129
[ Wno-sign-compare ]
129
[ Wno-format-zero-length ]
129

[ W=3 ]

sdi@...za:~/src/linux-kernel$ for i in Wno-initializer-overrides
Wno-format Wno-sign-compare Wno-format-zero-length ; do echo [ $i ] ;
grep $i build-log_5.3.0-rc6-2-amd64-cbl-asmgoto.txt_W-3 | wc -l ; done
[ Wno-initializer-overrides ]
114
[ Wno-format ]
114
[ Wno-sign-compare ]
114
[ Wno-format-zero-length ]
114

[ W=4 ]

sdi@...za:~/src/linux-kernel$ for i in Wno-initializer-overrides
Wno-format Wno-sign-compare Wno-format-zero-length ; do echo [ $i ] ;
grep $i build-log_5.3.0-rc6-2-amd64-cbl-asmgoto.txt_W-4 | wc -l ; done
[ Wno-initializer-overrides ]
495
[ Wno-format ]
495
[ Wno-sign-compare ]
495
[ Wno-format-zero-length ]
495

W=1 is not passing -Wno-initializer-overrides and -Wno-format-zero-length.
Unsure if other KBUILD_CFLAGS  in W=1 disables them.

So, if it is desired to pass the CLANG extrawarn compiler-options to
all W=... then I ask myself why the CLANG block is in the W=1 block
only?
So if CLANG extrawarn options are independent of any W=... make-option
then I prefer to put it in a seperate block with an appropriate
comment.

According to the commit message W=4 is unsupported, but I can do a
'make V=1 W=4'.
If I pass an unsupported value to W=... then I expect an warning or
info or exit or whatever.

My €0,02.

- Sedat -

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