linux-kernel - Re: [PATCH] kbuild: add some extra warning flags unconditionally

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Message-ID: <CAK7LNATgQaHU+6WiMvx0AAf=9AJ5nrL8f8=SJMOCJNQNb_=X1w@mail.gmail.com>
Date:   Thu, 9 May 2019 16:25:11 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Sedat Dilek <sedat.dilek@...il.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kbuild: add some extra warning flags unconditionally

On Thu, May 9, 2019 at 4:11 PM Sedat Dilek <sedat.dilek@...il.com> wrote:
>
> On Thu, May 9, 2019 at 8:47 AM Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
> >
> > These flags are documented in the GCC 4.6 manual, and recognized by
> > Clang as well. Let's rip off the cc-option / cc-disable-warning switches.
> >
>
> BTW, is this a speedup when doing CC/LD FLAGS etc checks unconditionally?

Yes.
cc-option is somewhat costly because it invoked the compiler to
check if the given flag is supported.

So, I want to get rid of as many cc-option calls as possible.


> Asking in general - do you have any numbers :-)?

Removing a couple of cc-options does not make
a measurable difference in general use-cases.

But, this might be more beneficial for chrome OS
because $(CC) is a wrapper and invoking it is much more expensive.




>
> - Sedat -
>
> > Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> > ---
> >
> >  scripts/Makefile.extrawarn | 13 +++++++------
> >  1 file changed, 7 insertions(+), 6 deletions(-)
> >
> > diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> > index 523c4cafe2dc..3ab8d1a303cd 100644
> > --- a/scripts/Makefile.extrawarn
> > +++ b/scripts/Makefile.extrawarn
> > @@ -23,15 +23,16 @@ warning-  := $(empty)
> >  warning-1 := -Wextra -Wunused -Wno-unused-parameter
> >  warning-1 += -Wmissing-declarations
> >  warning-1 += -Wmissing-format-attribute
> > -warning-1 += $(call cc-option, -Wmissing-prototypes)
> > +warning-1 += -Wmissing-prototypes
> >  warning-1 += -Wold-style-definition
> > -warning-1 += $(call cc-option, -Wmissing-include-dirs)
> > +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)
> > -warning-1 += $(call cc-disable-warning, missing-field-initializers)
> > -warning-1 += $(call cc-disable-warning, sign-compare)
> > +# The following turn off the warnings enabled by -Wextra
> > +warning-1 += -Wno-missing-field-initializers
> > +warning-1 += -Wno-sign-compare
> >
> >  warning-2 := -Waggregate-return
> >  warning-2 += -Wcast-align
> > @@ -39,8 +40,8 @@ warning-2 += -Wdisabled-optimization
> >  warning-2 += -Wnested-externs
> >  warning-2 += -Wshadow
> >  warning-2 += $(call cc-option, -Wlogical-op)
> > -warning-2 += $(call cc-option, -Wmissing-field-initializers)
> > -warning-2 += $(call cc-option, -Wsign-compare)
> > +warning-2 += -Wmissing-field-initializers
> > +warning-2 += -Wsign-compare
> >  warning-2 += $(call cc-option, -Wmaybe-uninitialized)
> >  warning-2 += $(call cc-option, -Wunused-macros)
> >
> > --
> > 2.17.1
> >
> > --
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-- 
Best Regards
Masahiro Yamada