linux-kernel - Re: [PATCH] kbuild: consolidate Clang compiler flags

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Message-ID: <CAK7LNAT3ftcuNDfEhecMnfjG0Fkkh42wR7XQ1R9Tkr9OMrzAng@mail.gmail.com>
Date:   Mon, 5 Nov 2018 18:18:25 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Stefan Agner <stefan@...er.ch>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Chris Fries <cfries@...gle.com>, Joel Stanley <joel@....id.au>,
        dja@...ens.net, Michal Marek <michal.lkml@...kovi.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kbuild: consolidate Clang compiler flags

On Mon, Nov 5, 2018 at 6:10 PM Stefan Agner <stefan@...er.ch> wrote:
>
> On 05.11.2018 03:48, Masahiro Yamada wrote:
> > Add basic options for Clang such as --target, --prefix, --gcc-toolchain,
> > -no-integrated-as to a single variable CLANG_FLAGS.
> >
> > Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> > ---
> >
> >  Makefile | 13 ++++++-------
> >  1 file changed, 6 insertions(+), 7 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index 93315eb..58c838a 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -487,18 +487,17 @@ endif
> >
> >  ifneq ($(shell $(CC) --version 2>&1 | head -n 1 | grep clang),)
> >  ifneq ($(CROSS_COMPILE),)
> > -CLANG_TARGET := --target=$(notdir $(CROSS_COMPILE:%-=%))
> > +CLANG_FLAGS  = --target=$(notdir $(CROSS_COMPILE:%-=%))
> >  GCC_TOOLCHAIN_DIR := $(dir $(shell which $(LD)))
> > -CLANG_PREFIX := --prefix=$(GCC_TOOLCHAIN_DIR)
> > +CLANG_FLAGS  += --prefix=$(GCC_TOOLCHAIN_DIR)
>
> So this will expand later now, is this ok?
>
> --
> Stefan
>
> >  GCC_TOOLCHAIN        := $(realpath $(GCC_TOOLCHAIN_DIR)/..)
> >  endif
> >  ifneq ($(GCC_TOOLCHAIN),)
> > -CLANG_GCC_TC := --gcc-toolchain=$(GCC_TOOLCHAIN)
> > +CLANG_FLAGS  += --gcc-toolchain=$(GCC_TOOLCHAIN)
> >  endif
> > -KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) $(CLANG_PREFIX)
> > -KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) $(CLANG_PREFIX)
> > -KBUILD_CFLAGS += $(call cc-option, -no-integrated-as)
> > -KBUILD_AFLAGS += $(call cc-option, -no-integrated-as)
> > +CLANG_FLAGS  += $(call cc-option, -no-integrated-as)
> > +KBUILD_CFLAGS        += $(CLANG_FLAGS)
> > +KBUILD_AFLAGS        += $(CLANG_FLAGS)


CLANG_FLAGS is expanded here because KBUILD_CFLAGS and KBUILD_AFLAGS
are defined by using :=

So, it should be OK, but turning CLANG_FLAGS into a simple variable
will be a little more efficient since $(call cc-option, -no-integrated-as)
is evaluated just once.

(Or, this cc-option may not be necessary any longer.)

Will send v2.


Thanks.




> >  endif
> >
> >  RETPOLINE_CFLAGS_GCC := -mindirect-branch=thunk-extern
> > -mindirect-branch-register



-- 
Best Regards
Masahiro Yamada