Date:   Wed, 4 Oct 2017 12:20:52 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Michal Marek <mmarek@...e.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        groeck@...omium.org, Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Subject: Re: [RFC PATCH 1/2] kbuild: Pass HOSTCC and similar to tools Makefiles

2017-10-04 5:48 GMT+09:00 Douglas Anderson <dianders@...omium.org>:
> The main Linux Makefiles and the tools sub-Makefiles have different
> conventions for passing in CC / CFLAGS.
>
> Here's brief summary for the kernel:
> * CC: target C compiler (must be passed as an argument to make to
>   override)
> * HOSTCC: host C compiler (must be passed as an argument to make to
>   override)
> * CFLAGS: ignored (kernel manages its own CFLAGS)
> * KCFLAGS: extra cflags for the target (expected as an env var)
> * HOSTCFLAGS: host C compiler flags (not modifiable by the caller of
>   make)
>
> Here's a brief summary for the tools:
> * CC: host C compiler (must be passed as an argument to make to
>   override)
> * CFLAGS: base arguments for the host C compiler which are added to by
>   sub builds (expected as an env var)
>
> When the main kernel Makefile calls into the tools Makefile, it should
> adapt things from its syntax to the tools Makefile syntax.
>
> If we don't do this, we have a few issues:
> * If someone wants to user another compiler (like clang, maybe) for
>   hostcc then the tools will still be compiled with gcc.
> * If you happen to be building and you left ${CFLAGS} set to something
>   random (maybe it matches ${CC}, the _target_ C compiler, not the
>   _host_ C compiler) then this random value will be used to compile
>   the tools.
>
> In any case, it seems like it makes sense to pass CC, CFLAGS, and
> similar properly into the tools Makefile.
>
> NOTE: in order to do this properly, we need to add some new
> definitions of HOSTAS and HOSTLD into the main kernel Makefile.  If we
> don't do this and someone overrides "AS" or "LD" on the command line
> then those (which were intended for the target) will be used to build
> host side tools.  We also make up some imaginary "HOSTASFLAGS" and
> "HOSTLDFLAGS".  Someone could specify these, but if they don't at
> least these blank variables will properly clobber ASFLAGS and LDFLAGS
> from the kernel.
>
> This was discovered in the Chrome OS build system where CFLAGS (an
> environment variable) was accidentally left pointing to flags that
> would be an appropriate match to CC.  The kernel didn't use these
> CFLAGS so it was never an issue.  Turning on STACKVALIDATION, however,
> suddenly invoked a tools build that blew up.
>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>
>  Makefile | 30 ++++++++++++++++++++++++++++--
>  1 file changed, 28 insertions(+), 2 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index cf007a31d575..0d3af0677d88 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -298,7 +298,9 @@ HOST_LFS_CFLAGS := $(shell getconf LFS_CFLAGS)
>  HOST_LFS_LDFLAGS := $(shell getconf LFS_LDFLAGS)
>  HOST_LFS_LIBS := $(shell getconf LFS_LIBS)
>
> +HOSTAS       = as
>  HOSTCC       = gcc
> +HOSTLD       = ld
>  HOSTCXX      = g++
>  HOSTCFLAGS   := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 \
>                 -fomit-frame-pointer -std=gnu89 $(HOST_LFS_CFLAGS)
> @@ -1616,11 +1618,35 @@ image_name:
>  # Clear a bunch of variables before executing the submake
>  tools/: FORCE
>         $(Q)mkdir -p $(objtree)/tools
> -       $(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(src)/tools/
> +       $(Q)ASFLAGS="$(HOSTASFLAGS)"\
> +               LDFLAGS="$(HOSTLDFLAGS)" \
> +               CFLAGS="$(HOSTCFLAGS)" \
> +               CXXFLAGS="$(HOSTCXXFLAGS)" \
> +               $(MAKE) \
> +               AS="$(HOSTAS)" \
> +               CC="$(HOSTCC)" \
> +               CXX="$(HOSTCXX)" \
> +               LD="$(HOSTLD)" \
> +               MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" \
> +               O=$(abspath $(objtree)) \
> +               subdir=tools \
> +               -C $(src)/tools/
>
>  tools/%: FORCE
>         $(Q)mkdir -p $(objtree)/tools
> -       $(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(src)/tools/ $*
> +       $(Q)ASFLAGS="$(HOSTASFLAGS)"\
> +               LDFLAGS="$(HOSTLDFLAGS)" \
> +               CFLAGS="$(HOSTCFLAGS)" \
> +               CXXFLAGS="$(HOSTCXXFLAGS)" \
> +               $(MAKE) \
> +               AS="$(HOSTAS)" \
> +               CC="$(HOSTCC)" \
> +               CXX="$(HOSTCXX)" \
> +               LD="$(HOSTLD)" \
> +               MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" \
> +               O=$(abspath $(objtree)) \
> +               subdir=tools \
> +               -C $(src)/tools/ $*
>

Please do not do this.



CC:     for building tools that run on the target machine
HOSTCC: for building tools that run on the build machine


IMHO, this should be consistent to avoid confusion.


Grepping CROSS_COMPILE under tools/ directory,
I see many Makefile expect CC for the target system.

For ex, tools/croup/Makefile

CC = $(CROSS_COMPILE)gcc



Why don't you fix tools/objtool/Makefile ?





-- 
Best Regards
Masahiro Yamada

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