linux-kernel - Re: [PATCH] kbuild: avoid conflict between -ffunction-sections and -pg on gcc-4.7

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Date:   Wed, 19 Apr 2017 00:31:58 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <mmarek@...e.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kbuild: avoid conflict between -ffunction-sections and
 -pg on gcc-4.7

Hi Arnd,


2017-04-14 15:17 GMT+09:00 Masahiro Yamada <yamada.masahiro@...ionext.com>:
> Arnd Bergmann reported:
>   "When ftrace is enabled and we build with gcc-4.7 or older, we
>   get a warning for each file on architectures that select
>   CONFIG_LD_DEAD_CODE_DATA_ELIMINATION:
>
>   warning: -ffunction-sections disabled; it makes profiling impossible [enabled by default]
>   "
>
> Since commit c3f0d0bc5b01 ("kbuild, LLVMLinux: Add -Werror to
> cc-option to support clang"), warnings are treated as errors in
> cc-option checks.  CC_FLAGS_FTRACE is blindly added to KBUILD_CFLAGS,
> so $(call cc-option,-ffunction-sections,) should be moved below it
> in order to detect the conflict between the two options.
>
> Reported-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
>
>  Makefile | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index efa267a..753e450 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -632,11 +632,6 @@ include arch/$(SRCARCH)/Makefile
>  KBUILD_CFLAGS  += $(call cc-option,-fno-delete-null-pointer-checks,)
>  KBUILD_CFLAGS  += $(call cc-disable-warning,frame-address,)
>
> -ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
> -KBUILD_CFLAGS  += $(call cc-option,-ffunction-sections,)
> -KBUILD_CFLAGS  += $(call cc-option,-fdata-sections,)
> -endif
> -
>  ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
>  KBUILD_CFLAGS  += -Os $(call cc-disable-warning,maybe-uninitialized,)
>  else
> @@ -773,6 +768,11 @@ ifdef CONFIG_DEBUG_SECTION_MISMATCH
>  KBUILD_CFLAGS += $(call cc-option, -fno-inline-functions-called-once)
>  endif
>
> +ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
> +KBUILD_CFLAGS  += $(call cc-option,-ffunction-sections,)
> +KBUILD_CFLAGS  += $(call cc-option,-fdata-sections,)
> +endif
> +
>  # arch Makefile may override CC so keep this after arch Makefile is included
>  NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
>  CHECKFLAGS     += $(NOSTDINC_FLAGS)


I tested this patch, and confirmed it fixed the issue.
So, I will apply this shortly.

I used the following GCC 4.7 for testing:

https://releases.linaro.org/archive/13.04/components/toolchain/binaries/gcc-linaro-arm-linux-gnueabihf-4.7-2013.04-20130415_linux.tar.xz



-- 
Best Regards
Masahiro Yamada