linux-kernel - Re: [PATCH v2] kbuild: Disable LD_DEAD_CODE_DATA

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Message-ID: <CAK7LNATEs-+GcVohYPLW3sVMDfpLNtT3dbRYcO5FNqJTf9G5SA@mail.gmail.com>
Date:   Sun, 13 Jan 2019 12:54:17 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Paul Burton <paul.burton@...s.com>
Cc:     "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Paul Burton <pburton@...ecomp.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Nicholas Piggin <npiggin@...il.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v2] kbuild: Disable LD_DEAD_CODE_DATA_ELIMINATION with
 ftrace & GCC <= 4.7

On Sat, Jan 12, 2019 at 6:00 AM Paul Burton <paul.burton@...s.com> wrote:
>
> When building using GCC 4.7 or older, -ffunction-sections & the -pg flag
> used by ftrace are incompatible. This causes warnings or build failures
> (where -Werror applies) such as the following:
>
>   arch/mips/generic/init.c:
>     error: -ffunction-sections disabled; it makes profiling impossible
>
> This used to be taken into account by the ordering of calls to cc-option
> from within the top-level Makefile, which was introduced by commit
> 90ad4052e85c ("kbuild: avoid conflict between -ffunction-sections and
> -pg on gcc-4.7"). Unfortunately this was broken when the
> CONFIG_LD_DEAD_CODE_DATA_ELIMINATION cc-option check was moved to
> Kconfig in commit e85d1d65cd8a ("kbuild: test dead code/data elimination
> support in Kconfig"), because the flags used by this check no longer
> include -pg.
>
> Fix this by not allowing CONFIG_LD_DEAD_CODE_DATA_ELIMINATION to be
> enabled at the same time as ftrace/CONFIG_FUNCTION_TRACER when building
> using GCC 4.7 or older.
>
> Signed-off-by: Paul Burton <paul.burton@...s.com>
> Fixes: e85d1d65cd8a ("kbuild: test dead code/data elimination support in Kconfig")
> Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: stable@...r.kernel.org # v4.19+
> Cc: linux-kbuild@...r.kernel.org
> Cc: linux-mips@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> ---
> Changes in v2:
> - Invert the dependency as Masahiro suggested.


Applied to linux-kbuild/fixes.


Thanks!


-- 
Best Regards
Masahiro Yamada