linux-kernel - [PATCH 4.20 060/111] kbuild: Disable LD_DEAD_CODE_DATA

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Message-Id: <20190121122502.631722437@linuxfoundation.org>
Date:   Mon, 21 Jan 2019 14:42:54 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Paul Burton <paul.burton@...s.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: [PATCH 4.20 060/111] kbuild: Disable LD_DEAD_CODE_DATA_ELIMINATION with ftrace & GCC <= 4.7

4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Paul Burton <paul.burton@...s.com>

commit 16fd20aa98080c2fa666dc384036ec08c80af710 upstream.

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: Nicholas Piggin <npiggin@...il.com>
Cc: stable@...r.kernel.org # v4.19+
Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 init/Kconfig |    1 +
 1 file changed, 1 insertion(+)

--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1130,6 +1130,7 @@ config LD_DEAD_CODE_DATA_ELIMINATION
 	bool "Dead code and data elimination (EXPERIMENTAL)"
 	depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION
 	depends on EXPERT
+	depends on !(FUNCTION_TRACER && CC_IS_GCC && GCC_VERSION < 40800)
 	depends on $(cc-option,-ffunction-sections -fdata-sections)
 	depends on $(ld-option,--gc-sections)
 	help