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Date:   Wed, 9 Jan 2019 23:16:25 +0000
From:   Paul Burton <>
To:     "" <>
CC:     "" <>,
        "" <>,
        Paul Burton <>,
        Geert Uytterhoeven <>,
        Masahiro Yamada <>,
        Nicholas Piggin <>,
        "" <>
Subject: [PATCH] kbuild: Disable LD_DEAD_CODE_DATA_ELIMINATION with ftrace &
 GCC <= 4.7

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:

    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 <>
Fixes: e85d1d65cd8a ("kbuild: test dead code/data elimination support in Kconfig")
Reported-by: Geert Uytterhoeven <>
Cc: Masahiro Yamada <>
Cc: Nicholas Piggin <>
Cc: # v4.19+
 init/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/init/Kconfig b/init/Kconfig
index d47cb77a220e..c787f782148d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1124,6 +1124,7 @@ config LD_DEAD_CODE_DATA_ELIMINATION
 	bool "Dead code and data elimination (EXPERIMENTAL)"
 	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)

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