linux-kernel - [PATCH] kbuild: disable -ffunction-sections on gcc-4.7 with ftrace

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Date:   Fri, 16 Dec 2016 10:24:53 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Michal Marek <mmarek@...e.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Kees Cook <keescook@...omium.org>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] kbuild: disable -ffunction-sections on gcc-4.7 with ftrace

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]

This turns off function sections in that specific case, leaving
it enabled for all other configurations.

Fixes: b67067f1176d ("kbuild: allow archs to select link dead code/data elimination")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Makefile b/Makefile
index 4fb4b889c862..7dfd0aa4f3f7 100644
--- a/Makefile
+++ b/Makefile
@@ -638,7 +638,11 @@ 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
+ifdef CONFIG_FUNCTION_TRACER
+KBUILD_CFLAGS	+= $(call cc-ifversion, -ge,0409,$(call cc-option,-ffunction-sections,))
+else
 KBUILD_CFLAGS	+= $(call cc-option,-ffunction-sections,)
+endif
 KBUILD_CFLAGS	+= $(call cc-option,-fdata-sections,)
 endif
 
-- 
2.9.0