linux-kernel - [PATCH 4.4 32/37] Kbuild: change CC_OPTIMIZE_FOR

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Date:   Tue,  5 Jun 2018 19:01:37 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Michal Marek <mmarek@...e.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH 4.4 32/37] Kbuild: change CC_OPTIMIZE_FOR_SIZE definition

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

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

From: Arnd Bergmann <arnd@...db.de>

commit 877417e6ffb9578e8580abf76a71e15732473456 upstream.

CC_OPTIMIZE_FOR_SIZE disables the often useful -Wmaybe-unused warning,
because that causes a ridiculous amount of false positives when combined
with -Os.

This means a lot of warnings don't show up in testing by the developers
that should see them with an 'allmodconfig' kernel that has
CC_OPTIMIZE_FOR_SIZE enabled, but only later in randconfig builds
that don't.

This changes the Kconfig logic around CC_OPTIMIZE_FOR_SIZE to make
it a 'choice' statement defaulting to CC_OPTIMIZE_FOR_PERFORMANCE
that gets added for this purpose. The allmodconfig and allyesconfig
kernels now default to -O2 with the maybe-unused warning enabled.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Michal Marek <mmarek@...e.com>
Cc: Nathan Chancellor <natechancellor@...il.com>
Cc: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 init/Kconfig |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1308,6 +1308,17 @@ source "usr/Kconfig"

 endif

+choice
+	prompt "Compiler optimization level"
+	default CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE
+
+config CC_OPTIMIZE_FOR_PERFORMANCE
+	bool "Optimize for performance"
+	help
+	  This is the default optimization level for the kernel, building
+	  with the "-O2" compiler flag for best performance and most
+	  helpful compile-time warnings.
+
 config CC_OPTIMIZE_FOR_SIZE
 	bool "Optimize for size"
 	help
@@ -1316,6 +1327,8 @@ config CC_OPTIMIZE_FOR_SIZE

 	  If unsure, say N.

+endchoice
+
 config SYSCTL
 	bool