linux-kernel - [RFC PATCH 5/7] kconfig: invoke silentoldconfig when compiler is updated

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Date:   Fri,  9 Feb 2018 01:19:10 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     linux-kbuild@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        "Luis R . Rodriguez" <mcgrof@...e.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Ulf Magnusson <ulfalizer@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Pavel Machek <pavel@....cz>, linux-s390@...r.kernel.org,
        Jiri Kosina <jkosina@...e.cz>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-kernel@...r.kernel.org
Subject: [RFC PATCH 5/7] kconfig: invoke silentoldconfig when compiler is updated

Moving compiler option tests to Kconfig means you need to re-run
Kconfig when you update your compiler.  All CC_HAS_... symbols
and other symbols that depend on them must be re-calculated.

It will be nice to detect the compiler update and automatically
invoke silentoldconfig.

This can be done by adding one environment.  With this, silentoldconfig
will add something like follows into include/config/auto.conf.cmd:

ifneq "$(CC_VERSION_TEXT)" "gcc (Ubuntu 5.4.0-6ubuntu1~16.04.6) 5.4.0 20160609"
include/config/auto.conf: FORCE
endif

CC_VERSION_TEXT contains the first line of "$(CC) --version".  If this text
is changed, silentoldconfig will be invoked.

Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
---

 Makefile     | 2 ++
 init/Kconfig | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/Makefile b/Makefile
index 2ee49c9..9afd617 100644
--- a/Makefile
+++ b/Makefile
@@ -441,6 +441,8 @@ export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
 export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
 export KBUILD_ARFLAGS
 
+export CC_VERSION_TEXT := $(shell $(CC) --version | head -n 1)
+
 # When compiling out-of-tree modules, put MODVERDIR in the module
 # tree rather than in the kernel tree. The kernel tree might
 # even be read-only.
diff --git a/init/Kconfig b/init/Kconfig
index e37f4b2..64f9dd2 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -16,6 +16,15 @@ config DEFCONFIG_LIST
 	default "$ARCH_DEFCONFIG"
 	default "arch/$ARCH/defconfig"
 
+# CC_VERSION_TEXT is needed here to invoke Kconfig when compiler is updated
+config CC_VERSION_TEXT
+	string
+	option env="CC_VERSION_TEXT"
+	help
+	  This is used to detect if the compiler is changed. If the version
+	  text does not match, silentoldconfig will be invoked because we need
+	  to re-compute compiler capabilities and symbols that depends on them.
+
 config CONSTRUCTORS
 	bool
 	depends on !UML
-- 
2.7.4