diff options
authorMasahiro Yamada <>2020-04-23 23:23:52 +0900
committerMasahiro Yamada <>2020-05-12 13:28:33 +0900
commit8b59cd81dc5e724eaea283fa6006985891c7bff4 (patch)
parente33ae3ed331a5cfa24b2abe483f7f4b27bb99c06 (diff)
kbuild: ensure full rebuild when the compiler is updated
Commit 21c54b774744 ("kconfig: show compiler version text in the top comment") added the environment variable, CC_VERSION_TEXT in the comment of the top Kconfig file. It can detect the compiler update, and invoke the syncconfig because all environment variables referenced in Kconfig files are recorded in include/config/auto.conf.cmd This commit makes it a CONFIG option in order to ensure the full rebuild when the compiler is updated. This works like follows: include/config/kconfig.h contains "CONFIG_CC_VERSION_TEXT" in the comment block. The top Makefile specifies "-include $(srctree)/include/linux/kconfig.h" to guarantee it is included from all kernel source files. fixdep parses every source file and all headers included from it, searching for words prefixed with "CONFIG_". Then, fixdep finds CONFIG_CC_VERSION_TEXT in include/config/kconfig.h and adds include/config/cc/version/text.h into every .*.cmd file. When the compiler is updated, syncconfig is invoked because init/Kconfig contains the reference to the environment variable CC_VERTION_TEXT. CONFIG_CC_VERSION_TEXT is updated to the new version string, and include/config/cc/version/text.h is touched. In the next rebuild, Make will rebuild every files since the timestamp of include/config/cc/version/text.h is newer than that of target. Signed-off-by: Masahiro Yamada <>
3 files changed, 19 insertions, 2 deletions
diff --git a/Kconfig b/Kconfig
index e10b3ee084d4..745bc773f567 100644
--- a/Kconfig
+++ b/Kconfig
@@ -5,8 +5,6 @@
mainmenu "Linux/$(ARCH) $(KERNELVERSION) Kernel Configuration"
-comment "Compiler: $(CC_VERSION_TEXT)"
source "scripts/Kconfig.include"
source "init/Kconfig"
diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h
index cc8fa109cfa3..9d12c970f18f 100644
--- a/include/linux/kconfig.h
+++ b/include/linux/kconfig.h
@@ -2,6 +2,8 @@
+/* CONFIG_CC_VERSION_TEXT (Do not delete this comment. See help in Kconfig) */
#include <generated/autoconf.h>
diff --git a/init/Kconfig b/init/Kconfig
index 2bc63a361033..ed1d82c9f1df 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -8,6 +8,23 @@ config DEFCONFIG_LIST
default "/boot/config-$(shell,uname -r)"
default "arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)"
+ string
+ default "$(CC_VERSION_TEXT)"
+ help
+ This is used in unclear ways:
+ - Re-run Kconfig when the compiler is updated
+ The 'default' property references the environment variable,
+ CC_VERSION_TEXT so it is recorded in include/config/auto.conf.cmd.
+ When the compiler is updated, Kconfig will be invoked.
+ - Ensure full rebuild when the compier is updated
+ include/linux/kconfig.h contains this option in the comment line so
+ fixdep adds include/config/cc/version/text.h into the auto-generated
+ dependency. When the compiler is updated, syncconfig will touch it
+ and then every file will be rebuilt.
config CC_IS_GCC
def_bool $(success,echo "$(CC_VERSION_TEXT)" | grep -q gcc)