[PATCH v2 1/3] gcc-plugins: Force full rebuild when plugins change

[Kees Cook]

There was no dependency between the plugins changing and the rest of the
kernel being built. Enforce this by including a synthetic header file
when using plugins, that is regenerated any time the plugins are built.

This cannot be included via '-include ...' because Makefiles use the
"filter-out" string function, which removes individual words. Removing
all instances of "-include" from the CFLAGS will cause a lot of
problems. :)

Instead, use -I to include the gcc-plugins directory, and depend on the
new -DGCC_PLUGINS_ENABLED flag to include the generated header file via
include/linux/compiler-version.h, which is already being used to control
full rebuilds. The UM build requires that the -I be explicitly added.

Signed-off-by: Kees Cook <kees@xxxxxxxxxx>
---
Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
Cc: Nicolas Schier <nicolas.schier@xxxxxxxxx>
Cc: <linux-hardening@xxxxxxxxxxxxxxx>
Cc: <linux-kbuild@xxxxxxxxxxxxxxx>
---
 arch/um/Makefile                 | 1 +
 include/linux/compiler-version.h | 4 ++++
 scripts/Makefile.gcc-plugins     | 2 +-
 scripts/gcc-plugins/Makefile     | 8 ++++++++
 4 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/um/Makefile b/arch/um/Makefile
index 1d36a613aad8..8cc0f22ebefa 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -72,6 +72,7 @@ USER_CFLAGS = $(patsubst $(KERNEL_DEFINES),,$(patsubst -I%,,$(KBUILD_CFLAGS))) \
 		$(ARCH_INCLUDE) $(MODE_INCLUDE) $(filter -I%,$(CFLAGS)) \
 		-D_FILE_OFFSET_BITS=64 -idirafter $(srctree)/include \
 		-idirafter $(objtree)/include -D__KERNEL__ -D__UM_HOST__ \
+		-I$(objtree)/scripts/gcc-plugins \
 		-include $(srctree)/include/linux/compiler-version.h \
 		-include $(srctree)/include/linux/kconfig.h
 
diff --git a/include/linux/compiler-version.h b/include/linux/compiler-version.h
index 573fa85b6c0c..08943df04ebb 100644
--- a/include/linux/compiler-version.h
+++ b/include/linux/compiler-version.h
@@ -12,3 +12,7 @@
  * and add dependency on include/config/CC_VERSION_TEXT, which is touched
  * by Kconfig when the version string from the compiler changes.
  */
+
+#ifdef GCC_PLUGINS_ENABLED
+#include "gcc-plugins-deps.h"
+#endif
diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
index 5b8a8378ca8a..468bb8faa9d1 100644
--- a/scripts/Makefile.gcc-plugins
+++ b/scripts/Makefile.gcc-plugins
@@ -38,7 +38,7 @@ export DISABLE_STACKLEAK_PLUGIN
 
 # All the plugin CFLAGS are collected here in case a build target needs to
 # filter them out of the KBUILD_CFLAGS.
-GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y))
+GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y)) -I$(objtree)/scripts/gcc-plugins -DGCC_PLUGINS_ENABLED
 export GCC_PLUGINS_CFLAGS
 
 # Add the flags to the build!
diff --git a/scripts/gcc-plugins/Makefile b/scripts/gcc-plugins/Makefile
index 320afd3cf8e8..24671d39ec90 100644
--- a/scripts/gcc-plugins/Makefile
+++ b/scripts/gcc-plugins/Makefile
@@ -66,3 +66,11 @@ quiet_cmd_plugin_cxx_o_c = HOSTCXX $@
 
 $(plugin-objs): $(obj)/%.o: $(src)/%.c FORCE
 	$(call if_changed_dep,plugin_cxx_o_c)
+
+quiet_cmd_gcc_plugins_updated = UPDATE  $@
+      cmd_gcc_plugins_updated = echo '/* $^ */' > $(obj)/gcc-plugins-deps.h
+
+$(obj)/gcc-plugins-deps.h: $(plugin-single) $(plugin-multi) FORCE
+	$(call if_changed,gcc_plugins_updated)
+
+always-y += gcc-plugins-deps.h
-- 
2.34.1