[PATCH] [RFC] Add additional include path for gcc plugins

[Dan Li]

When kernel enables gcc plugin, some header files are missing in some
tool chains (as in the following example)

These header files can be found in other toolchains, and sometimes
the md5hash of these files are same(in most versions).

Should we add a parameter to plugin to allow users to import their own
header file directories?

---
  HOSTCXX scripts/gcc-plugins/stackleak_plugin.so
In file included from scripts/gcc-plugins/gcc-common.h:103:0,
                 from scripts/gcc-plugins/stackleak_plugin.c:30:
/workspace/gcc-arm-9.2-2019.12-x86_64-aarch64-none-linux-gnu/bin/../
lib/gcc/aarch64-none-linux-gnu/9.2.1/plugin/include/builtins.h:23:17:
 fatal error: mpc.h: No such file or directory
 #include <mpc.h>

Signed-off-by: Dan Li <ashimida@xxxxxxxxxxxxxxxxx>
---
 Makefile                     | 3 +++
 scripts/gcc-plugins/Makefile | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 09bb314..e6134f3 100644
--- a/Makefile
+++ b/Makefile
@@ -1036,6 +1036,9 @@ include-$(CONFIG_UBSAN)		+= scripts/Makefile.ubsan
 include-$(CONFIG_KCOV)		+= scripts/Makefile.kcov
 include-$(CONFIG_GCC_PLUGINS)	+= scripts/Makefile.gcc-plugins
 
+GCC_PLUGINS_EXT_CFLAGS=
+export GCC_PLUGINS_EXT_CFLAGS
+
 include $(addprefix $(srctree)/, $(include-y))
 
 # scripts/Makefile.gcc-plugins is intentionally included last.
diff --git a/scripts/gcc-plugins/Makefile b/scripts/gcc-plugins/Makefile
index 1952d3b..0b3e27a 100644
--- a/scripts/gcc-plugins/Makefile
+++ b/scripts/gcc-plugins/Makefile
@@ -23,7 +23,7 @@ GCC_PLUGINS_DIR = $(shell $(CC) -print-file-name=plugin)
 
 plugin_cxxflags	= -Wp,-MMD,$(depfile) $(KBUILD_HOSTCXXFLAGS) -fPIC \
 		  -include $(srctree)/include/linux/compiler-version.h \
-		   -I $(GCC_PLUGINS_DIR)/include -I $(obj) -std=gnu++11 \
+		   -I $(GCC_PLUGINS_DIR)/include -I $(obj) $(GCC_PLUGINS_EXT_CFLAGS) -std=gnu++11 \
 		   -fno-rtti -fno-exceptions -fasynchronous-unwind-tables \
 		   -ggdb -Wno-narrowing -Wno-unused-variable \
 		   -Wno-format-diag
-- 
2.7.4