sancov: Split plugin build from plugin CFLAGS

When the sancov_plugin is enabled, it gets added to gcc-plugin-y which
is used to populate both GCC_PLUGIN (for building the plugin) and
GCC_PLUGINS_CFLAGS (for enabling and options). Instead of adding sancov
to both and then removing it from GCC_PLUGINS_CFLAGS, create a separate
list, gcc-plugin-external-y, which is only added to GCC_PLUGIN.

This will also be used by the coming randstruct build changes.

Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: linux-kbuild@vger.kernel.org
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220503205503.3054173-3-keescook@chromium.org

diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
index f67153b..927c3dd 100644 (file)
--- a/scripts/Makefile.gcc-plugins
+++ b/scripts/Makefile.gcc-plugins
@@ -8,8 +8,6 @@ ifdef CONFIG_GCC_PLUGIN_LATENT_ENTROPY
 endif
 export DISABLE_LATENT_ENTROPY_PLUGIN
 
-gcc-plugin-$(CONFIG_GCC_PLUGIN_SANCOV)         += sancov_plugin.so
-
 gcc-plugin-$(CONFIG_GCC_PLUGIN_STRUCTLEAK)     += structleak_plugin.so
 gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK_VERBOSE)      \
                += -fplugin-arg-structleak_plugin-verbose
@@ -53,13 +51,17 @@ export DISABLE_ARM_SSP_PER_TASK_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))
-# The sancov_plugin.so is included via CFLAGS_KCOV, so it is removed here.
-GCC_PLUGINS_CFLAGS := $(filter-out %/sancov_plugin.so, $(GCC_PLUGINS_CFLAGS))
 export GCC_PLUGINS_CFLAGS
 
 # Add the flags to the build!
 KBUILD_CFLAGS += $(GCC_PLUGINS_CFLAGS)
 
-# All enabled GCC plugins are collected here for building below.
-GCC_PLUGIN := $(gcc-plugin-y)
+# Some plugins are enabled outside of this Makefile, but they still need to
+# be included in GCC_PLUGIN so they can get built.
+gcc-plugin-external-$(CONFIG_GCC_PLUGIN_SANCOV)                        \
+       += sancov_plugin.so
+
+# All enabled GCC plugins are collected here for building in
+# scripts/gcc-scripts/Makefile.
+GCC_PLUGIN := $(gcc-plugin-y) $(gcc-plugin-external-y)
 export GCC_PLUGIN