kbuild: move host .so build rules to scripts/gcc-plugins/Makefile

The host shared library rules are currently implemented in
scripts/Makefile.host, but actually GCC-plugin is the only user of
them. (The VDSO .so files are built for the target by different
build rules) Hence, they do not need to be treewide available.

Move all the relevant build rules to scripts/gcc-plugins/Makefile.

I also optimized the build steps so *.so is directly built from .c
because every upstream plugin is compiled from a single source file.

I am still keeping the multi-file plugin support, which Kees Cook
mentioned might be needed by out-of-tree plugins.
(https://lkml.org/lkml/2019/1/11/1107)

If the plugin, foo.so, is compiled from two files foo.c and foo2.c,
then you can do like follows:

  foo-objs := foo.o foo2.o

Single-file plugins do not need the *-objs notation.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Kees Cook <keescook@chromium.org>

1 files changed, 50 insertions, 11 deletions

diff --git a/scripts/gcc-plugins/Makefile b/scripts/gcc-plugins/Makefile
index 4014ba7e2fbd..d66949bfeba4 100644
--- a/scripts/gcc-plugins/Makefile
+++ b/scripts/gcc-plugins/Makefile
@@ -1,22 +1,61 @@
 # SPDX-License-Identifier: GPL-2.0
-GCC_PLUGINS_DIR := $(shell $(CC) -print-file-name=plugin)
 
-HOST_EXTRACXXFLAGS += -I$(GCC_PLUGINS_DIR)/include -I$(src) -std=gnu++98 -fno-rtti
-HOST_EXTRACXXFLAGS += -fno-exceptions -fasynchronous-unwind-tables -ggdb
-HOST_EXTRACXXFLAGS += -Wno-narrowing -Wno-unused-variable -Wno-c++11-compat
-HOST_EXTRACXXFLAGS += -Wno-format-diag
-
-$(obj)/randomize_layout_plugin.o: $(objtree)/$(obj)/randomize_layout_seed.h
+$(obj)/randomize_layout_plugin.so: $(objtree)/$(obj)/randomize_layout_seed.h
 quiet_cmd_create_randomize_layout_seed = GENSEED $@
 cmd_create_randomize_layout_seed = \
   $(CONFIG_SHELL) $(srctree)/$(src)/gen-random-seed.sh $@ $(objtree)/include/generated/randomize_layout_hash.h
 $(objtree)/$(obj)/randomize_layout_seed.h: FORCE
 	$(call if_changed,create_randomize_layout_seed)
-targets = randomize_layout_seed.h randomize_layout_hash.h
+targets += randomize_layout_seed.h randomize_layout_hash.h
+
+# Build rules for plugins
+#
+# No extra code is needed for single-file plugins.
+# For multi-file plugins, use *-objs syntax to list the objects.
+#
+# If the plugin foo.so is compiled from foo.c and foo2.c, you can do:
+#
+# foo-objs := foo.o foo2.o
+
+always-y += $(GCC_PLUGIN)
 
-hostcxxlibs-y := $(GCC_PLUGIN)
-always-y := $(hostcxxlibs-y)
+GCC_PLUGINS_DIR = $(shell $(CC) -print-file-name=plugin)
 
-$(foreach p,$(hostcxxlibs-y:%.so=%),$(eval $(p)-objs := $(p).o))
+plugin_cxxflags	= -Wp,-MMD,$(depfile) $(KBUILD_HOSTCXXFLAGS) -fPIC \
+		   -I $(GCC_PLUGINS_DIR)/include -I $(obj) -std=gnu++98 \
+		   -fno-rtti -fno-exceptions -fasynchronous-unwind-tables \
+		   -ggdb -Wno-narrowing -Wno-unused-variable -Wno-c++11-compat \
+		   -Wno-format-diag
 
+plugin_ldflags	= -shared
+
+plugin-single	:= $(foreach m, $(GCC_PLUGIN), $(if $($(m:%.so=%-objs)),,$(m)))
+plugin-multi	:= $(filter-out $(plugin-single), $(GCC_PLUGIN))
+plugin-objs	:= $(sort $(foreach m, $(plugin-multi), $($(m:%.so=%-objs))))
+
+targets += $(plugin-single) $(plugin-multi) $(plugin-objs)
 clean-files += *.so
+
+plugin-single	:= $(addprefix $(obj)/, $(plugin-single))
+plugin-multi	:= $(addprefix $(obj)/, $(plugin-multi))
+plugin-objs	:= $(addprefix $(obj)/, $(plugin-objs))
+
+quiet_cmd_plugin_cxx_so_c = HOSTCXX $@
+      cmd_plugin_cxx_so_c = $(HOSTCXX) $(plugin_cxxflags) $(plugin_ldflags) -o $@ $<
+
+$(plugin-single): $(obj)/%.so: $(src)/%.c FORCE
+	$(call if_changed_dep,plugin_cxx_so_c)
+
+quiet_cmd_plugin_ld_so_o = HOSTLD  $@
+      cmd_plugin_ld_so_o = $(HOSTCXX) $(plugin_ldflags) -o $@ \
+			   $(addprefix $(obj)/, $($(target-stem)-objs))
+
+$(plugin-multi): FORCE
+	$(call if_changed,plugin_ld_so_o)
+$(foreach m, $(notdir $(plugin-multi)), $(eval $(obj)/$m: $(addprefix $(obj)/, $($(m:%.so=%-objs)))))
+
+quiet_cmd_plugin_cxx_o_c = HOSTCXX $@
+      cmd_plugin_cxx_o_c = $(HOSTCXX) $(plugin_cxxflags) -c -o $@ $<
+
+$(plugin-objs): $(obj)/%.o: $(src)/%.c FORCE
+	$(call if_changed_dep,plugin_cxx_o_c)