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, 2 insertions, 28 deletions

diff --git a/scripts/Makefile.host b/scripts/Makefile.host
index c8a4a033dc3e..687ca3f309e9 100644
--- a/scripts/Makefile.host
+++ b/scripts/Makefile.host
@@ -39,7 +39,6 @@ $(obj)/%.tab.c $(obj)/%.tab.h: $(src)/%.y FORCE
 # They are linked as C++ code to the executable qconf
 
 __hostprogs := $(sort $(hostprogs))
-host-cxxshlib := $(sort $(hostcxxlibs-y) $(hostcxxlibs-m))
 
 # C code
 # Executables compiled from a single .c file
@@ -61,16 +60,11 @@ host-cxxmulti	:= $(foreach m,$(__hostprogs),$(if $($(m)-cxxobjs),$(m)))
 # C++ Object (.o) files compiled from .cc files
 host-cxxobjs	:= $(sort $(foreach m,$(host-cxxmulti),$($(m)-cxxobjs)))
 
-# Object (.o) files used by the shared libaries
-host-cxxshobjs	:= $(sort $(foreach m,$(host-cxxshlib),$($(m:.so=-objs))))
-
 host-csingle	:= $(addprefix $(obj)/,$(host-csingle))
 host-cmulti	:= $(addprefix $(obj)/,$(host-cmulti))
 host-cobjs	:= $(addprefix $(obj)/,$(host-cobjs))
 host-cxxmulti	:= $(addprefix $(obj)/,$(host-cxxmulti))
 host-cxxobjs	:= $(addprefix $(obj)/,$(host-cxxobjs))
-host-cxxshlib	:= $(addprefix $(obj)/,$(host-cxxshlib))
-host-cxxshobjs	:= $(addprefix $(obj)/,$(host-cxxshobjs))
 
 #####
 # Handle options to gcc. Support building with separate output directory
@@ -136,25 +130,5 @@ quiet_cmd_host-cxxobjs	= HOSTCXX $@
 $(host-cxxobjs): $(obj)/%.o: $(src)/%.cc FORCE
 	$(call if_changed_dep,host-cxxobjs)
 
-# Compile .c file, create position independent .o file
-# Note that plugin capable gcc versions can be either C or C++ based
-# therefore plugin source files have to be compilable in both C and C++ mode.
-# This is why a C++ compiler is invoked on a .c file.
-# host-cxxshobjs -> .o
-quiet_cmd_host-cxxshobjs	= HOSTCXX -fPIC $@
-      cmd_host-cxxshobjs	= $(HOSTCXX) $(hostcxx_flags) -fPIC -c -o $@ $<
-$(host-cxxshobjs): $(obj)/%.o: $(src)/%.c FORCE
-	$(call if_changed_dep,host-cxxshobjs)
-
-# Link a shared library, based on position independent .o files
-# *.o -> .so shared library (host-cxxshlib)
-quiet_cmd_host-cxxshlib	= HOSTLLD -shared $@
-      cmd_host-cxxshlib	= $(HOSTCXX) $(KBUILD_HOSTLDFLAGS) -shared -o $@ \
-			  $(addprefix $(obj)/, $($(target-stem)-objs)) \
-			  $(KBUILD_HOSTLDLIBS) $(HOSTLDLIBS_$(target-stem).so)
-$(host-cxxshlib): FORCE
-	$(call if_changed,host-cxxshlib)
-$(call multi_depend, $(host-cxxshlib), .so, -objs)
-
-targets += $(host-csingle)  $(host-cmulti) $(host-cobjs)\
-	   $(host-cxxmulti) $(host-cxxobjs) $(host-cxxshlib) $(host-cxxshobjs)
+targets += $(host-csingle) $(host-cmulti) $(host-cobjs) \
+	   $(host-cxxmulti) $(host-cxxobjs)