contrib/plugins: use an independent makefile

The initial reason to write this patch was to remove the last use of
CONFIG_DEBUG_TCG from the makefiles; the flags to use to build TCG
plugins are unrelated to --enable-debug-tcg, and instead they should
be the same as those used to build emulators (the plugins are not build
via meson for demonstration reasons only).

However, since contrib/plugins/Makefile is also the last case of doing
a compilation job using config-host.mak, go a step further and make it
use a completely separate configuration file, removing all references
to compilers from the toplevel config-host.mak.  Clean up references to
empty variables, and use .SECONDARY so that intermediate object files
are not deleted.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -245,7 +245,7 @@ for opt do
   esac
 done
 
-
+default_cflags='-O2 -g'
 git_submodules_action="update"
 git="git"
 docs="auto"
@@ -732,6 +732,7 @@ for opt do
       meson_option_parse --enable-debug-graph-lock ""
       meson_option_parse --enable-debug-mutex ""
       meson_option_add -Doptimization=0
+      default_cflags='-O0 -g'
   ;;
   --disable-tcg) tcg="disabled"
                  plugins="no"
@@ -1731,8 +1732,6 @@ echo "PYTHON=$python" >> $config_host_mak
 echo "GENISOIMAGE=$genisoimage" >> $config_host_mak
 echo "MESON=$meson" >> $config_host_mak
 echo "NINJA=$ninja" >> $config_host_mak
-echo "PKG_CONFIG=${pkg_config}" >> $config_host_mak
-echo "CC=$cc" >> $config_host_mak
 echo "EXESUF=$EXESUF" >> $config_host_mak
 
 # use included Linux headers for KVM architectures
@@ -1757,6 +1756,16 @@ if test "$ccache_cpp2" = "yes"; then
   echo "export CCACHE_CPP2=y" >> $config_host_mak
 fi
 
+# contrib/plugins configuration
+echo "# Automatically generated by configure - do not modify" > contrib/plugins/$config_host_mak
+echo "SRC_PATH=$source_path/contrib/plugins" >> contrib/plugins/$config_host_mak
+echo "PKG_CONFIG=${pkg_config}" >> contrib/plugins/$config_host_mak
+echo "CC=$cc $CPU_CFLAGS" >> contrib/plugins/$config_host_mak
+echo "CFLAGS=${CFLAGS-$default_cflags} $EXTRA_CFLAGS" >> contrib/plugins/$config_host_mak
+if test "$targetos" = darwin; then
+  echo "CONFIG_DARWIN=y" >> contrib/plugins/$config_host_mak
+fi
+
 # tests/tcg configuration
 (config_host_mak=tests/tcg/config-host.mak
 mkdir -p tests/tcg

contrib/plugins/Makefile

@@ -6,11 +6,11 @@
 # programs that the main configure has already done for us.
 #
 
-BUILD_DIR := $(CURDIR)/../..
+include config-host.mak
 
-include $(BUILD_DIR)/config-host.mak
+TOP_SRC_PATH = $(SRC_PATH)/../..
 
-VPATH += $(SRC_PATH)/contrib/plugins
+VPATH += $(SRC_PATH)
 
 NAMES :=
 NAMES += execlog
@@ -26,15 +26,14 @@ SONAMES := $(addsuffix .so,$(addprefix lib,$(NAMES)))
 
 # The main QEMU uses Glib extensively so it's perfectly fine to use it
 # in plugins (which many example do).
-CFLAGS := $(shell $(PKG_CONFIG) --cflags glib-2.0)
-CFLAGS += -fPIC -Wall
-CFLAGS += $(if $(CONFIG_DEBUG_TCG), -ggdb -O0)
-CFLAGS += -I$(SRC_PATH)/include/qemu
+PLUGIN_CFLAGS := $(shell $(PKG_CONFIG) --cflags glib-2.0)
+PLUGIN_CFLAGS += -fPIC -Wall
+PLUGIN_CFLAGS += -I$(TOP_SRC_PATH)/include/qemu
 
 all: $(SONAMES)
 
 %.o: %.c
-	$(CC) $(CFLAGS) -c -o $@ $<
+	$(CC) $(CFLAGS) $(PLUGIN_CFLAGS) -c -o $@ $<
 
 lib%.so: %.o
 ifeq ($(CONFIG_DARWIN),y)
@@ -48,3 +47,4 @@ clean:
 	rm -Rf .libs
 
 .PHONY: all clean
+.SECONDARY: