[PATCH] KVM: selftest: Add dependency rules in makefile for C source code

[Yu Zhang]

Currently, KVM selftests have to run "make clean && make" to rebuild the
entire test suite each time a header file is modified. Define "-MD" as
an EXTRA_CFLAGS, so we can generate the dependency rules for each target
object, whose prerequisites contains the source file and the included header
files as well. And including those dependency files in KVM selftests' makefile
will release us from such annoyance.

Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
---
 tools/testing/selftests/kvm/Makefile | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index 1750f91dd936..b329e0d1a460 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -180,6 +180,8 @@ TEST_GEN_PROGS += $(TEST_GEN_PROGS_$(ARCH_DIR))
 TEST_GEN_PROGS_EXTENDED += $(TEST_GEN_PROGS_EXTENDED_$(ARCH_DIR))
 LIBKVM += $(LIBKVM_$(ARCH_DIR))
 
+OVERRIDE_TARGETS = 1
+
 # lib.mak defines $(OUTPUT), prepends $(OUTPUT)/ to $(TEST_GEN_PROGS), and most
 # importantly defines, i.e. overwrites, $(CC) (unless `make -e` or `make CC=`,
 # which causes the environment variable to override the makefile).
@@ -198,9 +200,11 @@ CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \
 	-fno-builtin-memcmp -fno-builtin-memcpy -fno-builtin-memset \
 	-fno-stack-protector -fno-PIE -I$(LINUX_TOOL_INCLUDE) \
 	-I$(LINUX_TOOL_ARCH_INCLUDE) -I$(LINUX_HDR_PATH) -Iinclude \
-	-I$(<D) -Iinclude/$(ARCH_DIR) -I ../rseq -I.. $(EXTRA_CFLAGS) \
+	-I$(<D) -Iinclude/$(ARCH_DIR) -I ../rseq -I.. \
 	$(KHDR_INCLUDES)
 
+EXTRA_CFLAGS += -MD
+
 no-pie-option := $(call try-run, echo 'int main(void) { return 0; }' | \
         $(CC) -Werror $(CFLAGS) -no-pie -x c - -o "$$TMP", -no-pie)
 
@@ -218,11 +222,22 @@ LIBKVM_S_OBJ := $(patsubst %.S, $(OUTPUT)/%.o, $(LIBKVM_S))
 LIBKVM_STRING_OBJ := $(patsubst %.c, $(OUTPUT)/%.o, $(LIBKVM_STRING))
 LIBKVM_OBJS = $(LIBKVM_C_OBJ) $(LIBKVM_S_OBJ) $(LIBKVM_STRING_OBJ)
 
-EXTRA_CLEAN += $(LIBKVM_OBJS) cscope.*
+TEST_GEN_OBJ = $(patsubst %, %.o, $(TEST_GEN_PROGS))
+TEST_GEN_OBJ += $(patsubst %, %.o, $(TEST_GEN_PROGS_EXTENDED))
+TEST_DEP_FILES = $(patsubst %.o, %.d, $(TEST_GEN_OBJ))
+TEST_DEP_FILES += $(patsubst %.o, %.d, $(LIBKVM_OBJS))
+-include $(TEST_DEP_FILES)
+
+$(TEST_GEN_PROGS) $(TEST_GEN_PROGS_EXTENDED): %: %.o
+	$(CC) $(CFLAGS) $(CPPFLAGS) $(LDFLAGS) $(TARGET_ARCH) $< $(LIBKVM_OBJS) $(LDLIBS) -o $@
+$(TEST_GEN_OBJ): %.o: %.c
+	$(CC) $(CFLAGS) $(CPPFLAGS) $(EXTRA_CFLAGS) $(TARGET_ARCH) -c $< -o $@
+
+EXTRA_CLEAN += $(LIBKVM_OBJS) $(TEST_DEP_FILES) $(TEST_GEN_OBJ) cscope.*
 
 x := $(shell mkdir -p $(sort $(dir $(LIBKVM_C_OBJ) $(LIBKVM_S_OBJ))))
 $(LIBKVM_C_OBJ): $(OUTPUT)/%.o: %.c
-	$(CC) $(CFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c $< -o $@
+	$(CC) $(CFLAGS) $(CPPFLAGS) $(EXTRA_CFLAGS) $(TARGET_ARCH) -c $< -o $@
 
 $(LIBKVM_S_OBJ): $(OUTPUT)/%.o: %.S
 	$(CC) $(CFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c $< -o $@
-- 
2.25.1