A question of KVM selftests' makefile

Yu Zhang
2023-01-25T08:54:11Z

Hi all,

Currently, unlike the build system of Linux kernel, KVM selftests will
have to run "make clean && make" to rebuild the entire test suite, once
a header file is modified.

Is it designed like this on purpose, or does anyone wanna change it?

I hacked the makefile by using "-MD" as EXTRA_CFLAGS, so that dependency
rules can be generated for each target object, whose prerequisites contains
the source file and the included header files as well.

However, this change has its own costs. E.g., new ".o" and ".d" files will
occupy more storage. And performance-wise, the benifit could be limited,
because for now, most header files are needed by almost every ".c" files.
But with the evolution of KVM selftests, more ".h" files may be added. Some
of which may be of special usage. E.g., file "include/x86_64/mce.h" is only
used by "x86_64/ucna_injection_test". Having to rebuild the whole test suite
just because one specific header is touched would be annoying.

I am not sure if this change is worthy, or if there's a better solution.
So does anyone have any suggestion?

Below are my current hack in KVM selftest's makefile in case someone is
interested. It can not be optimal and any comment is welcome. Thanks!

B.R.
Yu

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 $@