linux-kernel - Re: [PATCH] KVM: selftest: Add dependency rules in makefile for C source code

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Date:   Fri, 17 Mar 2023 17:09:53 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Yu Zhang <yu.c.zhang@...ux.intel.com>, pbonzini@...hat.com,
        shuah@...nel.org, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: selftest: Add dependency rules in makefile for C
 source code

> Do we actually need to omit -MD here?  IIUC, it just means that the .d file will
> get redundantly generated when building the final executable.  I would much prefer
> to build everything with the same options unless there's a good reason not to,
> e.g. this patch doesn't feed -MD into the LIBKVM_STRING_OBJ target, which seems
> wrong.

No, we don't. I added "-MD" in EXTRA_CFLAGS, so that only .o files would
be impacted when generating dependency files. But it is unnecessary.

As to the LIBKVM_STRING_OBJ target, it is my negligence. :)

I tried your suggested fix, and it works fine. Will send out v2(based on
selftests branch of github.com/kvm-x86/linux). Thanks!

B.R.
Yu
> 
> I.e. why not simply
> 
> ---
>  tools/testing/selftests/kvm/Makefile | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index 152c1a988e42..faaf65aa7621 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -182,6 +182,8 @@ 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).
> @@ -196,7 +198,7 @@ else
>  LINUX_TOOL_ARCH_INCLUDE = $(top_srcdir)/tools/arch/$(ARCH)/include
>  endif
>  CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \
> -	-Wno-gnu-variable-sized-type-not-at-end \
> +	-Wno-gnu-variable-sized-type-not-at-end -MD \
>  	-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 \
> @@ -223,7 +225,18 @@ 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) $(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
> 
> base-commit: 95b9779c1758f03cf494e8550d6249a40089ed1c
> -- 
>