From 30a7729771731971839cc969d2a321e6ea7a144b Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Thu, 23 Apr 2020 23:23:53 +0900 Subject: [PATCH] kbuild: use -MMD instead of -MD to exclude system headers from dependency This omits system headers from the generated header dependency. System headers are not updated unless you upgrade the compiler. Nor do they contain CONFIG options, so fixdep does not need to parse them. Having said that, the effect of this optimization will be quite small because the kernel code generally does not include system headers except . Host programs include a lot of system headers, but there are not so many in the kernel tree. At first, keeping system headers in .*.cmd files might be useful to detect the compiler update, but there is no guarantee that is included from every file. So, I implemented a more reliable way in the previous commit. Signed-off-by: Masahiro Yamada --- scripts/Kbuild.include | 2 +- scripts/Makefile.host | 4 ++-- scripts/Makefile.lib | 8 ++++---- usr/include/Makefile | 2 +- 4 files changed, 8 insertions(+), 8 deletions(-) diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include index 6cabf20ce66a..0c3dc983439b 100644 --- a/scripts/Kbuild.include +++ b/scripts/Kbuild.include @@ -16,7 +16,7 @@ pound := \# dot-target = $(dir $@).$(notdir $@) ### -# The temporary file to save gcc -MD generated dependencies must not +# The temporary file to save gcc -MMD generated dependencies must not # contain a comma depfile = $(subst $(comma),_,$(dot-target).d) diff --git a/scripts/Makefile.host b/scripts/Makefile.host index 2045855d0b75..c8a4a033dc3e 100644 --- a/scripts/Makefile.host +++ b/scripts/Makefile.host @@ -88,8 +88,8 @@ _hostcxx_flags += -I $(objtree)/$(obj) endif endif -hostc_flags = -Wp,-MD,$(depfile) $(_hostc_flags) -hostcxx_flags = -Wp,-MD,$(depfile) $(_hostcxx_flags) +hostc_flags = -Wp,-MMD,$(depfile) $(_hostc_flags) +hostcxx_flags = -Wp,-MMD,$(depfile) $(_hostcxx_flags) ##### # Compile programs on the host diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib index 4b799737722c..12f6a331a8f3 100644 --- a/scripts/Makefile.lib +++ b/scripts/Makefile.lib @@ -171,22 +171,22 @@ modkern_aflags = $(if $(part-of-module), \ $(KBUILD_AFLAGS_MODULE) $(AFLAGS_MODULE), \ $(KBUILD_AFLAGS_KERNEL) $(AFLAGS_KERNEL)) -c_flags = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE) \ +c_flags = -Wp,-MMD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE) \ -include $(srctree)/include/linux/compiler_types.h \ $(_c_flags) $(modkern_cflags) \ $(basename_flags) $(modname_flags) -a_flags = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE) \ +a_flags = -Wp,-MMD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE) \ $(_a_flags) $(modkern_aflags) -cpp_flags = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE) \ +cpp_flags = -Wp,-MMD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE) \ $(_cpp_flags) ld_flags = $(KBUILD_LDFLAGS) $(ldflags-y) $(LDFLAGS_$(@F)) DTC_INCLUDE := $(srctree)/scripts/dtc/include-prefixes -dtc_cpp_flags = -Wp,-MD,$(depfile).pre.tmp -nostdinc \ +dtc_cpp_flags = -Wp,-MMD,$(depfile).pre.tmp -nostdinc \ $(addprefix -I,$(DTC_INCLUDE)) \ -undef -D__DTS__ diff --git a/usr/include/Makefile b/usr/include/Makefile index b568a95d1f62..5a7ee3e5ed86 100644 --- a/usr/include/Makefile +++ b/usr/include/Makefile @@ -8,7 +8,7 @@ # We cannot go as far as adding -Wpedantic since it emits too many warnings. UAPI_CFLAGS := -std=c90 -Wall -Werror=implicit-function-declaration -override c_flags = $(UAPI_CFLAGS) -Wp,-MD,$(depfile) -I$(objtree)/usr/include +override c_flags = $(UAPI_CFLAGS) -Wp,-MMD,$(depfile) -I$(objtree)/usr/include # The following are excluded for now because they fail to build. #