path: root/scripts
diff options
authorMasahiro Yamada <>2020-04-23 23:23:53 +0900
committerMasahiro Yamada <>2020-05-12 13:28:33 +0900
commit30a7729771731971839cc969d2a321e6ea7a144b (patch)
tree5ecc32acc767d02fde56084c435073be35ab3486 /scripts
parent8b59cd81dc5e724eaea283fa6006985891c7bff4 (diff)
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 <stdarg.h>. 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 <stdarg.h> is included from every file. So, I implemented a more reliable way in the previous commit. Signed-off-by: Masahiro Yamada <>
Diffstat (limited to 'scripts')
3 files changed, 7 insertions, 7 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/ b/scripts/
index 2045855d0b75..c8a4a033dc3e 100644
--- a/scripts/
+++ b/scripts/
@@ -88,8 +88,8 @@ _hostcxx_flags += -I $(objtree)/$(obj)
-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 $(part-of-module), \
-c_flags = -Wp,-MD,$(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) \
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__