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Subject[PATCH 2/5] kbuild: define KBUILD_MODNAME even if multiple modules share objects
Currently, KBUILD_MODNAME is defined only when $(modname) contains
just one word. If an object is shared among multiple modules,
undefined KBUILD_MODNAME could cause a build error. For example,
if CONFIG_DYNAMIC_DEBUG is enabled, any call of printk() populates
.modname, then fails to build due to undefined KBUILD_MODNAME.

Take the following code as an example:

obj-m += foo.o
obj-m += bar.o
foo-objs := foo-bar-common.o foo-main.o
bar-objs := foo-bar-common.o bar-main.o

In this case, there is room for argument what to define for
KBUILD_MODNAME when foo-bar-common.o is being compiled.
"foo", "bar", or what else?

One idea is to define colon-separated modules that share the object,
in this case, "bar:foo" (modules are sorted alphabetically by
$(sort ...).

Signed-off-by: Masahiro Yamada <>

scripts/Makefile.lib | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index a7e315f..a1fbd6a 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -92,8 +92,7 @@ subdir-ym := $(addprefix $(obj)/,$(subdir-ym))
# differ in different configs.
name-fix = $(squote)$(quote)$(subst $(comma),_,$(subst -,_,$1))$(quote)$(squote)
basename_flags = -DKBUILD_BASENAME=$(call name-fix,$(basetarget))
-modname_flags = $(if $(filter 1,$(words $(modname))),\
- -DKBUILD_MODNAME=$(call name-fix,$(modname)))
+modname_flags = -DKBUILD_MODNAME=$(call name-fix,$(modname))

orig_c_flags = $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) \
$(ccflags-y) $(CFLAGS_$(basetarget).o)
@@ -174,8 +173,10 @@ dtc_cpp_flags = -Wp,-MD,$(depfile).pre.tmp -nostdinc \
-undef -D__DTS__

# Finds the multi-part object the current object will be linked into
-modname-multi = $(sort $(foreach m,$(multi-used),\
- $(if $(filter $*.o, $($(m:.o=-objs)) $($(m:.o=-y))),$(m:.o=))))
+# If the object belongs to two or more multi-part objects, all of them are
+# concatenated with a colon separator.
+modname-multi = $(subst $(space),:,$(sort $(foreach m,$(multi-used),\
+ $(if $(filter $*.o, $($(m:.o=-objs)) $($(m:.o=-y))),$(m:.o=)))))

# Useful for describing the dependency of composite objects
# Usage:
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