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authorMasahiro Yamada <masahiroy@kernel.org>2024-11-10 10:34:39 +0900
committerMasahiro Yamada <masahiroy@kernel.org>2024-11-28 08:11:55 +0900
commit8cd07cc6c88cab5cbfe5dd83aacf860a209eb521 (patch)
treed01511c572fcc4dc92fed3e17f08e1af44584ee1 /Makefile
parenta2a45ebee0969b804b1d474a930001a83c954140 (diff)
kbuild: allow to start building external modules in any directory
Unless an explicit O= option is provided, external module builds must start from the kernel directory. This can be achieved by using the -C option: $ make -C /path/to/kernel M=/path/to/external/module This commit allows starting external module builds from any directory, so you can also do the following: $ make -f /path/to/kernel/Makefile M=/path/to/external/module The key difference is that the -C option changes the working directory and parses the Makefile located there, while the -f option only specifies the Makefile to use. As shown in the examples in Documentation/kbuild/modules.rst, external modules usually have a wrapper Makefile that allows you to build them without specifying any make arguments. The Makefile typically contains a rule as follows: KDIR ?= /path/to/kernel default: $(MAKE) -C $(KDIR) M=$(CURDIR) $(MAKECMDGOALS) The log will appear as follows: $ make make -C /path/to/kernel M=/path/to/external/module make[1]: Entering directory '/path/to/kernel' make[2]: Entering directory '/path/to/external/module' CC [M] helloworld.o MODPOST Module.symvers CC [M] helloworld.mod.o CC [M] .module-common.o LD [M] helloworld.ko make[2]: Leaving directory '/path/to/external/module' make[1]: Leaving directory '/path/to/kernel' This changes the working directory twice because the -C option first switches to the kernel directory, and then Kbuild internally recurses back to the external module directory. With this commit, the wrapper Makefile can directly include the kernel Makefile: KDIR ?= /path/to/kernel export KBUILD_EXTMOD := $(realpath $(dir $(lastword $(MAKEFILE_LIST)))) include $(KDIR)/Makefile This avoids unnecessary sub-make invocations: $ make CC [M] helloworld.o MODPOST Module.symvers CC [M] helloworld.mod.o CC [M] .module-common.o LD [M] helloworld.ko Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Diffstat (limited to 'Makefile')
-rw-r--r--Makefile8
1 files changed, 6 insertions, 2 deletions
diff --git a/Makefile b/Makefile
index f0bce5081d53..b77dae5aa03c 100644
--- a/Makefile
+++ b/Makefile
@@ -189,9 +189,13 @@ ifdef KBUILD_EXTMOD
objtree := $(realpath $(KBUILD_OUTPUT))
$(if $(objtree),,$(error specified kernel directory "$(KBUILD_OUTPUT)" does not exist))
else
- objtree := $(CURDIR)
+ objtree := $(abs_srctree)
endif
- output := $(or $(KBUILD_EXTMOD_OUTPUT),$(KBUILD_EXTMOD))
+ # If Make is invoked from the kernel directory (either kernel
+ # source directory or kernel build directory), external modules
+ # are built in $(KBUILD_EXTMOD) for backward compatibility,
+ # otherwise, built in the current directory.
+ output := $(or $(KBUILD_EXTMOD_OUTPUT),$(if $(filter $(CURDIR),$(objtree) $(abs_srctree)),$(KBUILD_EXTMOD)))
# KBUILD_EXTMOD might be a relative path. Remember its absolute path before
# Make changes the working directory.
srcroot := $(realpath $(KBUILD_EXTMOD))