@@ -59,6 +59,12 @@ Command Syntax
$ make -C /lib/modules/`uname -r`/build M=$PWD modules_install
+ Starting from Linux 6.13, you can use the -f option instead of -C. This
+ will avoid unnecessary change of the working directory. The external
+ module will be output to the directory where you invoke make.
+
+ $ make -f /lib/modules/`uname -r`/build/Makefile M=$PWD
+
Options
-------
@@ -221,6 +227,21 @@ Separate Kbuild File and Makefile
consisting of several hundred lines, and here it really pays
off to separate the kbuild part from the rest.
+ Linux 6.13 and later support another way. The external module Makefile
+ can include the kernel Makefile directly, rather than invoking sub Make.
+
+ Example 3::
+
+ --> filename: Kbuild
+ obj-m := 8123.o
+ 8123-y := 8123_if.o 8123_pci.o
+
+ --> filename: Makefile
+ KDIR ?= /lib/modules/$(shell uname -r)/build
+ export KBUILD_EXTMOD := $(realpath $(dir $(lastword $(MAKEFILE_LIST))))
+ include $(KDIR)/Makefile
+
+
Building Multiple Modules
-------------------------
@@ -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))
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> --- Changes in v2: - Fix typos in the commit description (s/exernal/external/) - Fix `uname -r` to $(shell uname -r) in Example 3 Documentation/kbuild/modules.rst | 21 +++++++++++++++++++++ Makefile | 8 ++++++-- 2 files changed, 27 insertions(+), 2 deletions(-)