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author | Masahiro Yamada <masahiroy@kernel.org> | 2024-11-10 10:34:39 +0900 |
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committer | Masahiro Yamada <masahiroy@kernel.org> | 2024-11-28 08:11:55 +0900 |
commit | 8cd07cc6c88cab5cbfe5dd83aacf860a209eb521 (patch) | |
tree | d01511c572fcc4dc92fed3e17f08e1af44584ee1 | |
parent | a2a45ebee0969b804b1d474a930001a83c954140 (diff) | |
download | lwn-8cd07cc6c88cab5cbfe5dd83aacf860a209eb521.tar.gz lwn-8cd07cc6c88cab5cbfe5dd83aacf860a209eb521.zip |
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>
-rw-r--r-- | Documentation/kbuild/modules.rst | 21 | ||||
-rw-r--r-- | Makefile | 8 |
2 files changed, 27 insertions, 2 deletions
diff --git a/Documentation/kbuild/modules.rst b/Documentation/kbuild/modules.rst index a01f3754c7fc..101de236cd0c 100644 --- a/Documentation/kbuild/modules.rst +++ b/Documentation/kbuild/modules.rst @@ -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)) |