Documentation/kbuild/modules.rst

2 Building External Modules
10 	=== 2 How to Build External Modules
19 	   --- 3.4 Building Multiple Modules
29 	   --- 6.1 Symbols From the Kernel (vmlinux + modules)
30 	   --- 6.2 Symbols and External Modules
40 "kbuild" is the build system used by the Linux kernel. Modules must use
42 to pick up the right flags to "gcc." Functionality for building modules
44 either is similar, and all modules are initially developed and built
48 in building out-of-tree (or "external") modules. The author of an
55 2. How to Build External Modules
58 To build external modules, you must have a prebuilt kernel available
60 Also, the kernel must have been built with modules enabled. If you are
67 building external modules.
85 		$ make -C /lib/modules/`uname -r`/build M=$PWD
90 		$ make -C /lib/modules/`uname -r`/build M=$PWD modules_install
125 	modules
126 		The default target for external modules. It has the
132 		/lib/modules/<kernel_release>/extra/, but a prefix may
143 		List the available targets for external modules.
150 	external modules.
210 		KDIR ?= /lib/modules/`uname -r`/build
244 		KDIR ?= /lib/modules/`uname -r`/build
254 	each file; however, some external modules use makefiles
273 		KDIR ?= /lib/modules/`uname -r`/build
292 	Some external modules need to include an object file as a blob.
309 3.4 Building Multiple Modules
312 	kbuild supports building multiple modules with a single build
313 	file. For example, if you wanted to build two modules, foo.ko
356 	External modules tend to place header files in a separate
417 	External modules may export headers to userspace in a similar
429 Modules which are included in the kernel are installed in the
432 	/lib/modules/$(KERNELRELEASE)/kernel/
434 And external modules are installed in:
436 	/lib/modules/$(KERNELRELEASE)/extra/
446 		=> Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel/
451 	and out-of-tree modules.
456 	External modules are by default installed to a directory under
457 	/lib/modules/$(KERNELRELEASE)/extra/, but you may wish to
458 	locate modules for a specific functionality in a separate
464 		=> Install dir: /lib/modules/$(KERNELRELEASE)/gandalf/
480 6.1 Symbols From the Kernel (vmlinux + modules)
485 	the kernel and compiled modules. For each symbol, the
502 	1) It lists all exported symbols from vmlinux and all modules.
505 6.2 Symbols and External Modules
527 		If you have two modules, foo.ko and bar.ko, where
529 		common top-level kbuild file so both modules are
545 		will then do the expected and compile both modules with
562 	Modules often need to check for certain `CONFIG_` options to
573 	External modules have traditionally used "grep" to check for
575 	broken. As introduced before, external modules should use
577 	in-tree modules when testing for `CONFIG_` definitions.