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How to create an external module in kbuild?
Some external modules need to include an object file as a blob. kbuild has support for this, but requires the blob file to be named _shipped. When the kbuild rules kick in, a copy of _shipped is created with _shipped stripped off, giving us . This shortened filename can be used in the assignment to the module.
Which is the output directory in kbuild _ extmod?
Set the directory to look for the kernel source when building external modules. Setting “M=…” takes precedence over KBUILD_EXTMOD. Specify the output directory when building the kernel. The output directory can also be specified using “O=…”. Setting “O=…” takes precedence over KBUILD_OUTPUT.
Is it possible to build an external module with no arguments?
An external module always includes a wrapper makefile that supports building the module using “make” with no arguments. This target is not used by kbuild; it is only for convenience. Additional functionality, such as test targets, can be included but should be filtered out from kbuild due to possible name clashes.
Where are external modules located in the kernel?
External modules tend to place header files in a separate include/ directory where their source is located, although this is not the usual kernel style. To inform kbuild of the directory, use either ccflags-y or CFLAGS_ .o.
What does kbuild do in the Linux kernel?
In newer versions of the kernel, kbuild will first look for a file named “Kbuild,” and only if that is not found, will it then look for a makefile. Utilizing a “Kbuild” file allows us to split up the makefile from example 1 into two files:
Why is kbuild included in the Makefile?
Here the “Kbuild” file is included from the makefile. This allows an older version of kbuild, which only knows of makefiles, to be used when the “make” and kbuild parts are split into separate files.
Where to install user space headers in kbuild?
INSTALL_HDR_PATH specifies where to install user space headers when executing “make headers_*”. $ (objtree) is the directory where output files are saved. The output directory is often set using “O=…” on the commandline. The value can be overridden in which case the default value is ignored.