Re: [PATCH] Documentation/kbuild/makefiles.txt: Improve description of lib-* targets

[Randy Dunlap <rdunlap@infradead.org>]

On 05/10/2014 10:02 PM, George Spelvin wrote:
> I had to ask on the mailing list, so save developers the bother of
> answering the question again.  (Wanna-be kernel developers might also
> be helped, but who cares about them?)
> 
> Signed-off-by: George Spelvin <linux@horizon.com>
> ---
> As with most documentation patches, this is also an exercise in eliciting
> corrections by proposing a wrong answer which will be jumped on.

Hi Michal,

Any comments on this patch?

Thanks.

> 
>  Documentation/kbuild/makefiles.txt | 23 +++++++++++++++++++++--
>  1 file changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
> index d567a7cc55..f6cc266163 100644
> --- a/Documentation/kbuild/makefiles.txt
> +++ b/Documentation/kbuild/makefiles.txt
> @@ -237,10 +237,29 @@ more details, with real examples.
>  	be included in a library, lib.a.
>  	All objects listed with lib-y are combined in a single
>  	library for that directory.
> +
> +	The entire kernel is then linked against these libraries,
> +	so the linker will include the code in the final kernel only
> +	if it is referenced somewhere.  Thus, lib-* goals may be
> +	designed with false positives.
> +
>  	Objects that are listed in obj-y and additionally listed in
>  	lib-y will not be included in the library, since they will
>  	be accessible anyway.
> -	For consistency, objects listed in lib-m will be included in lib.a.
> +
> +	For consistency, objects listed in lib-m will be included
> +	in lib.a, but this will probably not do what you want.	If a
> +	function in lib.a is referenced only from a module, and not from
> +	the main kernel image, the linker will not incorporate it into
> +	the kernel image and later attempts to load the module will fail.
> +
> +	One solution to this issue are to declare the object boolean
> +	and link it into the kernel with obj-y if it's depended on by
> +	a module.  The object's code will be included in the main kernel
> +	but unused until the module is loaded.
> +
> +	The other is to make the object a module itself, and use an
> +	obj-m goal.  Many helper modules in lib are used this way.
>  
>  	Note that the same kbuild makefile may list files to be built-in
>  	and to be part of a library. Therefore the same directory
> @@ -252,7 +271,7 @@ more details, with real examples.
>  
>  	This will create a library lib.a based on delay.o. For kbuild to
>  	actually recognize that there is a lib.a being built, the directory
> -	shall be listed in libs-y.
> +	must be listed in libs-y in its parent makefile.
>  	See also "6.4 List directories to visit when descending".
>  
>  	Use of lib-y is normally restricted to lib/ and arch/*/lib.
> 


-- 
~Randy