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@xxxxxxxxxxx> --- As with most documentation patches, this is also an exercise in eliciting corrections by proposing a wrong answer which will be jumped on. 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. -- 1.9.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
