On Sat, Jan 23, 2021 at 4:27 AM Elliot Berman [off-list ref] wrote:

This series was developed after discussion in https://lkml.org/lkml/2021/1/19/850

The motivation for this series is an out-of-tree module which contains a large
number of source files. This causes Kbuild to exceed the maximum command line
argument length when linking the files. Proposal here permits composite objects
to contain other composite objects. This allows the driver to split linking into
several steps and avoid the maximum command line length error.

External modules often get the cold shoulder.

For example,
https://lore.kernel.org/patchwork/patch/1175556/#1372233


This problem has not been observed in the upstream tree.

I do not see a good reason to complicate the build
infrastructure for some external modules.

Kbuild composite objects only supports one level of composite objects.
That is, a composite object may only be composed of real compilable
source files.

As a simple example, the following Kbuild description is now supported:

bar-a-y := a/bar0.o a/bar1.o
bar-b-y := b/bar2.o b/bar3.o

foo-objs := bar-a.o bar-b.o

obj-m += foo.o

Add such support by recursively searching for composite objects and
listing them in $(multi-used-*) and $(real-obj-*).

Elliot Berman (2):
  Kbuild: Make composite object searching more generic
  Kbuild: Support nested composite objects

 scripts/Makefile.lib | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

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Best Regards
Masahiro Yamada