The workaround described in the commit message (overwrite 'src') is different from what I know. As I explained to Daniel before, the point is, O= refers to the kernel output directory, and M= specifies a relative path to your downstream module directory. Say, you have a linux source tree and external modules under ~/my-project-src/, and you want to output all build artifacts under ~/my-build-dir/. my-project-src |-- linux \-- my-modules masahiro@zoe:~/my-project-src/my-modules$ tree . |-- Kbuild |-- dir1 | |-- Kbuild | |-- bar.c | `-- dir2 | |-- Kbuild | `-- baz.c `-- foo.c 3 directories, 6 files masahiro@zoe:~/my-project-src/my-modules$ cat Kbuild obj-m += foo.o obj-m += dir1/ masahiro@zoe:~/my-project-src/my-modules$ cat dir1/Kbuild obj-m += bar.o obj-m += dir2/ masahiro@zoe:~/my-project-src/my-modules$ cat dir1/dir2/Kbuild obj-m += baz.o First, build the kernel and external modules in separate output directories. masahiro@zoe:~/my-project-src/linux$ make O=~/my-build-dir/linux defconfig all [ snip ] masahiro@zoe:~/my-project-src/linux$ make O=~/my-build-dir/linux M=../my-modules make[1]: Entering directory '/home/masahiro/my-build-dir/linux' CC [M] ../my-modules/dir1/dir2/baz.o CC [M] ../my-modules/dir1/bar.o CC [M] ../my-modules/foo.o MODPOST ../my-modules/Module.symvers CC [M] ../my-modules/foo.mod.o LD [M] ../my-modules/foo.ko CC [M] ../my-modules/dir1/bar.mod.o LD [M] ../my-modules/dir1/bar.ko CC [M] ../my-modules/dir1/dir2/baz.mod.o LD [M] ../my-modules/dir1/dir2/baz.ko make[1]: Leaving directory '/home/masahiro/my-build-dir/linux' masahiro@zoe:~/my-build-dir/my-modules$ tree . |-- Module.symvers |-- dir1 | |-- bar.ko | |-- bar.mod | |-- bar.mod.c | |-- bar.mod.o | |-- bar.o | |-- dir2 | | |-- baz.ko | | |-- baz.mod | | |-- baz.mod.c | | |-- baz.mod.o | | |-- baz.o | | `-- modules.order | `-- modules.order |-- foo.ko |-- foo.mod |-- foo.mod.c |-- foo.mod.o |-- foo.o `-- modules.order 3 directories, 19 files I saw this before somewhere. I believe it is a well-known workaround that works with recursion. This patch submission is not helpful. Kbuild does not support the external module builds in a separate output directory. Most people know this limitation for a long time. You are not the first person to discover it. Second, anybody can write a patch like yours in several minutes. There already exists a similar (but more correct) patch: https://lore.kernel.org/linux-kbuild/e58cba84c90c40108ac678500f33655e@xxxxxxxxxx/ That one works more correctly than yours, because modpost works with no error, and 'make clean' works too. I am not suggesting to fix scripts/{Makefile.modpost,Makefile.clean}. If such a patch had been acceptable, it would have been accepted many years before. Things are, the decision is postponed until we are confident about a solution. I must avoid a situation where a bad solution is upstreamed as official. That is worse than nothing. And, I am pretty sure that your patch is not the right solution. -- Best Regards Masahiro Yamada
