On Wed, Feb 14, 2024 at 11:02 PM Marcos Paulo de Souza <mpdesouza@xxxxxxxx> wrote: > > Hello Masahiro and Kbuild ML, > > Recently we added out-of-tree module building on kselftests for the > livepatch selftests. Everything worked as expected, but kernel test > robot complained about it[1]. > > So far, all our tests were being done targeting different options for > kselftests, but we didn't test using the O= option. The interesting > part of it is that this can be easily reproducible with any out-of-tree > module building even on current upstream, like the code below: > > $ uname -r > 6.8.0-rc4+ > $ make > make -C /lib/modules/6.8.0-rc4+/build M=/home/mpdesouza/test-oot > modules > make[1]: Entering directory '/home/mpdesouza/git/linux' > CC [M] /home/mpdesouza/test-oot/patch_1.o > MODPOST /home/mpdesouza/test-oot/Module.symvers > CC [M] /home/mpdesouza/test-oot/patch_1.mod.o > LD [M] /home/mpdesouza/test-oot/patch_1.ko > BTF [M] /home/mpdesouza/test-oot/patch_1.ko > make[1]: Leaving directory '/home/mpdesouza/git/linux' > > But it fails when using O= argument: > $ make O=/tmp/kout > make -C /lib/modules/6.8.0-rc4+/build M=/home/mpdesouza/test-oot > modules > make[1]: Entering directory '/home/mpdesouza/git/linux' > make[2]: Entering directory '/tmp/kout' > /home/mpdesouza/git/linux/Makefile:733: include/config/auto.conf: No > such file or directory > make[2]: *** [/home/mpdesouza/git/linux/Makefile:240: __sub-make] Error > 2 > make[2]: Leaving directory '/tmp/kout' > make[1]: *** [Makefile:240: __sub-make] Error 2 > make[1]: Leaving directory '/home/mpdesouza/git/linux' > make: *** [Makefile:6: all] Error 2 > > As I already described on [2], the O= argument (or KBUILD_OUTPUT) makes > the kernel to jump into the directory specified on the variabled, but > running the Makefile on /lib/modules/6.8.0-rc4+/build. The problem is > thattoplevel Makefile on /lib/modules/.../build includes files using > relative paths. In this case, the makefile tries to find > include/config/auto.conf on /tmp/kout, which obviously doesn't exists. > > Do you think this can be a bug on Kbuild? Should we ignore O= when > building out-of-tree modules? No. O= is not meant for the output directory for external modules. O= is supposed to point to the object tree of the kernel (when the kernel was built in the separate output directory) > Also, as noted[3] by Petr Mladek (CCed here as well), kernel-devel > doesn't include auto.conf, so maybe kernel-devel should be patched as > well? > > Thanks in advance, > Marcos > > [1]: > https://lore.kernel.org/oe-kbuild-all/202401300736.GkSZoSrA-lkp@xxxxxxxxx/ > [2]: > https://lore.kernel.org/oe-kbuild-all/fd027fa958a0bc65285a0c6c42e5921e7d28b0ad.camel@xxxxxxxx/ > [3]: https://lore.kernel.org/oe-kbuild-all/ZbpnBqHUl3pE_3Te@alley/ -- Best Regards Masahiro Yamada
