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To: Masahiro Yamada Cc: LKML , Linux Kbuild mailing list , Michal Marek References: From: Florian Fainelli Message-ID: <01279bfe-95a3-dbdb-3785-bd2d92dc4f95@gmail.com> Date: Wed, 6 May 2020 09:03:46 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Firefox/68.0 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/6/2020 7:37 AM, Masahiro Yamada wrote: > On Wed, May 6, 2020 at 1:45 PM Florian Fainelli wrote: >> >> Hi Masahiro, Michal, >> >> While updating our systems from 4.9 to 5.4, we noticed that one of the >> kernel modules that we build, which is done by linking an object that we >> pre-compile out of Kbuild stopped working. >> >> I bisected it down to: >> >> commit 69ea912fda74a673d330d23595385e5b73e3a2b9 (refs/bisect/bad) >> Author: Masahiro Yamada >> Date: Thu Oct 4 13:25:19 2018 +0900 >> >> kbuild: remove unneeded link_multi_deps >> >> Since commit c8589d1e9e01 ("kbuild: handle multi-objs dependency >> appropriately"), $^ really represents all the prerequisite of the >> composite object being built. >> >> Hence, $(filter %.o,$^) contains all the objects to link together, >> which is much simpler than link_multi_deps calculation. >> >> Please note $(filter-out FORCE,$^) does not work here. When a single >> object module is turned into a multi object module, $^ will contain >> header files that were previously included for building the single >> object, and recorded in the .*.cmd file. To filter out such headers, >> $(filter %.o,$^) should be used here. >> >> Signed-off-by: Masahiro Yamada >> >> and the linker now fails with the following: >> >> mkdir -p /home/florian/dev/lkm/.tmp_versions ; rm -f >> /home/florian/dev/lkm/.tmp_versions/* >> >> WARNING: Symbol version dump ./Module.symvers >> is missing; modules will have no dependencies and modversions. >> >> make -f ./scripts/Makefile.build obj=/home/florian/dev/lkm >> (cat /dev/null; echo kernel//home/florian/dev/lkm/hello.ko;) > >> /home/florian/dev/lkm/modules.order >> ld -m elf_x86_64 -z max-page-size=0x200000 -r -o >> /home/florian/dev/lkm/hello.o >> ld: no input files >> make[1]: *** [scripts/Makefile.build:492: /home/florian/dev/lkm/hello.o] >> Error 1 >> make: *** [Makefile:1530: _module_/home/florian/dev/lkm] Error 2 >> >> and here are some steps to reproduce this: >> >> Kbuild: >> obj-m := hello.o >> hello-y := test.o_shipped >> >> test.c can be a simple hello world, and you can compile it using a >> standard Kbuild file first, and then move test.o as test.o_shipped. > > > > Why don't you do like this? > > obj-m := hello.o > hello-y := test.o I tried it in the original environment where it failed, not my contrived test case, and this did not work, as we really need test.o and test.o_shipped to be separate objects, doing what you suggest results in a circular dependency. To me this is a regression, as it used to work and now it does not, thus we should be fixing it, any idea about how we go about it without doing a plain revert? Thank you! -- Florian