On 5/6/2020 7:37 AM, Masahiro Yamada wrote:
> On Wed, May 6, 2020 at 1:45 PM Florian Fainelli <f.fainelli@xxxxxxxxx> 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 <yamada.masahiro@xxxxxxxxxxxxx>
>> 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 <yamada.masahiro@xxxxxxxxxxxxx>
>>
>> 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
