Masahiro Yamada <masahi...@kernel.org> writes:
> On Thu, Dec 24, 2020 at 2:12 AM Masahiro Yamada <masahi...@kernel.org> wrote:
>>
>> vgettimeofday.o is unnecessarily rebuilt. Adding it to 'targets' is not
>> enough to fix the issue. Kbuild is correctly rebuilding it because the
>> command line is changed.
>>
>> PowerPC builds each vdso directory twice; first in vdso_prepare to
>> generate vdso{32,64}-offsets.h, second as part of the ordinary build
>> process to embed vdso{32,64}.so.dbg into the kernel.
>>
>> The problem shows up when CONFIG_PPC_WERROR=y due to the following line
>> in arch/powerpc/Kbuild:
>>
>> subdir-ccflags-$(CONFIG_PPC_WERROR) := -Werror
>>
>> In the preparation stage, Kbuild directly visits the vdso directories,
>> hence it does not inherit subdir-ccflags-y. In the second descend,
>> Kbuild adds -Werror, which results in the command line flipping
>> with/without -Werror.
>>
>> It implies a potential danger; if a more critical flag that would impact
>> the resulted vdso, the offsets recorded in the headers might be different
>> from real offsets in the embedded vdso images.
>>
>> Removing the unneeded second descend solves the problem.
>>
>> Link: https://lore.kernel.org/linuxppc-dev/87tuslxhry....@mpe.ellerman.id.au/
>> Reported-by: Michael Ellerman <m...@ellerman.id.au>
>> Signed-off-by: Masahiro Yamada <masahi...@kernel.org>
>> ---
>
>
> Michael, please take a look at this.
>
> The unneeded rebuild problem is still remaining.
Sorry missed those.
I guess I'll pick these up as fixes for v5.10.
cheers
