linux-kernel - Re: samples/seccomp/ broken when cross compiling s390, ppc allyesconfig

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Message-ID: <CAGXu5jJZROQMxzxu+Dp3mVMktSg-oTB6pqk7fUyM_6_2oa9c_A@mail.gmail.com>
Date:   Tue, 13 Feb 2018 13:27:30 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Will Drewry <wad@...omium.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        PowerPC <linuxppc-dev@...ts.ozlabs.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: samples/seccomp/ broken when cross compiling s390, ppc allyesconfig

On Tue, Feb 13, 2018 at 2:32 AM, Michal Hocko <mhocko@...nel.org> wrote:
> On Tue 13-02-18 21:16:55, Michael Ellerman wrote:
>> Kees Cook <keescook@...omium.org> writes:
>>
>> > On Mon, Feb 12, 2018 at 7:25 PM, Michael Ellerman <mpe@...erman.id.au> wrote:
>> >> Michal Hocko <mhocko@...nel.org> writes:
>> >>> Hi,
>> >>> my build test machinery chokes on samples/seccomp when cross compiling
>> >>> s390 and ppc64 allyesconfig. This has been the case for quite some
>> >>> time already but I never found time to look at the problem and report
>> >>> it. It seems this is not new issue and similar thing happend for
>> >>> MIPS e9107f88c985 ("samples/seccomp/Makefile: do not build tests if
>> >>> cross-compiling for MIPS").
>> >>>
>> >>> The build logs are attached.
>> >>>
>> >>> What is the best way around this? Should we simply skip compilation on
>> >>> cross compile or is actually anybody relying on that? Or should I simply
>> >>> disable it for s390 and ppc?
>> >>
>> >> The whole thing seems very confused. It's not building for the target,
>> >> it's building for the host, ie. the Makefile sets hostprogs-m and
>> >> HOSTCFLAGS etc.
>> >>
>> >> So it can't possibly work with cross compiling as it's currently
>> >> written.
>> >>
>> >> Either the Makefile needs some serious work to properly support cross
>> >> compiling or it should just be disabled when cross compiling.
>> >
>> > Hrm, yeah, the goal was to entirely disable cross compiling, but I
>> > guess we didn't hit it with a hard enough hammer. :)
>>
>> Do you know why it is written that way? Why doesn't it just try to cross
>> compile like normal code?
>
> No idea, sorry. All I know about this code is that it breaks my build
> testing.

IIRC, one of the problems is with build ordering problems: the kernel
headers used by the samples aren't available when cross compiling.

I'm happy to kill it entirely with Michal's patch, though. Feel free
to carry in your tree!

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

-- 
Kees Cook
Pixel Security