linux-kernel - Re: [PATCH v4 bpf] kbuild: fix dependencies for DEBUG_INFO

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Date:   Thu, 2 Apr 2020 13:34:32 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Slava Bacherikov <slava@...her09.org>,
        Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Jann Horn <jannh@...gle.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Liu Yiding <liuyd.fnst@...fujitsu.com>, kpsingh@...gle.com
Subject: Re: [PATCH v4 bpf] kbuild: fix dependencies for DEBUG_INFO_BTF

On Thu, Apr 02, 2020 at 12:31:36PM -0700, Andrii Nakryiko wrote:
> On Thu, Apr 2, 2020 at 8:40 AM Slava Bacherikov <slava@...her09.org> wrote:
> >
> >
> >
> > 02.04.2020 18:33, Slava Bacherikov wrote:
> > > +     depends on DEBUG_INFO || COMPILE_TEST
> >
> > Andrii are you fine by this ?
> 
> I think it needs a good comment explaining this weirdness, at least.
> As I said, if there is no DEBUG_INFO, there is not point in doing
> DWARF-to-BTF conversion, even more -- it actually might fail, I
> haven't checked what pahole does in that case. So I'd rather drop
> GCC_PLUGIN_RANDSTRUCT is that's the issue here. DEBUG_INFO_SPLIT and
> DEBUG_INFO_REDUCED look good.

The DEBUG_INFO is separate, AIUI -- it sounds like BTF may entirely
break on a compile with weird DWARF configs.

The GCC_PLUGIN_RANDSTRUCT issue is separate: it doesn't make sense to
run a kernel built with BTF and GCC_PLUGIN_RANDSTRUCT. But they should
have nothing to do with each other with regard to compilation. So, to
keep GCC_PLUGIN_RANDSTRUCT disable for "real" builds but leave it on for
all*config, randconfig, etc, I'd like to keep the || COMPILE_TEST,
otherwise GCC_PLUGIN_RANDSTRUCT won't be part of the many CIs doing
compilation testing.

And FWIW, I'm fine to let GCC_PLUGIN_RANDSTRUCT and BTF build together.
But if they want to be depends-conflicted, I wanted to keep the test
compile trap door.

-- 
Kees Cook