linux-kernel - Re: [PATCH] bpf: Hoise pahole version checks into Kconfig

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Date:   Thu, 4 Feb 2021 08:22:01 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH] bpf: Hoise pahole version checks into Kconfig

On Thu, Jan 14, 2021 at 12:07 AM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> On Wed, Jan 13, 2021 at 02:38:27PM -0800, Andrii Nakryiko wrote:
> > Hm.. Just saw Linus proposing using $(error-if) in Kconfig for an
> > unrelated issue ([0]). If we can make this work, then it would catch
> > such issue early on, yet won't have any downsides of hiding
> > CONFIG_DEBUG_INFO_BTF if pahole is too old. WDYT?
> >
> >   [0] https://lore.kernel.org/lkml/CAHk-=wh-+TMHPTFo1qs-MYyK7tZh-OQovA=pP3=e06aCVp6_kA@mail.gmail.com/
>
> Yes, I think that would be exactly what we want because DEBUG_INFO_BTF
> could cause the build to error if PAHOLE_VERSION is not >= 116. I will
> try to keep an eye on that thread to see how it goes then respin this
> based on anything that comes from it.
>

For BPF/pahole testing (see [1]) with CONFIG_DEBUG_INFO_DWARF5=y I did:

$ git diff
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index b0840d192e95..f15b37143165 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -272,7 +272,7 @@ config DEBUG_INFO_DWARF5
       bool "Generate DWARF Version 5 debuginfo"
       depends on GCC_VERSION >= 50000 || CC_IS_CLANG
       depends on CC_IS_GCC ||
$(success,$(srctree)/scripts/test_dwarf5_support.sh $(CC)
$(CLANG_FLAGS))
-       depends on !DEBUG_INFO_BTF
+       depends on !DEBUG_INFO_BTF || (DEBUG_INFO_BTF && PAHOLE_VERSION >= 120)
       help
         Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc
         5.0+ accepts the -gdwarf-5 flag but only had partial support for some

Thanks again for that patch.

- Sedat -

[1] https://git.kernel.org/pub/scm/devel/pahole/pahole.git/log/?h=tmp.1.20