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From:   Eric Curtin <ecurtin@redhat.com>
Date:   Wed, 11 Jan 2023 16:16:05 +0000
Message-ID: <CAOgh=FxuUA_-rcp-p-R-WV6zYhywztNeXOfpuO5rFo=UJ5xVJA@mail.gmail.com>
Subject: Re: [PATCH v3] scripts: Exclude Rust CUs with pahole
To:     Neal Gompa <neal@gompa.dev>
Cc:     Martin Rodriguez Reboredo <yakoyoku@gmail.com>,
        linux-kernel@vger.kernel.org,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        bpf@vger.kernel.org, rust-for-linux@vger.kernel.org,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Jiri Olsa <jolsa@kernel.org>, Yonghong Song <yhs@fb.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
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On Wed, 11 Jan 2023 at 15:34, Neal Gompa <neal@gompa.dev> wrote:
>
> On Wed, Jan 11, 2023 at 10:21 AM Martin Rodriguez Reboredo
> <yakoyoku@gmail.com> wrote:
> >
> > Version 1.24 of pahole has the capability to exclude compilation units
> > (CUs) of specific languages [1] [2]. Rust, as of writing, is not
> > currently supported by pahole and if it's used with a build that has
> > BTF debugging enabled it results in malformed kernel and module
> > binaries [3]. So it's better for pahole to exclude Rust CUs until
> > support for it arrives.
> >
> > Link: https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?id=
=3D49358dfe2aaae4e90b072332c3e324019826783f [1]
> > Link: https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?id=
=3D8ee363790b7437283c53090a85a9fec2f0b0fbc4 [2]
> > Link: https://github.com/Rust-for-Linux/linux/issues/735 [3]
> >
> > Co-developed-by: Eric Curtin <ecurtin@redhat.com>
> > Signed-off-by: Eric Curtin <ecurtin@redhat.com>
> > Signed-off-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
> > ---
> > V2 -> V3: Enable pahole option upon comparing with version 1.24
> > V1 -> V2: Removed dependency on auto.conf
> >
> >  init/Kconfig            | 2 +-
> >  lib/Kconfig.debug       | 9 +++++++++
> >  scripts/pahole-flags.sh | 4 ++++
> >  3 files changed, 14 insertions(+), 1 deletion(-)
> >
> > diff --git a/init/Kconfig b/init/Kconfig
> > index 694f7c160c9c..360aef8d7292 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -1913,7 +1913,7 @@ config RUST
> >         depends on !MODVERSIONS
> >         depends on !GCC_PLUGINS
> >         depends on !RANDSTRUCT
> > -       depends on !DEBUG_INFO_BTF
> > +       depends on !DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE
>
> Does the order matter here? I'd rather it prefer a fixed pahole and
> disable BTF only if we can't use pahole properly.

The order won't matter.

>
>
> >         select CONSTRUCTORS
> >         help
> >           Enables Rust support in the kernel.
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index ea4c903c9868..d473d491e709 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -364,6 +364,15 @@ config PAHOLE_HAS_BTF_TAG
> >           btf_decl_tag) or not. Currently only clang compiler implement=
s
> >           these attributes, so make the config depend on CC_IS_CLANG.
> >
> > +config PAHOLE_HAS_LANG_EXCLUDE
> > +       def_bool PAHOLE_VERSION >=3D 124
> > +       help
> > +         Support for the --lang_exclude flag which makes pahole exclud=
e
> > +         compilation units from the supplied language. Used in Kbuild =
to
> > +         omit Rust CUs which are not supported in version 1.24 of paho=
le,
> > +         otherwise it would emit malformed kernel and module binaries =
when
> > +         using DEBUG_INFO_BTF_MODULES.
> > +
> >  config DEBUG_INFO_BTF_MODULES
> >         def_bool y
> >         depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF
> > diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> > index 0d99ef17e4a5..1f1f1d397c39 100755
> > --- a/scripts/pahole-flags.sh
> > +++ b/scripts/pahole-flags.sh
> > @@ -19,5 +19,9 @@ fi
> >  if [ "${pahole_ver}" -ge "122" ]; then
> >         extra_paholeopt=3D"${extra_paholeopt} -j"
> >  fi
> > +if [ "${pahole_ver}" -ge "124" ]; then
> > +       # see PAHOLE_HAS_LANG_EXCLUDE
> > +       extra_paholeopt=3D"${extra_paholeopt} --lang_exclude=3Drust"
> > +fi
> >
> >  echo ${extra_paholeopt}
> > --
> > 2.39.0
> >
>
>
> --
> =E7=9C=9F=E5=AE=9F=E3=81=AF=E3=81=84=E3=81=A4=E3=82=82=E4=B8=80=E3=81=A4=
=EF=BC=81/ Always, there's only one truth!
>