linux-kernel - Re: [PATCH v3] scripts: Exclude Rust CUs with pahole

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Message-ID: <CAOgh=FxQQ6o6+JS5DaXu=SPyYssXTXgt4+njvnZ5b0msKj5c_w@mail.gmail.com>
Date:   Wed, 11 Jan 2023 15:22:29 +0000
From:   Eric Curtin <ecurtin@...hat.com>
To:     Martin Rodriguez Reboredo <yakoyoku@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Neal Gompa <neal@...pa.dev>, bpf@...r.kernel.org,
        rust-for-linux@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>, Yonghong Song <yhs@...com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Subject: Re: [PATCH v3] scripts: Exclude Rust CUs with pahole

On Wed, 11 Jan 2023 at 15:21, Martin Rodriguez Reboredo
<yakoyoku@...il.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=49358dfe2aaae4e90b072332c3e324019826783f [1]
> Link: https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?id=8ee363790b7437283c53090a85a9fec2f0b0fbc4 [2]
> Link: https://github.com/Rust-for-Linux/linux/issues/735 [3]
>
> Co-developed-by: Eric Curtin <ecurtin@...hat.com>
> Signed-off-by: Eric Curtin <ecurtin@...hat.com>
> Signed-off-by: Martin Rodriguez Reboredo <yakoyoku@...il.com>

I think this should be able to cover all the quirky build techniques.

Tested-by: Eric Curtin <ecurtin@...hat.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
>         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 implements
>           these attributes, so make the config depend on CC_IS_CLANG.
>
> +config PAHOLE_HAS_LANG_EXCLUDE
> +       def_bool PAHOLE_VERSION >= 124
> +       help
> +         Support for the --lang_exclude flag which makes pahole exclude
> +         compilation units from the supplied language. Used in Kbuild to
> +         omit Rust CUs which are not supported in version 1.24 of pahole,
> +         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 [ "${pahole_ver}" -ge "122" ]; then
>         extra_paholeopt="${extra_paholeopt} -j"
>  fi
> +if [ "${pahole_ver}" -ge "124" ]; then
> +       # see PAHOLE_HAS_LANG_EXCLUDE
> +       extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
> +fi
>
>  echo ${extra_paholeopt}
> --
> 2.39.0
>