linux-kernel - Re: [PATCH 2/3] btf: move pahole check in scripts/link-vmlinux.sh to lib/Kconfig.debug

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Message-ID: <CAEf4BzaMAj06RSAyVeaK-fWMEFJjEf6XDXZGzkk7K3k+n1q-nQ@mail.gmail.com>
Date: Wed, 11 Sep 2024 14:07:33 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: Martin KaFai Lau <martin.lau@...ux.dev>, bpf@...r.kernel.org, linux-arch@...r.kernel.org, 
	Andrii Nakryiko <andrii@...nel.org>, linux-kernel@...r.kernel.org, 
	Nathan Chancellor <nathan@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	Nicolas Schier <nicolas@...sle.eu>, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH 2/3] btf: move pahole check in scripts/link-vmlinux.sh to lib/Kconfig.debug

On Wed, Sep 11, 2024 at 4:04 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> When DEBUG_INFO_DWARF5 is selected, pahole 1.21+ is required to enable
> DEBUG_INFO_BTF.
>
> When DEBUG_INFO_DWARF4 or DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT is selected,
> DEBUG_INFO_BTF can be enabled without pahole installed, but a build error
> will occur in scripts/link-vmlinux.sh:
>
>     LD      .tmp_vmlinux1
>   BTF: .tmp_vmlinux1: pahole (pahole) is not available
>   Failed to generate BTF for vmlinux
>   Try to disable CONFIG_DEBUG_INFO_BTF
>
> We did not guard DEBUG_INFO_BTF by PAHOLE_VERSION when previously
> discussed [1].
>
> However, commit 613fe1692377 ("kbuild: Add CONFIG_PAHOLE_VERSION")
> added CONFIG_PAHOLE_VERSION at all. Now several CONFIG options, as
> well as the combination of DEBUG_INFO_BTF and DEBUG_INFO_DWARF5, are
> guarded by PAHOLE_VERSION.
>
> The remaining compile-time check in scripts/link-vmlinux.sh now appears
> to be an awkward inconsistency.
>
> This commit adopts Nathan's original work.
>
> [1]: https://lore.kernel.org/lkml/20210111180609.713998-1-natechancellor@gmail.com/
>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
>

LGTM

Acked-by: Andrii Nakryiko <andrii@...nel.org>

>  lib/Kconfig.debug       |  3 ++-
>  scripts/link-vmlinux.sh | 12 ------------
>  2 files changed, 2 insertions(+), 13 deletions(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 5e2f30921cb2..eff408a88dfd 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -379,12 +379,13 @@ config DEBUG_INFO_BTF
>         depends on !DEBUG_INFO_SPLIT && !DEBUG_INFO_REDUCED
>         depends on !GCC_PLUGIN_RANDSTRUCT || COMPILE_TEST
>         depends on BPF_SYSCALL
> +       depends on PAHOLE_VERSION >= 116
>         depends on !DEBUG_INFO_DWARF5 || PAHOLE_VERSION >= 121
>         # pahole uses elfutils, which does not have support for Hexagon relocations
>         depends on !HEXAGON
>         help
>           Generate deduplicated BTF type information from DWARF debug info.
> -         Turning this on expects presence of pahole tool, which will convert
> +         Turning this on requires presence of pahole tool, which will convert
>           DWARF type info into equivalent deduplicated BTF type info.
>
>  config PAHOLE_HAS_SPLIT_BTF
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index cfffc41e20ed..53bd4b727e21 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -111,20 +111,8 @@ vmlinux_link()
>  # ${1} - vmlinux image
>  gen_btf()
>  {
> -       local pahole_ver
>         local btf_data=${1}.btf.o
>
> -       if ! [ -x "$(command -v ${PAHOLE})" ]; then
> -               echo >&2 "BTF: ${1}: pahole (${PAHOLE}) is not available"
> -               return 1
> -       fi
> -
> -       pahole_ver=$(${PAHOLE} --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/')
> -       if [ "${pahole_ver}" -lt "116" ]; then
> -               echo >&2 "BTF: ${1}: pahole version $(${PAHOLE} --version) is too old, need at least v1.16"
> -               return 1
> -       fi
> -
>         info BTF "${btf_data}"
>         LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${PAHOLE_FLAGS} ${1}
>
> --
> 2.43.0
>