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: <20240911210848.GA2659844@thelio-3990X>
Date: Wed, 11 Sep 2024 14:08:48 -0700
From: Nathan Chancellor <nathan@...nel.org>
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,
	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 08:03:57PM +0900, Masahiro Yamada 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>

Reviewed-by: Nathan Chancellor <nathan@...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
>