Re: [PATCH bpf-next v3 4/6] lib/Kconfig.debug: Set the minimum required pahole version to v1.22

[Alan Maguire <alan.maguire@oracle.com>]

On 05/12/2025 22:30, Ihor Solodrai wrote:
> Subsequent patches in the series change vmlinux linking scripts to
> unconditionally pass --btf_encode_detached to pahole, which was
> introduced in v1.22 [1][2].
> 
> This change allows to remove PAHOLE_HAS_SPLIT_BTF Kconfig option and
> other checks of older pahole versions.
> 
> [1] https://github.com/acmel/dwarves/releases/tag/v1.22
> [2] https://lore.kernel.org/bpf/cbafbf4e-9073-4383-8ee6-1353f9e5869c@oracle.com/
> 
> Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
> ---
>  lib/Kconfig.debug         | 13 ++++---------
>  scripts/Makefile.btf      |  9 +--------
>  tools/sched_ext/README.md |  1 -
>  3 files changed, 5 insertions(+), 18 deletions(-)
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 742b23ef0d8b..3abf3ae554b6 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -389,18 +389,13 @@ 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_DWARF4 || PAHOLE_VERSION >= 121
> +	depends on PAHOLE_VERSION >= 122
>  	# 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 requires pahole v1.16 or later (v1.21 or later to
> -	  support DWARF 5), which will convert DWARF type info into equivalent
> -	  deduplicated BTF type info.
> -
> -config PAHOLE_HAS_SPLIT_BTF
> -	def_bool PAHOLE_VERSION >= 119
> +	  Turning this on requires pahole v1.22 or later, which will convert
> +	  DWARF type info into equivalent deduplicated BTF type info.
>  
>  config PAHOLE_HAS_BTF_TAG
>  	def_bool PAHOLE_VERSION >= 123
> @@ -422,7 +417,7 @@ config PAHOLE_HAS_LANG_EXCLUDE
>  config DEBUG_INFO_BTF_MODULES
>  	bool "Generate BTF type information for kernel modules"
>  	default y
> -	depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF
> +	depends on DEBUG_INFO_BTF && MODULES
>  	help
>  	  Generate compact split BTF type information for kernel modules.
>  
> diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf
> index db76335dd917..7c1cd6c2ff75 100644
> --- a/scripts/Makefile.btf
> +++ b/scripts/Makefile.btf
> @@ -7,14 +7,7 @@ JOBS := $(patsubst -j%,%,$(filter -j%,$(MAKEFLAGS)))
>

hi Ihor, a small suggestion here, and it is orthogonal to what you're 
doing here, so just for consideration if you're planning a v4 since you're 
touching this file.

We've had problems in the past because we get pahole version from .config
in Makefile.btf

pahole-ver := $(CONFIG_PAHOLE_VERSION)

and it can be outdated.

Specifically the problem is that if "make oldconfig" is not run after
updating pahole we don't get the actual pahole version during builds
and options can be missing. See [1] for an example, but perhaps we
should do

pahole-ver := $(shell $(srctree)/scripts/pahole-version.sh)

in Makefile.btf to ensure the value reflects latest pahole and that
then determines which options we use? Andrii suggested an approach like
CC_VERSION_TEXT might be worth pursuing; AFAICT that recomputes the
CC_VERSION and warns the user if there is a version difference. Given that
the CONFIG pahole version requirements are all pretty modest - it might
simply be enough to recompute it in Makefile.btf and perhaps ensure it's 
not less than CONFIG_PAHOLE_VERSION. Just a thought anyway. Thanks!

Alan
 
[1] https://lore.kernel.org/bpf/CAEf4BzYi1xX3p_bY3j9dEuPvtCW3H7z=p2vdn-2GY0OOenxQAg@mail.gmail.com/