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Message-ID: <85b89c11-8a97-49ec-9c5c-9b028d339195@linux.dev> Date: Mon, 15 Dec 2025 18:40:51 -0800 From: Ihor Solodrai <ihor.solodrai@...ux.dev> To: Alan Maguire <alan.maguire@...cle.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nsc@...nel.org>, Tejun Heo <tj@...nel.org>, David Vernet <void@...ifault.com>, Andrea Righi <arighi@...dia.com>, Changwoo Min <changwoo@...lia.com>, Shuah Khan <shuah@...nel.org>, Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, Donglin Peng <dolinux.peng@...il.com> Cc: bpf@...r.kernel.org, dwarves@...r.kernel.org, linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org Subject: Re: [PATCH bpf-next v3 4/6] lib/Kconfig.debug: Set the minimum required pahole version to v1.22 On 12/12/25 9:26 AM, Alan Maguire wrote: > 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@...ux.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. Hi Alan. v4 for sure, and maybe even v5, we'll see. > > 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! Yeah, I am aware of the issue. I am not sure version refresh in Makefile.btf would be enough, since there are config dependencies in Kconfig.debug. So we either need to trigger re-config, and maybe even force full kernel re-build, or somehow get rid of the version checks in the kconfig, which may be a challenge. I think the simplest thing we could is to check if the version has changed and fail the build. That's a "panic!" approach though. I'll look into how compiler versions are checked, maybe it's not that hard to add similar behavior for pahole. > > Alan > > [1] https://lore.kernel.org/bpf/CAEf4BzYi1xX3p_bY3j9dEuPvtCW3H7z=p2vdn-2GY0OOenxQAg@mail.gmail.com/ >
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