linux-kernel - Re: [PATCH bpf-next v4 5/8] kbuild: Sync kconfig when PAHOLE

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <8be2cafa00b759220e73a6ce837ac9a3ff52da1f.camel@gmail.com>
Date: Thu, 18 Dec 2025 11:21:04 -0800
From: Eduard Zingerman <eddyz87@...il.com>
To: Ihor Solodrai <ihor.solodrai@...ux.dev>, Alan Maguire	
 <alan.maguire@...cle.com>, Alexei Starovoitov <ast@...nel.org>, Andrea
 Righi	 <arighi@...dia.com>, Andrew Morton <akpm@...ux-foundation.org>,
 Andrii Nakryiko	 <andrii@...nel.org>, Bill Wendling <morbo@...gle.com>,
 Changwoo Min	 <changwoo@...lia.com>, Daniel Borkmann
 <daniel@...earbox.net>, David Vernet	 <void@...ifault.com>, Donglin Peng
 <dolinux.peng@...il.com>, Hao Luo	 <haoluo@...gle.com>, Jiri Olsa
 <jolsa@...nel.org>, John Fastabend	 <john.fastabend@...il.com>, Jonathan
 Corbet <corbet@....net>, Justin Stitt	 <justinstitt@...gle.com>, KP Singh
 <kpsingh@...nel.org>, Martin KaFai Lau	 <martin.lau@...ux.dev>, Nathan
 Chancellor <nathan@...nel.org>, Nick Desaulniers	
 <nick.desaulniers+lkml@...il.com>, Nicolas Schier <nsc@...nel.org>, Shuah
 Khan	 <shuah@...nel.org>, Song Liu <song@...nel.org>, Stanislav Fomichev	
 <sdf@...ichev.me>, Tejun Heo <tj@...nel.org>, Yonghong Song	
 <yonghong.song@...ux.dev>
Cc: bpf@...r.kernel.org, dwarves@...r.kernel.org,
 linux-kbuild@...r.kernel.org, 	linux-kernel@...r.kernel.org,
 sched-ext@...ts.linux.dev
Subject: Re: [PATCH bpf-next v4 5/8] kbuild: Sync kconfig when
 PAHOLE_VERSION changes

On Wed, 2025-12-17 at 16:33 -0800, Ihor Solodrai wrote:
> This patch implements kconfig re-sync when the pahole version changes
> between builds, similar to how it happens for compiler version change
> via CC_VERSION_TEXT.
> 
> Define PAHOLE_VERSION in the top-level Makefile and export it for
> config builds. Set CONFIG_PAHOLE_VERSION default to the exported
> variable.
> 
> Kconfig records the PAHOLE_VERSION value in
> include/config/auto.conf.cmd [1].
> 
> The Makefile includes auto.conf.cmd, so if PAHOLE_VERSION changes
> between builds, make detects a dependency change and triggers
> syncconfig to update the kconfig [2].
> 
> For external module builds, add a warning message in the prepare
> target, similar to the existing compiler version mismatch warning.
> 
> Note that if pahole is not installed or available, PAHOLE_VERSION is
> set to 0 by pahole-version.sh, so the (un)installation of pahole is
> treated as a version change.
> 
> See previous discussions for context [3].
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/kconfig/preprocess.c?h=v6.18#n91
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Makefile?h=v6.18#n815
> [3] https://lore.kernel.org/bpf/8f946abf-dd88-4fac-8bb4-84fcd8d81cf0@oracle.com/
> 
> Signed-off-by: Ihor Solodrai <ihor.solodrai@...ux.dev>
> ---

When building BPF selftest modules the pahole version change was
detected, but it seems that BTF rebuild was not triggered:

  $ (cd ./tools/testing/selftests/bpf/test_kmods/; make -j)
  make[1]: Entering directory '/home/ezingerman/bpf-next'
  make[2]: Entering directory '/home/ezingerman/bpf-next/tools/testing/selftests/bpf/test_kmods'
    CC [M]  bpf_testmod.o
    CC [M]  bpf_test_no_cfi.o
    CC [M]  bpf_test_modorder_x.o
    CC [M]  bpf_test_modorder_y.o
    CC [M]  bpf_test_rqspinlock.o
    MODPOST Module.symvers
    CC [M]  bpf_testmod.mod.o
    CC [M]  .module-common.o
    CC [M]  bpf_test_no_cfi.mod.o
    CC [M]  bpf_test_modorder_x.mod.o
    CC [M]  bpf_test_modorder_y.mod.o
    CC [M]  bpf_test_rqspinlock.mod.o
    LD [M]  bpf_test_modorder_x.ko
    LD [M]  bpf_testmod.ko
    LD [M]  bpf_test_modorder_y.ko
    LD [M]  bpf_test_no_cfi.ko
    BTF [M] bpf_test_modorder_x.ko
    LD [M]  bpf_test_rqspinlock.ko
    BTF     bpf_test_modorder_x.ko
    BTF [M] bpf_test_no_cfi.ko
    BTF [M] bpf_test_modorder_y.ko
    BTF [M] bpf_testmod.ko
    BTF     bpf_test_no_cfi.ko
    BTF     bpf_test_modorder_y.ko
    BTF [M] bpf_test_rqspinlock.ko
    BTF     bpf_testmod.ko
    BTF     bpf_test_rqspinlock.ko
    BTFIDS  bpf_test_modorder_x.ko
    BTFIDS  bpf_test_modorder_y.ko
    BTFIDS  bpf_test_no_cfi.ko
    BTFIDS  bpf_testmod.ko
    OBJCOPY bpf_test_modorder_x.ko.BTF
    BTFIDS  bpf_test_rqspinlock.ko
    OBJCOPY bpf_test_no_cfi.ko.BTF
    OBJCOPY bpf_test_modorder_y.ko.BTF
    OBJCOPY bpf_testmod.ko.BTF
    OBJCOPY bpf_test_rqspinlock.ko.BTF
  make[2]: Leaving directory '/home/ezingerman/bpf-next/tools/testing/selftests/bpf/test_kmods'
  make[1]: Leaving directory '/home/ezingerman/bpf-next'
  [~/bpf-next]
  $ (cd ./tools/testing/selftests/bpf/test_kmods/; make -j)
  make[1]: Entering directory '/home/ezingerman/bpf-next'
  make[2]: Entering directory '/home/ezingerman/bpf-next/tools/testing/selftests/bpf/test_kmods'
  make[2]: Leaving directory '/home/ezingerman/bpf-next/tools/testing/selftests/bpf/test_kmods'
  make[1]: Leaving directory '/home/ezingerman/bpf-next'

... update pahole from version 131 to 132 ...

  [~/bpf-next]
  $ (cd ./tools/testing/selftests/bpf/test_kmods/; make -j)
  make[1]: Entering directory '/home/ezingerman/bpf-next'
  make[2]: Entering directory '/home/ezingerman/bpf-next/tools/testing/selftests/bpf/test_kmods'
  warning: pahole version differs from the one used to build the kernel
    The kernel was built with: 131
    You are using:             132
  make[2]: Leaving directory '/home/ezingerman/bpf-next/tools/testing/selftests/bpf/test_kmods'
  make[1]: Leaving directory '/home/ezingerman/bpf-next'

Is this an expected behavior?