linux-kernel - Segfault in pahole 1.18 when building kernel 5.9.1 for arm64

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Message-ID: <CAFDeuWM7D-Upi84-JovKa3g8Y_4fjv65jND3--e9u-tER3WmVA@mail.gmail.com>
Date:   Sun, 18 Oct 2020 20:18:33 -0300
From:   Érico Rolim <erico.erc@...il.com>
To:     dwarves@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Segfault in pahole 1.18 when building kernel 5.9.1 for arm64

Hi!

I'm trying to build kernel 5.9.1 for arm64, and my dotconfig has
`CONFIG_DEBUG_INFO_BTF=y`, which requires pahole for building. However, pahole
version 1.18 segfaults during the build, as can be seen below:

PAHOLE: Error: Found symbol of zero size when encoding btf (sym:
'__kvm_nvhe_arm64_ssbd_callback_required', cu:
'arch/arm64/kernel/cpu_errata.c').
PAHOLE: Error: Use '-j' or '--force' to ignore such symbols and force
emit the btf.
scripts/link-vmlinux.sh: line 141: 43837 Segmentation fault
LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1}
  LD      .tmp_vmlinux.kallsyms1
  KSYM    .tmp_vmlinux.kallsyms1.o
  LD      .tmp_vmlinux.kallsyms2
  KSYM    .tmp_vmlinux.kallsyms2.o
  LD      vmlinux
  BTFIDS  vmlinux
FAILED: load BTF from vmlinux: Unknown error -2make: ***
[Makefile:1162: vmlinux] Error 255

It is possible to force the build to continue if

  LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1}

in scripts/link-vmlinux.sh is changed to

  LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J --btf_encode_force ${1}

The suggested `-j` or `--force` flags don't exist, since they were removed in
[1]. I believe `--btf_encode_force` should be suggested instead.

It should be noted that the same build, but with pahole version 1.17, works
without issue, so I think this is either a regression in pahole or the script
will need to be changed for newer versions of pahole.

- [1] https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/pahole.c?h=v1.18&id=1abc001417b579b86a9b27ff88c9095d8f498a46

Thanks,
Érico