linux-kernel - Re: [PATCH] vmlinux.lds.h: Force-align ELF notes section to four bytes

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Message-Id: <20230427051410.2054787-1-joanbrugueram@gmail.com>
Date:   Thu, 27 Apr 2023 05:14:10 +0000
From:   Joan Bruguera Micó <joanbrugueram@...il.com>
To:     jpoimboe@...nel.org
Cc:     i.pear@...look.com, acme@...nel.org, alan.maguire@...cle.com,
        alexandref75@...il.com, bpf@...r.kernel.org, dxu@...uu.xyz,
        jforbes@...hat.com, linux-kernel@...r.kernel.org,
        olsajiri@...il.com, peterz@...radead.org, ptalbert@...hat.com,
        yhs@...com
Subject: Re: [PATCH] vmlinux.lds.h: Force-align ELF notes section to four bytes

PS: As additional information for posterity, there are various conditions that
explain why this is/was only a problem on some specific distributions:

* In addition to dwarves/pahole 1.24, binutils 2.40 seems to also be required
  for the problem to occur (in Arch, downgrading to binutils 2.39 fixes it).
* Debian (and thus derived distributions) configures binutils with
  `--disable-x86-used-note`, which by default disables emitting the GNU notes
  which ultimately cause the .notes section to be aligned to 8 bytes.

  On Debian Bookworm & Ubuntu 23.04, the problem reproduces when building like:
  ```
  export KCFLAGS="-Xassembler -mx86-used-note=yes"
  export KAFLAGS="-Xassembler -mx86-used-note=yes"
  make
  ```

Finally, here's a smaller .config to reproduce the problem on affected systems:
https://zealcharm.com/20230416-btf-dedup-bug-sample-configs/minimal-repro