linux-kernel - Re: [PATCH] kbuild: Require pahole >v1.29 with GENDWARFKSYMS and BTF on X86

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Message-ID: <CABCJKudb3GVL-nfUvd=1rhyH_ZWnxQCQkZBdGXQ16pA5fg3yng@mail.gmail.com>
Date: Mon, 7 Apr 2025 23:05:59 +0000
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: Luis Chamberlain <mcgrof@...nel.org>, Petr Pavlu <petr.pavlu@...e.com>, 
	Daniel Gomez <da.gomez@...sung.com>, linux-modules@...r.kernel.org, 
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Paolo Pisati <paolo.pisati@...onical.com>
Subject: Re: [PATCH] kbuild: Require pahole >v1.29 with GENDWARFKSYMS and BTF
 on X86

Hi Masahiro,

On Sun, Apr 6, 2025 at 1:21 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> On Fri, Mar 21, 2025 at 8:28 AM Sami Tolvanen <samitolvanen@...gle.com> wrote:
> >
> > With CONFIG_GENDWARFKSYMS, __gendwarfksyms_ptr variables are added
> > to the kernel in EXPORT_SYMBOL() to ensure DWARF type information
> > is available for exported symbols in the TUs where they're actually
> > exported. These symbols are dropped when linking vmlinux, but
> > dangling references to them remain in DWARF.
> >
> > With CONFIG_DEBUG_INFO_BTF enabled on X86, pahole versions
> > before commit 9810758003ce ("btf_encoder: Verify 0 address
> > DWARF variables are in ELF section") place these symbols in the
> > .data..percpu section, which results in an "Invalid offset" error in
> > btf_datasec_check_meta() during boot, as all the variables are at
> > zero offset and have non-zero size. If CONFIG_DEBUG_INFO_BTF_MODULES
> > is enabled, this also results in a failure to load modules with:
> >
> >   failed to validate module [$module] BTF: -22
> >
> > The pahole commit that adds 0 address DWARF variable verification
> > was merged after v1.29 was released, so later versions of pahole
> > shouldn't have this issue. Require pahole >v1.29 when GENDWARFKSYMS
> > is enabled with DEBUG_INFO_BTF on X86.
> >
> > Reported-by: Paolo Pisati <paolo.pisati@...onical.com>
> > Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
>
> The issue occurs with
> 47dcb534e253 ("btf_encoder: Stop indexing symbols for VARs"),
> then fixed by  9810758003ce ("btf_encoder: Verify 0 address
> DWARF variables are in ELF section")
>
>
> Perhaps, does it make sense to do this?
>
>  depends on !X86 || !DEBUG_INFO_BTF || (PAHOLE_VERSION > 129 ||
> PAHOLE_VERSION < 128)

That's a good point. I confirmed that v1.27 works fine too. I'll send v2.

Sami