On Tue, Apr 8, 2025 at 8:08 AM Sami Tolvanen <samitolva...@google.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 after
> commit 47dcb534e253 ("btf_encoder: Stop indexing symbols for
> VARs") and 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
>
> As the issue occurs in pahole v1.28 and the fix was merged
> after v1.29 was released, require pahole <v1.28 or >v1.29 when
> GENDWARFKSYMS is enabled with DEBUG_INFO_BTF on X86.
>
> Reported-by: Paolo Pisati <paolo.pis...@canonical.com>
> Signed-off-by: Sami Tolvanen <samitolva...@google.com>
> ---
>
Applied to linux-kbuild.
Thanks.
> Changes in v2:
> - Also allow pahole <v1.28.
> - Update comment to include the affected commit range.
>
> ---
> kernel/module/Kconfig | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
> index d7762ef5949a..39278737bb68 100644
> --- a/kernel/module/Kconfig
> +++ b/kernel/module/Kconfig
> @@ -192,6 +192,11 @@ config GENDWARFKSYMS
> depends on !DEBUG_INFO_REDUCED && !DEBUG_INFO_SPLIT
> # Requires ELF object files.
> depends on !LTO
> + # To avoid conflicts with the discarded __gendwarfksyms_ptr symbols on
> + # X86, requires pahole before commit 47dcb534e253 ("btf_encoder: Stop
> + # indexing symbols for VARs") or after commit 9810758003ce
> ("btf_encoder:
> + # Verify 0 address DWARF variables are in ELF section").
> + depends on !X86 || !DEBUG_INFO_BTF || PAHOLE_VERSION < 128 ||
> PAHOLE_VERSION > 129
> help
> Calculate symbol versions from DWARF debugging information using
> gendwarfksyms. Requires DEBUG_INFO to be enabled.
>
> base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8
> --
> 2.49.0.504.g3bcea36a83-goog
>
--
Best Regards
Masahiro Yamada
