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

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Message-ID: <20250320232757.2283956-2-samitolvanen@google.com>
Date: Thu, 20 Mar 2025 23:27:58 +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, 
	Sami Tolvanen <samitolvanen@...gle.com>, Paolo Pisati <paolo.pisati@...onical.com>
Subject: [PATCH] kbuild: Require pahole >v1.29 with GENDWARFKSYMS and BTF on X86

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>
---
 kernel/module/Kconfig | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
index d7762ef5949a..7c75832aa1af 100644
--- a/kernel/module/Kconfig
+++ b/kernel/module/Kconfig
@@ -192,6 +192,10 @@ config GENDWARFKSYMS
 	depends on !DEBUG_INFO_REDUCED && !DEBUG_INFO_SPLIT
 	# Requires ELF object files.
 	depends on !LTO
+	# Requires pahole commit 9810758003ce ("btf_encoder: Verify 0 address
+	# DWARF variables are in ELF section") on X86 to avoid conflicts with
+	# __gendwarfksyms_ptr symbols.
+	depends on !X86 || !DEBUG_INFO_BTF || PAHOLE_VERSION > 129
 	help
 	  Calculate symbol versions from DWARF debugging information using
 	  gendwarfksyms. Requires DEBUG_INFO to be enabled.

base-commit: 4701f33a10702d5fc577c32434eb62adde0a1ae1
-- 
2.49.0.395.g12beb8f557-goog